4-Channel, Low Noise, Low Power, 24-Bit, AD7124-4 Data Sheet

4-Channel, Low Noise, Low Power, 24-Bit, AD7124-4 Data Sheet
4-Channel, Low Noise, Low Power, 24-Bit,
Sigma-Delta ADC with PGA and Reference
AD7124-4
Data Sheet
FEATURES
Low-side power switch
General-purpose outputs
Multiple filter options
Internal temperature sensor
Self and system calibration
Sensor burnout detection
Automatic channel sequencer
Per channel configuration
Power supply: 2.7 V to 3.6 V and ±1.8 V
Independent interface power supply
Power-down current: 5 µA maximum
Temperature range: −40°C to +105°C
32-lead LFCSP/24-lead TSSOP
3-wire or 4-wire serial interface
SPI, QSPI, MICROWIRE, and DSP compatible
Schmitt trigger on SCLK
ESD: 4 kV
3 power modes
RMS noise
Low power: 24 nV rms at 1.17 SPS, gain = 128 (255 µA typical)
Mid power: 20 nV rms at 2.34 SPS, gain = 128 (355 µA typical)
Full power: 23 nV rms at 9.4 SPS, gain = 128 (930 µA typical)
Up to 22 noise free bits in all power modes (gain = 1)
Output data rate
Full power: 9.38 SPS to 19,200 SPS
Mid power: 2.34 SPS to 4800 SPS
Low power: 1.17 SPS to 2400 SPS
Rail-to-rail analog inputs for gains > 1
Simultaneous 50 Hz/60 Hz rejection at 25 SPS (single cycle
settling)
Diagnostic functions (which aid safe integrity level (SIL)
certification)
Crosspoint multiplexed analog inputs
4 differential/7 pseudo differential inputs
Programmable gain (1 to 128)
Band gap reference with 15 ppm/°C drift maximum (65 µA)
Matched programmable excitation currents
Internal clock oscillator
On-chip bias voltage generator
APPLICATIONS
Temperature measurement
Pressure measurement
Industrial process control
Instrumentation
Smart transmitters
FUNCTIONAL BLOCK DIAGRAM
1.9V
LDO
REGCAPA
REFOUT
VBIAS
CROSSPOINT
MUX
BANDGAP
REF
AVDD
AVSS
AIN2/IOUT/VBIAS/P1
BURNOUT
DETECT
AIN4/IOUT/VBIAS
AIN5/IOUT/VBIAS
24-BIT
Σ-Δ ADC
PGA2
BUF
ANALOG
BUFFERS
AVSS
AIN7/IOUT/VBIAS/REFIN2(–)
VARIABLE
DIGITAL
FILTER
DIAGNOSTICS
POWER
SWITCH
AVDD
SERIAL
INTERFACE
AND
CONTROL
LOGIC
CHANNEL
SEQUENCER
GPOs
TEMPERATURE
SENSOR
PSW
BUF
PGA1
X-MUX
AIN6/IOUT/VBIAS/REFIN2(+)
1.8V
LDO
REFERENCE
BUFFERS
AIN1/IOUT/VBIAS
AIN3/IOUT/VBIAS/P2
REFIN2(+)
REFIN2(–)
AVSS
AVDD
AIN0/IOUT/VBIAS
IOVDD REGCAPD
REFIN1(+) REFIN1(–)
DOUT/RDY
DIN
SCLK
CS
SYNC
DIAGNOSTICS
COMMUNICATIONS
POWER SUPPLY
SIGNAL CHAIN
DIGITAL
EXCITATION
CURRENTS
INTERNAL
CLOCK
AD7124-4
AVSS
AVSS
DGND
CLK
13197-001
AVDD
Figure 1.
Rev. A
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AD7124-4
Data Sheet
TABLE OF CONTENTS
Features .............................................................................................. 1 Span and Offset Limits .............................................................. 52 Applications ....................................................................................... 1 System Synchronization ............................................................ 52 Functional Block Diagram .............................................................. 1 Digital Filter .................................................................................... 53 Revision History ............................................................................... 3 Sinc4 Filter ................................................................................... 53 General Description ......................................................................... 4 Sinc3 Filter ................................................................................... 55 Specifications..................................................................................... 5 Fast Settling Mode (Sinc4 + Sinc1 Filter) .................................. 57 Timing Characteristics .............................................................. 10 Fast Settling Mode (Sinc3 + Sinc1 Filter) .................................. 59 Absolute Maximum Ratings.......................................................... 13 Post Filters ................................................................................... 61 Thermal Resistance .................................................................... 13 Summary of Filter Options ....................................................... 64 ESD Caution ................................................................................ 13 Diagnostics ...................................................................................... 65 Pin Configuration and Function Descriptions ........................... 14 Signal Chain Check .................................................................... 65 Typical Performance Characteristics ........................................... 17 Reference Detect ......................................................................... 65 Terminology .................................................................................... 26 Calibration, Conversion, and Saturation Errors .................... 65 RMS Noise and Resolution............................................................ 27 Overvoltage/Undervoltage Detection ..................................... 65 Full Power Mode......................................................................... 27 Power Supply Monitors ............................................................. 66 Mid Power Mode ........................................................................ 30 LDO Monitoring ........................................................................ 66 Low Power Mode ........................................................................ 33 MCLK Counter ........................................................................... 66 Getting Started ................................................................................ 36 SPI SCLK Counter...................................................................... 66 Overview...................................................................................... 36 SPI Read/Write Errors ............................................................... 67 Power Supplies ............................................................................ 37 SPI_IGNORE Error ................................................................... 67 Digital Communication............................................................. 37 Checksum Protection ................................................................ 67 Configuration Overview ........................................................... 39 Memory Map Checksum Protection ....................................... 67 ADC Circuit Information .............................................................. 44 Burnout Currents ....................................................................... 69 Analog Input Channel ............................................................... 44 Temperature Sensor ................................................................... 69 Programmable Gain Array (PGA) ........................................... 45 Grounding and Layout .................................................................. 70 Reference ..................................................................................... 45 Applications Information .............................................................. 71 Bipolar/Unipolar Configuration .............................................. 45 Temperature Measurement Using a Thermocouple .............. 71 Data Output Coding .................................................................. 46 Temperature Measurement Using an RTD ............................. 72 Excitation Currents .................................................................... 46 Flowmeter.................................................................................... 74 Bridge Power-Down Switch ...................................................... 47 On-Chip Registers .......................................................................... 76 Logic Outputs.............................................................................. 47 Communications Register ......................................................... 77 Bias Voltage Generator .............................................................. 47 Status Register ............................................................................. 77 Clock ............................................................................................ 47 ADC_CONTROL Register ....................................................... 78 Power Modes ............................................................................... 47 Data Register ............................................................................... 80 Standby and Power-Down Modes ............................................ 48 IO_CONTROL_1 Register........................................................ 80 Digital Interface .......................................................................... 48 IO_CONTROL_2 Register........................................................ 82 DATA_STATUS .......................................................................... 50 ID Register................................................................................... 82 Serial Interface Reset (DOUT_RDY_DEL and CS_EN Bits) 50 Error Register .............................................................................. 82 Reset ............................................................................................. 50 ERROR_EN Register ................................................................. 83 Calibration ................................................................................... 51 MCLK_COUNT Register.......................................................... 85 Rev. A | Page 2 of 90
Data Sheet
AD7124-4
Channel Registers........................................................................85
Gain Registers .............................................................................. 89
Configuration Registers .............................................................87
Outline Dimensions ........................................................................ 90
Filter Registers .............................................................................88
Ordering Guide ........................................................................... 90
Offset Registers ............................................................................89
REVISION HISTORY
7/15—Rev. 0 to Rev. A
Change to Data Sheet Title............................................................... 1
Changes to Internal Reference Drift Parameter, Table 2.............. 7
Changes to Figure 30 ......................................................................20
Change to Digital Outputs Section ...............................................37
Change to Single Conversion Mode Section ...............................49
Changes to Calibration Section .....................................................51
Changes to Figure 83 ......................................................................53
Changes to Figure 91 ......................................................................56
Changes to Figure 99 ......................................................................58
Changes to Figure 105 ....................................................................60
Changes to Reference Detect Section and Figure 119 ................65
Change to Table 70 ..........................................................................83
Changes to Table 71 ........................................................................84
5/15—Revision 0: Initial Version
Rev. A | Page 3 of 90
AD7124-4
Data Sheet
GENERAL DESCRIPTION
The AD7124-4 is a low power, low noise, completely integrated
analog front end for high precision measurement applications.
The device contains a low noise, 24-bit Σ-Δ analog-to-digital
converter (ADC), and can be configured to have four differential
inputs or seven single-ended or pseudo differential inputs. The
on-chip low gain stage ensures that signals of small amplitude
can be interfaced directly to the ADC.
One of the major advantages of the AD7124-4 is that it gives the
user the flexibility to employ one of three integrated power
modes. The current consumption, range of output data rates,
and rms noise can be tailored with the power mode selected.
The device also offers a multitude of filter options, ensuring that
the user has the highest degree of flexibility.
The AD7124-4 can achieve simultaneous 50 Hz and 60 Hz
rejection when operating at an output data rate of 25 SPS (single
cycle settling), with rejection in excess of 80 dB achieved at lower
output data rates.
The AD7124-4 establishes the highest degree of signal chain
integration. The device contains a precision, low noise, low
drift internal band gap reference, and also accepts an external
differential reference, which can be internally buffered. Other
key integrated features include programmable low drift excitation
current sources, burnout currents, and a bias voltage generator,
which sets the common-mode voltage of a channel to AVDD/2.
The low-side power switch enables the user to power down
bridge sensors between conversions, ensuring the absolute
minimal power consumption of the system. The device also
allows the user the option of operating with either an internal
clock or an external clock.
The integrated channel sequencer allows several channels to be
enabled simultaneously, and the AD7124-4 sequentially converts
on each enabled channel, simplifying communication with the
device. As many as 16 channels can be enabled at any time; a
channel being defined as an analog input or a diagnostic such
as a power supply check or a reference check. This unique
feature allows diagnostics to be interleaved with conversions.
The AD7124-4 also supports per channel configuration. The
device allows eight configurations or setups. Each configuration
consists of gain, filter type, output data rate, buffering, and
reference source. The user can assign any of these setups on a
channel by channel basis.
The AD7124-4 also has extensive diagnostic functionality
integrated as part of its comprehensive feature set. These
diagnostics include a cyclic redundancy check (CRC), signal
chain checks, and serial interface checks, which lead to a more
robust solution. These diagnostics reduce the need for external
components to implement diagnostics, resulting in reduced
board space needs, reduced design cycle times, and cost savings.
The failure modes effects and diagnostic analysis (FMEDA) of a
typical application has shown a safe failure fraction (SFF) greater
than 90% according to IEC 61508.
The device operates with a single analog power supply from 2.7 V
to 3.6 V or a dual 1.8 V power supply. The digital supply has a
range of 1.65 V to 3.6 V. It is specified for a temperature range
of −40°C to +105°C. The AD7124-4 is housed in a 32-lead
LFCSP package and a 24-lead TSSOP package.
Note that, throughout this data sheet, multifunction pins, such
as DOUT/RDY, are referred to either by the entire pin name or
by a single function of the pin, for example, RDY, when only
that function is relevant.
Table 1. AD7124-4 Overview
Parameter
Maximum Output Data Rate
RMS Noise (Gain = 128)
Peak-to-Peak Resolution at 1200 SPS
(Gain = 1)
Typical Current (ADC + PGA)
Low Power Mode
2400 SPS
24 nV
16.4 bits
Mid Power Mode
4800 SPS
20 nV
17.1 bits
Full Power Mode
19,200 SPS
23 nV
18 bits
255 µA
355 µA
930 µA
Rev. A | Page 4 of 90
Data Sheet
AD7124-4
SPECIFICATIONS
AVDD = 2.9 V to 3.6 V (full power mode), 2.7 V to 3.6 V (mid and low power mode), IOVDD = 1.65 V to 3.6 V, AVSS = DGND = 0 V,
REFINx(+) = 2.5 V, REFINx(−) = AVSS, all specifications TMIN to TMAX, unless otherwise noted.
Table 2.
Parameter1
ADC
Output Data Rate, fADC
Low Power Mode
Mid Power Mode
Full Power Mode
No Missing Codes2
Min
Typ
1.17
2.34
9.38
24
24
Max
Unit
2400
4800
19,200
SPS
SPS
SPS
Bits
Bits
Resolution
RMS Noise and Update Rates
Integral Nonlinearity (INL)
Low Power Mode2
Mid Power Mode2
Full Power Mode
−4
−15
−20
−4
−15
−4
−15
Offset Error4
Before Calibration
After Internal Calibration/System
Calibration
Offset Error Drift vs. Temperature5
Low Power Mode
Mid Power Mode
Full Power Mode
Gain Error4, 6
Before Internal Calibration
After Internal Calibration
−0.016
Mid Power Mode2
Full Power Mode
+4
+15
+20
+4
+15
+4
+15
FS3 > 2, sinc4 filter
FS3 > 8, sinc3 filter
See the RMS Noise and Resolution
section
See the RMS Noise and Resolution
section
ppm of FSR
ppm of FSR
ppm of FSR
ppm of FSR
ppm of FSR
ppm of FSR
ppm of FSR
Gain = 1
Gain > 1, TA = −40°C to +85°C
Gain > 1, TA = −40°C to +105°C
Gain = 1
Gain > 1
Gain = 12
Gain > 1
±15
200/gain
In order of
noise
µV
µV
Gain = 1 to 8
Gain = 16 to 128
10
80
40
10
40
20
10
nV/°C
nV/°C
nV/°C
nV/°C
nV/°C
nV/°C
nV/°C
Gain = 1 or gain > 16
Gain = 2 to 8
Gain = 16
Gain = 1 or gain > 16
Gain = 2 to 8
Gain = 16
%
%
%
%
Gain = 1, TA = 25°C
Gain > 1
Gain = 2 to 8, TA = 25°C
Gain = 16 to 128
−0.0025
After System Calibration
Gain Error Drift vs. Temperature
Power Supply Rejection
Low Power Mode
±1
±2
±2
±1
±2
±1
±2
Test Conditions/Comments
+0.0025
−0.3
+0.004
±0.025
In order of
noise
1
+0.016
2
84
91
89
95
96
ppm/°C
dB
dB
dB
dB
dB
Rev. A | Page 5 of 90
AIN = 1 V/gain, external reference
Gain = 2 to 16
Gain = 1 or gain > 16
Gain = 2 to 16
Gain = 1 or gain > 16
AD7124-4
Parameter1
Common-Mode Rejection7
At DC2
At DC
Sinc3, Sinc4 Filter2
At 50 Hz, 60 Hz
At 50 Hz
At 60 Hz
Fast Settling Filters2
At 50 Hz
At 60 Hz
Post Filters2
At 50 Hz, 60 Hz
Normal Mode Rejection2
Sinc4 Filter
External Clock
At 50 Hz, 60 Hz
At 50 Hz
At 60 Hz
Internal Clock
At 50 Hz, 60 Hz
At 50 Hz
At 60 Hz
Sinc3 Filter
External Clock
At 50 Hz, 60 Hz
At 50 Hz
At 60 Hz
Internal Clock
At 50 Hz, 60 Hz
At 50 Hz
At 60 Hz
Fast Settling Filters
External Clock
At 50 Hz
At 60 Hz
Internal Clock
At 50 Hz
At 60 Hz
Post Filters
External Clock
At 50 Hz, 60 Hz
Internal Clock
At 50 Hz, 60 Hz
Data Sheet
Min
Typ
85
100
110
90
105
115
Max
Unit
Test Conditions/Comments
dB
dB
dB
AIN = 1 V, gain = 1
AIN = 1 V/gain, gain 2 or 4
AIN = 1 V/gain, gain ≥ 8
120
120
120
dB
dB
dB
10 SPS, 50 Hz ± 1 Hz, 60 Hz ± 1 Hz
50 SPS, 50 Hz ± 1 Hz
60 SPS, 60 Hz ± 1 Hz
115
115
dB
dB
First notch at 50 Hz, 50 Hz ± 1 Hz
First notch at 60 Hz, 60 Hz ± 1 Hz
130
130
dB
dB
20 SPS, 50 Hz ± 1 Hz, 60 Hz ± 1 Hz
25 SPS, 50 Hz ± 1 Hz, 60 Hz ± 1 Hz
120
82
dB
dB
120
120
dB
dB
10 SPS, 50 Hz ± 1 Hz, 60 Hz ± 1 Hz
50 SPS, REJ608=1, 50 Hz ± 1 Hz,
60 Hz ± 1 Hz
50 SPS, 50 Hz ± 1 Hz
60 SPS, 60 Hz ± 1 Hz
98
66
dB
dB
92
92
dB
dB
100
66
dB
dB
100
100
dB
dB
73
52
dB
dB
68
68
dB
dB
10 SPS, 50 Hz ± 1 Hz, 60 Hz ± 1 Hz
50 SPS, REJ608 = 1, 50 Hz ± 1 Hz,
60 Hz ± 1 Hz
50 SPS, 50 Hz ± 1 Hz
60 SPS, 60 Hz ± 1 Hz
40
40
dB
dB
First notch at 50 Hz, 50 Hz ± 0.5 Hz
First notch at 60 Hz, 60 Hz ± 0.5 Hz
24.5
24.5
dB
dB
First notch at 50 Hz, 50 Hz ± 0.5 Hz
First notch at 60 Hz, 60 Hz ± 0.5 Hz
86
62
dB
dB
20 SPS, 50 Hz ± 1 Hz, 60 Hz ± 1 Hz
25 SPS, 50 Hz ± 1 Hz, 60 Hz ± 1 Hz
67
50
dB
dB
20 SPS, 50 Hz ± 1 Hz, 60 Hz ± 1 Hz
25 SPS, 50 Hz ± 1 Hz, 60 Hz ± 1 Hz
Rev. A | Page 6 of 90
10 SPS, 50 Hz ± 1 Hz, 60 Hz ± 1 Hz
50 SPS, REJ608 = 1, 50 Hz ± 1 Hz,
60 Hz ± 1 Hz
50 SPS, 50 Hz ± 1 Hz
60 SPS, 60 Hz ± 1 Hz
10 SPS, 50 Hz ± 1 Hz, 60 Hz ± 1 Hz
50 SPS, REJ608 = 1, 50 Hz ± 1 Hz,
60 Hz ± 1 Hz
50 SPS, 50 Hz ± 1 Hz
60 SPS, 60 Hz ± 1 Hz
Data Sheet
Parameter1
ANALOG INPUTS9
Differential Input Voltage Ranges10
Absolute AIN Voltage Limits2
Gain = 1 (Unbuffered)
Gain = 1 (Buffered)
Gain > 1
Analog Input Current
Gain > 1 or Gain = 1 (Buffered)
Low Power Mode
Absolute Input Current
Differential Input Current
Analog Input Current Drift
Mid Power Mode
Absolute Input Current
Differential Input Current
Analog Input Current Drift
Full Power Mode
Absolute Input Current
Differential Input Current
Analog Input Current Drift
Gain = 1 (Unbuffered)
Absolute Input Current
Analog Input Current Drift
REFERENCE INPUT
Internal Reference
Initial Accuracy
Drift
Output Current
Load Regulation
Power Supply Rejection
External Reference
External REFIN Voltage2
Absolute REFIN Voltage Limits2
Reference Input Current
Buffered
Low Power Mode
Absolute Input Current
Reference Input Current Drift
Mid Power Mode
Absolute Input Current
Reference Input Current Drift
Full Power Mode
Absolute Input Current
Reference Input Current Drift
Unbuffered
Absolute Input Current
Reference Input Current Drift
Normal Mode Rejection
Common-Mode Rejection
AD7124-4
Min
Typ
Max
±VREF/gain
AVSS − 0.05
AVSS + 0.1
AVSS − 0.05
AVDD + 0.05
AVDD − 0.1
AVDD + 0.05
Unit
Test Conditions/Comments
V
VREF = REFINx(+) − REFINx(−), or
internal reference
V
V
V
±1
±0.2
25
nA
nA
pA/°C
±1.2
±0.4
25
nA
nA
pA/°C
±3.3
±1.5
25
nA
nA
pA/°C
±2.65
1.1
µA/V
nA/V/°C
Current varies with input voltage
2.5 − 0.2%
2.5
2
2
2.5 + 0.2%
10
15
10
V
ppm/°C
ppm/°C
mA
µV/mA
dB
TA = 25°C
TSSOP
LFCSP
AVDD
AVDD + 0.05
AVDD − 0.1
V
V
V
REFIN = REFINx(+) − REFINx(−)
Unbuffered
Buffered
50
85
1
AVSS − 0.05
AVSS + 0.1
2.5
±0.5
10
nA
pA/°C
±1
10
nA
pA/°C
±3
10
nA
pA/°C
±12
6
µA
nA/°C
100
dB
Same as for analog inputs
Rev. A | Page 7 of 90
AD7124-4
Parameter1
EXCITATION CURRENT SOURCES (IOUT0/IOUT1)
Output Current
Data Sheet
Min
5
2
0.2
Hysteresis
Input Currents
Input Capacitance
%
ppm/°C
%
AVDD − 0.37
AVSS − 0.05
AVDD − 0.48
V
30
µs/nF
±0.5
13,584
°C
Codes/°C
10
30
0.5/2/4
AVDD − 0.6
0.4
1.6
1.55
1
0.7
AVDD + 0.04
AVSS − 0.04
614.4 − 5%
614.4
50:50
614.4 + 5%
2.4576
45:55 to 55:45
0.3 × IOVDD
0.35 × IOVDD
0.7
0.7 × IOVDD
0.65 × IOVDD
1.7
2
0.2
−1
TA = 25°C
Matching between IOUT0 and
IOUT1, VOUT = 0 V
AVDD = 3 V ± 5%
50 µA/100 µA/250 µA/500 µA
current sources, 2% accuracy
750 µA and 1000 µA current
sources, 2% accuracy
Available on any analog input pin
V
AVSS + (AVDD −
AVSS)/2
6.7
7
Test Conditions/Comments
Available on any analog input pin
µA
AVSS − 0.05
VBIAS Generator Start-Up Time
High, VINH
Unit
ppm/°C
%/V
%/V
V
BIAS VOLTAGE (VBIAS) GENERATOR
VBIAS
TEMPERATURE SENSOR
Accuracy
Sensitivity
LOW-SIDE POWER SWITCH
On Resistance (RON)
Allowable Current2
BURNOUT CURRENTS
AIN Current
DIGITAL OUTPUTS (P1 to P4)
Output Voltage
High, VOH
Low, VOL
DIAGNOSTICS
Power Supply Monitor Detect Level
Analog Low Dropout Regulator (ALDO)
Digital LDO (DLDO)
Reference Detect Level
AINM/AINP Overvoltage Detect Level
AINM/AINP Undervoltage Detect Level
INTERNAL/EXTERNAL CLOCK
Internal Clock
Frequency
Duty Cycle
External Clock
Frequency
Duty Cycle Range
LOGIC INPUTS2
Input Voltage
Low, VINL
Max
50/100/250/
500/750/1000
±4
50
±0.5
Initial Tolerance
Drift
Current Matching
Drift Matching
Line Regulation (AVDD)
Load Regulation
Output Compliance2
Typ
0.6
+1
10
Rev. A | Page 8 of 90
Dependent on the capacitance
connected to AIN
Ω
mA
Continuous current
µA
Analog inputs must be buffered
V
V
ISOURCE = 100 µA
ISINK = 100 µA
V
V
V
V
V
AVDD − AVSS ≥ 2.7 V
IOVDD ≥ 1.75 V
REF_DET_ERR bit active if VREF < 0.7 V
kHz
%
MHz
%
Internal divide by 4
V
V
V
V
V
V
V
V
µA
pF
1.65 V ≤ IOVDD < 1.9 V
1.9 V ≤ IOVDD < 2.3 V
2.3 V ≤ IOVDD ≤ 3.6 V
1.65 V ≤ IOVDD < 1.9 V
1.9 V ≤ IOVDD < 2.3 V
2.3 V ≤ IOVDD < 2.7 V
2.7 V ≤ IOVDD ≤ 3.6 V
1.65 V ≤ IOVDD ≤ 3.6 V
VIN = IOVDD or GND
All digital inputs
Data Sheet
Parameter1
LOGIC OUTPUTS (INCLUDING CLK)
Output Voltage2
High, VOH
Low, VOL
Floating State Leakage Current
Floating State Output Capacitance
Data Output Coding
SYSTEM CALIBRATION2
Calibration Limit
Full-Scale
Zero-Scale
Input Span
POWER SUPPLY VOLTAGES FOR ALL POWER
MODES
AVDD to AVSS
Low Power Mode
Mid Power Mode
Full Power Mode
IOVDD to GND
AVSS to GND
IOVDD to AVSS
POWER SUPPLY CURRENTS9, 11
IAVDD, External Reference
Low Power Mode
Gain = 12
Gain = 1 IAVDD Increase per AIN Buffer2
Gain = 2 to 8
Gain = 16 to 128
IAVDD Increase per Reference Buffer2
Mid Power Mode
Gain = 12
Gain = 1 IAVDD Increase per AIN Buffer2
Gain = 2 to 8
Gain = 16 to 128
IAVDD Increase per Reference Buffer2
Full Power Mode
Gain = 12
Gain = 1 IAVDD Increase per AIN Buffer2
Gain = 2 to 8
Gain = 16 to 128
IAVDD Increase per Reference Buffer2
IAVDD Increase
Due to Internal Reference2
Due to VBIAS2
Due to Diagnostics2
IIOVDD
Low Power Mode
Mid Power Mode
Full Power Mode
AD7124-4
Min
Typ
Max
Unit
Test Conditions/Comments
0.4
+1
V
V
µA
pF
ISOURCE = 100 µA
ISINK = 100 µA
IOVDD − 0.35
−1
10
Offset binary
1.05 × FS
2.1 × FS
V
V
V
3.6
3.6
3.6
3.6
+1.8
5.4
V
V
V
V
V
V
125
15
205
235
10
135
20
235
280
15
µA
µA
µA
µA
µA
150
30
275
330
20
165
35
325
405
30
µA
µA
µA
µA
µA
315
90
660
875
85
345
125
790
1100
110
µA
µA
µA
µA
µA
50
65
µA
15
4
20
5
µA
µA
20
25
55
35
40
85
µA
µA
µA
−1.05 × FS
0.8 × FS
2.7
2.7
2.9
1.65
−1.8
0
Rev. A | Page 9 of 90
All buffers off
All gains
All buffers off
All gains
All buffers off
All gains
Independent of power mode; the
reference buffers are not required
when using this reference
Independent of power mode
AD7124-4
Data Sheet
Parameter1
POWER-DOWN CURRENTS11
Standby Current
IAVDD
IIOVDD
Power-Down Current
IAVDD
IIOVDD
Min
Typ
Max
Unit
Test Conditions/Comments
Independent of power mode
7
8
12
17
µA
µA
LDOs on only
1
1
3
2
µA
µA
Temperature range = −40°C to +105°C.
These specifications are not production tested but are supported by characterization data at the initial product release.
FS is the decimal equivalent of the FS[10:0] bits in the filter registers.
4
Following a system or internal zero-scale calibration, the offset error is in the order of the noise for the programmed gain and output data rate selected. A system fullscale calibration reduces the gain error to the order of the noise for the programmed gain and output data rate.
5
Recalibration at any temperature removes these errors.
6
Gain error applies to both positive and negative full-scale. A factory calibration is performed at gain = 1, TA = 25°C.
7
When gain > 1, the common-mode voltage is between (AVSS + 0.1 + 0.1/gain) and (AVDD − 0.1 − 0.5/gain).
8
REJ60 is a bit in the filter registers. When the first notch of the sinc filter is at 50 Hz, a notch is placed at 60 Hz when REJ60 is set to 1. This gives simultaneous 50 Hz and
60 Hz rejection.
9
When the gain is greater than 1, the analog input buffers are enabled automatically. The buffers can only be disabled when the gain equals 1.
10
When VREF = (AVDD − AVSS), the typical differential input equals 0.92 × VREF/gain for the low and mid power modes and 0.86 × VREF/gain for full power mode.
11
The digital inputs are equal to IOVDD or DGND with excitation currents and bias voltage generator disabled.
1
2
3
TIMING CHARACTERISTICS
AVDD = 2.9 V to 3.6 V (full power mode), 2.7 V to 3.6 V (mid and low power mode), IOVDD = 1.65 V to 3.6 V, AVSS = DGND = 0 V, Input
Logic 0 = 0 V, Input Logic 1 = IOVDD, unless otherwise noted.
Table 3.
Parameter1, 2
t3
t4
t12
Min
100
100
Typ
Max
3/MCLK3
12/MCLK
24/MCLK
Unit
ns
ns
ns
ns
ns
µs
t13
6
25
50
µs
µs
µs
t14
3/MCLK
12/MCLK
24/MCLK
READ OPERATION
t1
t24
t56, 7
t6
t78
t
7
7A
0
0
10
0
ns
ns
ns
80
80
80
ns
ns
ns
ns
10
ns
110
t5
ns
ns
Rev. A | Page 10 of 90
Test Conditions/Comments
SCLK high pulse width
SCLK low pulse width
Delay between consecutive read/write operations
Full power mode
Mid power mode
Low power mode
DOUT/RDY high time if DOUT/RDY is low and the next
conversion is available
Full power mode
Mid power mode
Low power mode
SYNC low pulse width
Full power mode
Mid power mode
Low power mode
CS falling edge to DOUT/RDY active time
SCLK active edge5 to data valid delay
Bus relinquish time after CS inactive edge
SCLK inactive edge to CS inactive edge
SCLK inactive edge to DOUT/RDY high
The DOUT_RDY_DEL bit is cleared, the CS_EN bit is
cleared
The DOUT_RDY_DEL bit is set, the CS_EN bit is cleared
Data valid after CS inactive edge, the CS_EN bit is set
Data Sheet
Parameter1, 2
WRITE OPERATION
t8
t9
t10
t11
AD7124-4
Min
Typ
Max
0
30
25
0
Unit
Test Conditions/Comments
ns
ns
ns
ns
CS falling edge to SCLK active edge5 setup time
Data valid to SCLK edge setup time
Data valid to SCLK edge hold time
CS rising edge to SCLK edge hold time
These specifications were sample tested during the initial release to ensure compliance. All input signals are specified with tR = tF = 5 ns (10% to 90% of IOVDD and
timed from a voltage level of IOVDD/2.
2
See Figure 3, Figure 4, Figure 5, and Figure 6.
3
MCLK is the master clock frequency.
4
These specifications are measured with the load circuit shown in Figure 2 and defined as the time required for the output to cross the VOL or VOH limits.
5
The SCLK active edge is the falling edge of SCLK.
6
These specifications are derived from the measured time taken by the data output to change by 0.5 V when loaded with the circuit shown in Figure 2. The measured
number is then extrapolated back to remove the effects of charging or discharging the 25 pF capacitor. The times quoted in the timing characteristics are the true bus
relinquish times of the device and, therefore, are independent of external bus loading capacitances.
7 RDY
returns high after a read of the ADC. In single conversion mode and continuous conversion mode, the same data can be read again, if required, while RDY is high,
although subsequent reads must not occur close to the next output update. In continuous read mode, the digital word can be read only once.
8
When the CS_EN bit is cleared, the DOUT/RDY pin changes from its DOUT function to its RDY function, following the last inactive edge of the SCLK. When CS_EN is set,
the DOUT pin continues to output the LSB of the data until the CS inactive edge.
1
Timing Diagrams
ISINK (100µA)
TO OUTPUT PIN
IOVDD/2
25pF
13197-002
ISOURCE (100µA)
Figure 2. Load Circuit for Timing Characterization
CS (I)
t6
t1
DOUT/RDY (O)
MSB
t5
LSB
t2
t7
t3
I = INPUT, O = OUTPUT
t4
Figure 3. Read Cycle Timing Diagram (CS_EN Bit Cleared)
Rev. A | Page 11 of 90
13197-003
SCLK (I)
AD7124-4
Data Sheet
CS (I)
t6
t1
t5
DOUT/RDY (O)
MSB
LSB
t7A
t2
t3
13197-004
SCLK (I)
t4
I = INPUT, O = OUTPUT
Figure 4. Read Cycle Timing Diagram (CS_EN Bit Set)
CS (I)
t11
t8
SCLK (I)
t9
t10
MSB
LSB
13197-005
DIN (I)
I = INPUT, O = OUTPUT
Figure 5. Write Cycle Timing Diagram
t12
WRITE
DIN
WRITE
t12
t12
READ
READ
13197-006
DOUT/RDY
SCLK
Figure 6. Delay Between Consecutive Serial Operations
CS
DIN
t13
13197-007
DOUT/RDY
SCLK
Figure 7. DOUT/RDY High Time when DOUT/RDY is Initially Low and the Next Conversion is Available
SYNC (I)
13197-008
t14
MCLK (I)
Figure 8. SYNC Pulse Width
Rev. A | Page 12 of 90
Data Sheet
AD7124-4
ABSOLUTE MAXIMUM RATINGS
TA = 25°C, unless otherwise noted.
THERMAL RESISTANCE
Table 4.
θJA is specified for the worst case conditions, that is, a device
soldered in a circuit board for surface-mount packages.
Parameter
AVDD to AVSS
IOVDD to DGND
IOVDD to DGND
IOVDD to AVSS
AVSS to DGND
Analog Input Voltage to AVSS
Reference Input Voltage to AVSS
Digital Input Voltage to DGND
Digital Output Voltage to DGND
AINx/Digital Input Current
Operating Temperature Range
Storage Temperature Range
Maximum Junction Temperature
Lead Temperature, Soldering
Reflow
ESD Ratings
Human Body Model (HBM)
Field-Induced Charged Device
Model (FICDM)
Machine Model
Rating
−0.3 V to +3.96 V
−0.3 V to +3.96 V
−0.3 V to +3.96 V
−0.3 V to +5.94 V
−1.98 V to +0.3 V
−0.3 V to AVDD + 0.3 V
−0.3 V to AVDD + 0.3 V
−0.3 V to IOVDD + 0.3 V
−0.3 V to IOVDD + 0.3 V
10 mA
−40°C to +105°C
−65°C to +150°C
150°C
Table 5. Thermal Resistance
Package Type
32-Lead LFCSP
24-Lead TSSOP
ESD CAUTION
260°C
4 kV
1250 V
400 V
Stresses at or above those listed under Absolute Maximum
Ratings may cause permanent damage to the product. This is a
stress rating only; functional operation of the product at these
or any other conditions above those indicated in the operational
section of this specification is not implied. Operation beyond
the maximum operating conditions for extended periods may
affect product reliability.
Rev. A | Page 13 of 90
θJA
32.5
128
θJC
32.71
42
Unit
°C/W
°C/W
AD7124-4
Data Sheet
32
31
30
29
28
27
26
25
CS
CLK
SCLK
DIN
DOUT/RDY
SYNC
AVDD
PSW
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
1
2
3
4
5
6
7
8
AD7124-4
TOP VIEW
(Not to Scale)
24
23
22
21
20
19
18
17
REGCAPA
AVSS
REFOUT
AIN7/IOUT/VBIAS/REFIN2(–)
AIN6/IOUT/VBIAS/REFIN2(+)
DNC
DNC
AIN5/IOUT/VBIAS
DIN 1
24
SCLK 2
23
SYNC
CLK 3
22
AVDD
CS 4
9
10
11
12
13
14
15
16
REGCAPD 5
AIN3/IOUT/VBIAS/P2
DNC
DNC
REFIN1(+)
REFIN1(–)
DNC
DNC
AIN4/IOUT/VBIAS
IOVDD 6
13197-009
NOTES
1. DNC = DO NOT CONNECT.
2. CONNECT EXPOSED PAD TO AVSS.
AD7124-4
TOP VIEW
(Not to Scale)
DOUT/RDY
21
PSW
20
REGCAPA
19
AVSS
DGND 7
18
REFOUT
AIN0/IOUT/VBIAS 8
17
AIN7/IOUT/VBIAS/REFIN2(–)
AIN1/IOUT/VBIAS 9
16
AIN6/IOUT/VBIAS/REFIN2(+)
AIN2/IOUT/VBIAS/P1 10
15
AIN5/IOUT/VBIAS
AIN3/IOUT/VBIAS/P2 11
14
AIN4/IOUT/VBIAS
REFIN1(+) 12
13
REFIN1(–)
13197-300
REGCAPD
IOVDD
DGND
AIN0/IOUT/VBIAS
AIN1/IOUT/VBIAS
DNC
DNC
AIN2/IOUT/VBIAS/P1
Figure 10. 24-Lead TSSOP Pin Configuration
Figure 9. 32-Lead LFCSP Pin Configuration
Table 6. Pin Function Descriptions
LFCSP
1
2
Pin No.
TSSOP
5
6
Mnemonic
REGCAPD
IOVDD
3
4
7
8
DGND
AIN0/IOUT/VBIAS
5
9
AIN1/IOUT/VBIAS
6, 7, 10,
11, 14, 15,
18, 19
8
N/A1
DNC
10
AIN2/IOUT/VBIAS/P1
9
11
AIN3/IOUT/VBIAS/P2
Description
Digital LDO Regulator Output. Decouple this pin to DGND with a 0.1 µF capacitor.
Serial Interface Supply Voltage, 1.65 V to 3.6 V. IOVDD is independent of AVDD. Therefore,
the serial interface can operate at 1.65 V with AVDD at 3.6 V, for example.
Digital Ground Reference Point.
Analog Input 0/Output of Internal Excitation Current Source/Bias Voltage. This input pin is
configured via the configuration registers to be the positive or negative terminal of a
differential or pseudo differential input. Alternatively, the internal programmable excitation
current source can be made available at this pin. Either IOUT0 or IOUT1 can be switched to
this output. A bias voltage midway between the analog power supply rails can be generated
at this pin.
Analog Input 1/Output of Internal Excitation Current Source/Bias Voltage. This input pin is
configured via the configuration registers to be the positive or negative terminal of a
differential or pseudo differential input. Alternatively, the internal programmable excitation
current source can be made available at this pin. Either IOUT0 or IOUT1 can be switched to
this output. A bias voltage midway between the analog power supply rails can be generated
at this pin.
Do Not Connect. Do not connect to these pins.
Analog Input 2/Output of Internal Excitation Current Source/Bias Voltage/GeneralPurpose Output 1. This input pin is configured via the configuration registers to be the
positive or negative terminal of a differential or pseudo differential input. Alternatively,
the internal programmable excitation current source can be made available at this pin.
Either IOUT0 or IOUT1 can be switched to this output. A bias voltage midway between the
analog power supply rails can be generated at this pin. This pin can also be configured as a
general-purpose output bit, referenced between AVSS and AVDD.
Analog Input 3/Output of Internal Excitation Current Source/Bias Voltage/GeneralPurpose Output 2. This input pin is configured via the configuration registers to be the
positive or negative terminal of a differential or pseudo differential input. Alternatively,
the internal programmable excitation current source can be made available at this pin.
Either IOUT0 or IOUT1 can be switched to this output. A bias voltage midway between the
analog power supply rails can be generated at this pin. This pin can also be configured as a
general-purpose output bit, referenced between AVSS and AVDD.
Rev. A | Page 14 of 90
Data Sheet
LFCSP
12
Pin No.
TSSOP
12
AD7124-4
Mnemonic
REFIN1(+)
13
13
REFIN1(−)
16
14
AIN4/IOUT/VBIAS
17
15
AIN5/IOUT/VBIAS
20
16
AIN6/IOUT/VBIAS/
REFIN2(+)
21
17
AIN7/IOUT/VBIAS/
REFIN2(−)
22
18
REFOUT
23
19
AVSS
24
25
26
27
20
21
22
23
REGCAPA
PSW
AVDD
SYNC
28
24
DOUT/RDY
Description
Positive Reference Input. An external reference can be applied between REFIN1(+) and
REFIN1(−). REFIN1(+) can be anywhere between AVDD and AVSS + 1 V. The nominal
reference voltage (REFIN1(+) − REFIN1(−)) is 2.5 V, but the device functions with a
reference from 1 V to AVDD.
Negative Reference Input. This reference input can be anywhere between AVSS and AVDD −
1 V.
Analog Input 4/Output of Internal Excitation Current Source/Bias Voltage. This input pin is
configured via the configuration registers to be the positive or negative terminal of a
differential or pseudo differential input. Alternatively, the internal programmable excitation
current source can be made available at this pin. Either IOUT0 or IOUT1 can be switched to
this output. A bias voltage midway between the analog power supply rails can be generated
at this pin.
Analog Input 5/Output of Internal Excitation Current Source/Bias Voltage. This input pin is
configured via the configuration registers to be the positive or negative terminal of a
differential or pseudo differential input. Alternatively, the internal programmable excitation
current source can be made available at this pin. Either IOUT0 or IOUT1 can be switched to
this output. A bias voltage midway between the analog power supply rails can be generated
at this pin.
Analog Input 6/Output of Internal Excitation Current Source/Bias Voltage/Positive
Reference Input. This input pin is configured via the configuration registers to be the
positive or negative terminal of a differential or pseudo differential input. Alternatively,
the internal programmable excitation current source can be made available at this pin.
Either IOUT0 or IOUT1 can be switched to this output. A bias voltage midway between the
analog power supply rails can be generated at this pin. This pin also functions as a positive
reference input for REFIN2(±). REFIN2(+) can be anywhere between AVDD and AVSS + 1 V.
The nominal reference voltage (REFIN2(+) to REFIN2(−)) is 2.5 V, but the device functions with
a reference from 1 V to AVDD.
Analog Input 7/Output of Internal Excitation Current Source/Bias Voltage/Negative
Reference Input. This input pin is configured via the configuration registers to be the
positive or negative terminal of a differential or pseudo differential input. Alternatively,
the internal programmable excitation current source can be made available at this pin.
Either IOUT0 or IOUT1 can be switched to this output. A bias voltage midway between the
analog power supply rails can be generated at this pin. This pin also functions as the
negative reference input for REFIN2(±). This reference input can be anywhere between AVSS
and AVDD − 1 V.
Internal Reference Output. The buffered output of the internal 2.5 V voltage reference is
available on this pin.
Analog Supply Voltage. The voltage on AVDD is referenced to AVSS. The differential
between AVDD and AVSS must be between 2.7 V and 3.6 V in mid or low power mode and
between 2.9 V and 3.6 V in full power mode. AVSS can be taken below 0 V to provide a dual
power supply to the AD7124-4. For example, AVSS can be tied to −1.8 V and AVDD can be
tied to +1.8 V, providing a ±1.8 V supply to the ADC.
Analog LDO Regulator Output. Decouple this pin to AVSS with a 0.1 µF capacitor.
Low-Side Power Switch to AVSS.
Analog Supply Voltage, Relative to AVSS.
Synchronization Input. This pin is a logic input that allows synchronization of the digital
filters and analog modulators when using a number of AD7124-4 devices. When SYNC is
low, the nodes of the digital filter, the filter control logic, and the calibration control logic
are reset, and the analog modulator is held in a reset state. SYNC does not affect the digital
interface but does reset RDY to a high state if it is low.
Serial Data Output/Data Ready Output. DOUT/RDY functions as a serial data output pin to
access the output shift register of the ADC. The output shift register can contain data from
any of the on-chip data or control registers. In addition, DOUT/RDY operates as a data ready
pin, going low to indicate the completion of a conversion. If the data is not read after the
conversion, the pin goes high before the next update occurs. The DOUT/RDY falling edge
can also be used as an interrupt to a processor, indicating that valid data is available. With
an external serial clock, the data can be read using the DOUT/RDY pin. When CS is low, the
data/control word information is placed on the DOUT/RDY pin on the SCLK falling edge
and is valid on the SCLK rising edge.
Rev. A | Page 15 of 90
AD7124-4
LFCSP
29
Pin No.
TSSOP
1
Data Sheet
Mnemonic
DIN
30
2
SCLK
31
3
CLK
32
4
CS
EP
1
Description
Serial Data Input to the Input Shift Register on the ADC. Data in the input shift register is
transferred to the control registers within the ADC, with the register selection bits of the
communications register identifying the appropriate register.
Serial Clock Input. This serial clock input is for data transfers to and from the ADC. The SCLK pin
has a Schmitt-triggered input, making the interface suitable for opto-isolated applications. The
serial clock can be continuous with all data transmitted in a continuous train of pulses.
Alternatively, it can be a noncontinuous clock with the information being transmitted to
or from the ADC in smaller batches of data.
Clock Input/Clock Output. The internal clock can be made available at this pin.
Alternatively, the internal clock can be disabled, and the ADC can be driven by an external
clock. This allows several ADCs to be driven from a common clock, allowing simultaneous
conversions to be performed.
Chip Select Input. This is an active low logic input that selects the ADC. Use CS to select the
ADC in systems with more than one device on the serial bus or as a frame synchronization
signal in communicating with the device. CS can be hardwired low if the serial peripheral
interface (SPI) diagnostics are unused, allowing the ADC to operate in 3-wire mode with
SCLK, DIN, and DOUT interfacing with the device.
Exposed Pad. Connect the exposed pad to AVSS.
N/A means not applicable.
Rev. A | Page 16 of 90
0
CODES (HEX)
0
Figure 11. Noise Histogram Plot (Full Power Mode, Post Filter, Output Data
Rate = 25 SPS, Gain = 1)
400
Figure 12. Noise Histogram Plot (Mid Power Mode, Post Filter, Output Data
Rate = 25 SPS, Gain = 1)
200
150
Figure 13. Noise Histogram Plot (Low Power Mode, Post Filter, Output Data
Rate = 25 SPS, Gain = 1)
10,000 SAMPLES
400
1000
800
200
0
CODES (HEX)
10,000 SAMPLES
400
350
350
300
300
250
250
100
50
0
CODES (HEX)
Rev. A | Page 17 of 90
13197-011
CODES (HEX)
13197-013
500
7FFFE9
7FFFFA
800002
800009
800011
800019
800020
800028
800030
800038
80003F
800047
80004F
800057
80005E
800066
80006E
800075
80007D
800085
80008D
800094
80009C
8000A4
1000
OCCURRENCE
2000
8388394.0
8388452.8
8388469.6
8388486.4
8388503.2
8388520.0
8388536.8
8388553.6
8388570.4
8388587.2
8388604.0
8388620.8
8388637.6
8388654.4
8388671.2
8388688.0
8388704.8
8388721.6
8388738.4
8388755.2
8388772.0
8388788.8
8388805.6
600
OCCURRENCE
1500
350
13197-015
CODES (HEX)
13197-010
7FFFDC
7FFFDB
7FFFDA
7FFFD9
7FFFD8
7FFFD7
7FFFD6
7FFFD5
7FFFD4
7FFFD3
7FFFD2
7FFFD1
7FFFD0
7FFFCF
OCCURRENCE
10,000 SAMPLES
7FFEED
7FFF03
7FFF1A
7FFF30
7FFF47
7FFF5D
7FFF74
7FFF8A
7FFFA1
7FFFB8
7FFFCE
7FFFE5
7FFFFB
800012
800028
80003F
800055
80006C
800083
800099
8000B0
8000C6
8000DD
8000F3
80010A
800121
400
OCCURRENCE
0
13197-012
CODES (HEX)
13197-013
1200
7FFFCE
0
7FFFC6
7FFFC7
7FFFC8
7FFFC9
7FFFCA
7FFFCB
7FFFCC
7FFFCD
7FFFCE
7FFFCF
7FFFD0
7FFFD1
7FFFD2
7FFFD3
7FFFD4
7FFFD5
7FFFD6
7FFFD7
7FFFD8
7FFFD9
7FFFDA
7FFFDB
7FFFDC
7FFFDD
7FFFDE
7FFFDF
7FFFE0
7FFFE1
7FFFE2
7FFFE3
OCCURRENCE
TYPICAL PERFORMANCE CHARACTERISTICS
2500
8388394.0
8388452.8
8388469.6
8388486.4
8388503.2
8388520.0
8388536.8
8388553.6
8388570.4
8388587.2
8388604.0
8388620.8
8388637.6
8388654.4
8388671.2
8388688.0
8388704.8
8388721.6
8388738.4
8388755.2
8388772.0
8388788.8
8388805.6
OCCURRENCE
Data Sheet
AD7124-4
10,000 SAMPLES
300
250
200
150
100
50
Figure 14. Noise Histogram Plot (Full Power Mode, Post Filter, Output Data
Rate = 25 SPS, Gain = 128)
350
10,000 SAMPLES
300
250
200
150
100
50
Figure 15. Noise Histogram Plot (Mid Power Mode, Post Filter, Output Data
Rate = 25 SPS, Gain = 128)
10,000 SAMPLES
200
150
100
50
Figure 16. Noise Histogram Plot (Low Power Mode, Post Filter, Output Data
Rate = 25 SPS, Gain = 128)
AD7124-4
60
28 UNITS
40
OFFSET ERROR (µV)
20
0
–20
–40
5
20
35
50
65
80
95
110
–60
–40
–10
5
20
35
50
65
80
95
110
Figure 20. Input Referred Offset Error vs. Temperature (Gain = 16,
Full Power Mode)
60
28 UNITS
40
28 UNITS
40
OFFSET ERROR (µV)
OFFSET ERROR (µV)
–25
TEMPERATURE (°C)
Figure 17. Input Referred Offset Error vs. Temperature (Gain = 8,
Full Power Mode)
20
0
–20
–40
20
0
–20
–40
–25
–10
5
20
35
50
65
80
95
110
TEMPERATURE (°C)
–60
–40
13197-017
–60
–40
–10
5
20
35
50
65
80
95
110
Figure 21. Input Referred Offset Error vs. Temperature (Gain = 16,
Mid Power Mode)
60
28 UNITS
40
28 UNITS
OFFSET ERROR (µV)
40
20
0
–20
–40
20
0
–20
–40
–25
–10
5
20
35
50
65
80
95
110
TEMPERATURE (°C)
13197-018
–60
–40
–25
TEMPERATURE (°C)
Figure 18. Input Referred Offset Error vs. Temperature (Gain = 8,
Mid Power Mode)
OFFSET ERROR (µV)
–20
13197-019
–10
13197-016
–25
TEMPERATURE (°C)
60
0
–40
–60
–40
60
20
13197-020
OFFSET ERROR (µV)
40
28 UNITS
Figure 19. Input Referred Offset Error vs. Temperature (Gain = 8,
Low Power Mode)
–60
–40
–25
–10
5
20
35
50
65
80
95
110
TEMPERATURE (°C)
Figure 22. Input Referred Offset Error vs. Temperature (Gain = 16,
Low Power Mode)
Rev. A | Page 18 of 90
13197-021
60
Data Sheet
Data Sheet
60
AD7124-4
0.045
29 UNITS
30 UNITS
0.040
0.035
20
0.030
GAIN ERROR (%)
OFFSET ERROR (µV)
40
0
–20
0.025
0.020
0.015
0.010
0.005
–40
–25
–10
5
20
35
50
65
80
95
110
TEMPERATURE (°C)
–0.005
–40
13197-022
20
35
50
65
80
3
INL (PPM OF FSR)
0
0.0005
0.0010
110
1
0
–1
–2
–10
5
20
35
50
65
80
95
110
–3
–2.5
13197-023
–25
TEMPERATURE (°C)
0.015
–2.0
–1.5
–1.0
–0.5
0
0.5
1.0
1.5
2.0
2.5
ANALOG INPUT VOLTAGE × GAIN (V)
Figure 24. Input Referred Gain Error vs. Temperature (Gain = 1)
Figure 27. INL vs. Differential Input Signal (Analog Input × Gain),
ODR = 50 SPS, External 2.5 V Reference
4
30 UNITS
GAIN = 1
GAIN = 8
GAIN = 16
3
0.010
INL (ppm of FSR)
2
0.005
0
1
0
–1
–2
–0.005
–0.010
–40
–25
–10
5
20
35
50
65
80
95
110
TEMPERATURE (°C)
–4
–2.5
–1.5
–0.5
0.5
1.5
2.5
ANALOG INPUT VOLTAGE × GAIN (V)
Figure 28. INL vs. Differential Input Signal (Analog Input × Gain),
ODR = 50 SPS, Internal Reference
Figure 25. Input Referred Gain Error vs. Temperature (Gain = 8)
Rev. A | Page 19 of 90
13197-227
–3
13197-024
GAIN ERROR (%)
95
GAIN = 1
GAIN = 8
GAIN = 16
2
0.0005
GAIN ERROR (%)
5
Figure 26. Input Referred Gain Error vs. Temperature (Gain = 16)
30 UNITS
0.0015
–40
–10
TEMPERATURE (°C)
Figure 23. Input Referred Offset Error vs. Temperature (Gain = 1, Analog
Input Buffers Enabled)
0.0010
–25
13197-026
–60
–40
13197-025
0
AD7124-4
25
Data Sheet
30
109 UNITS
25
OCCURRENCE
15
10
5
10
13197-031
–0.85035
–0.76635
–0.79435
–0.82235
–0.85035
–0.87835
–0.90635
–0.93435
490
28 UNITS
EXCITATION CURRENT (µA)
485
2.500
2.499
2.498
2.497
2.496
480
475
470
465
10
35
60
85
110
TEMPERATURE (°C)
460
–40
0
EXCITATION CURRENT MISMATCH (%)
20
15
10
5
35
50
65
80
95
110
95
110
–2.534660
EXCITATION CURRENT ACCURACY (%)
–0.2
–0.4
–0.6
–0.8
–1.0
–25
–10
5
20
35
50
65
80
TEMPERATURE (°C)
13197-030
–2.707408
–3.880156
–3.052904
–3.225652
–3.398400
–3.571148
–3.743986
20
29 UNITS
–1.2
–40
0
–3.916644
5
Figure 33. Excitation Current Drift (500 µA)
109 UNITS
–4.089392
–10
TEMPERATURE (°C)
Figure 30. Internal Reference Voltage vs. Temperature
–4.262140
29 UNITS
–25
Figure 34. Excitation Current Drift Matching (500 µA)
Figure 31. IOUTx Current Initial Accuracy Histogram (500 µA)
Rev. A | Page 20 of 90
13197-033
–15
13197-028
2.494
–40
13197-032
2.495
OCCURRENCE
–0.96235
EXCITATION CURRENT MATCHING (%)
Figure 32. IOUTx Current Initial Matching Histogram (500 µA)
2.501
25
–0.99035
13197-027
2.500671
2.500471
2.500272
2.500073
2.499874
2.499675
2.499476
2.499277
2.499078
2.498879
2.498680
0
INITIAL ACCURACY (V)
INTERNAL REFERENCE VOLTAGE (V)
15
5
Figure 29. Internal Reference Voltage Histogram
2.502
20
–1.01835
COUNTS
20
0
109 UNITS
AD7124-4
1.0
450
0.9
400
0.8
0.6
0.5
0.4
0.3
50µA
100µA
250µA
500µA
750µA
1mA
0.2
0.1
0
0
0.33
0.66
0.99 1.32
1.65
1.98
2.31
2.64
2.97 3.30
200
150
100
0
–40
GAIN = 1, AIN BUFFERS OFF
GAIN = 2 TO 8
GAIN = 1, AIN BUFFERS ON
GAIN = 16 TO 128
–25
–10
5
20
35
50
65
80
95
110
TEMPERATURE (°C)
Figure 35. Output Compliance (AVDD = 3.3 V)
Figure 38. Analog Current vs. Temperature (Mid Power Mode)
300
1.000
0.995
250
0.985
0.980
0.975
0.970
50µA
100µA
250µA
500µA
750µA
0.960
0.955
0.950
0
0.33
0.66
0.99 1.32
1.65
1.98
2.31
2.64
2.97 3.30
0
–40
DIGITAL CURRENT (µA)
400
35
50
65
80
95
110
TEMPERATURE (°C)
13197-036
20
20
35
50
65
80
95
110
40
30
20
10
200
5
5
50
600
–10
–10
60
GAIN = 1, AIN BUFFERS OFF
GAIN = 2 TO 8
GAIN = 1, AIN BUFFERS ON
GAIN = 16 TO 128
–25
–25
Figure 39. Analog Current vs. Temperature (Low Power Mode)
800
0
–40
GAIN = 1, AIN BUFFERS OFF
GAIN = 2 TO 8
GAIN = 1, AIN BUFFERS ON
GAIN = 16 TO 128
TEMPERATURE (°C)
Figure 36. Output Compliance (AVDD = 3.3 V)
1000
100
50
VLOAD (V)
1200
150
Figure 37. Analog Current vs. Temperature (Full Power Mode)
0
–40
FULL POWER
MID POWER
LOW POWER
–25
–10
5
20
35
50
65
80
TEMPERATURE (°C)
Figure 40. Digital Current vs. Temperature
Rev. A | Page 21 of 90
95
110
13197-039
0.965
200
13197-038
ANALOG CURRENT (µA)
0.990
13197-035
EXCITATION CURRENT (NORMALIZED)
250
50
VLOAD (V)
ANALOG CURRENT (µA)
300
13197-037
ANALOG CURRENT (µA)
350
0.7
13197-034
EXCITATION CURRENT (NORMALIZED)
Data Sheet
Data Sheet
6
4
4
3
2
2
0
1
0
CURRENT (nA)
–2
–4
–6
–1
–2
–3
–8
–12
–14
–40
–4
GAIN = 1
GAIN = 4
GAIN = 16
GAIN = 64
–20
GAIN = 2
GAIN = 8
GAIN = 32
GAIN = 128
0
20
40
–5
–6
60
80
100
TEMPERATURE (°C)
–7
–40
13197-040
–10
Figure 41. Absolute Analog Input Current vs. Temperature (Full Power Mode)
GAIN = 2
GAIN = 8
GAIN = 32
GAIN = 128
GAIN = 1
GAIN = 4
GAIN = 16
GAIN = 64
0
–20
20
40
60
80
100
TEMPERATURE (°C)
13197-041
CURRENT (nA)
AD7124-4
Figure 44. Differential Analog Input Current vs. Temperature (Full Power Mode)
2
2
1
0
CURRENT (nA)
CURRENT (nA)
0
–2
–4
–6
–1
–2
–3
–4
0
20
40
–5
60
80
100
TEMPERATURE (°C)
–6
–40
0
40
60
80
100
0
–1
CURRENT (nA)
–2
CURRENT (nA)
20
1
–1
–3
–4
–5
–6
–2
–3
–4
GAIN = 1
GAIN = 4
GAIN = 16
GAIN = 64
–20
GAIN = 2
GAIN = 8
GAIN = 32
GAIN = 128
0
20
40
TEMPERATURE (°C)
–5
60
80
100
–6
–40
13197-044
–9
–40
0
Figure 45. Differential Analog Input Current vs. Temperature (Mid Power Mode)
1
–8
–20
GAIN = 2
GAIN = 8
GAIN = 32
GAIN = 128
TEMPERATURE (°C)
Figure 42. Absolute Analog Input Current vs. Temperature (Mid Power Mode)
–7
GAIN = 1
GAIN = 4
GAIN = 16
GAIN = 64
13197-043
–20
GAIN = 2
GAIN = 8
GAIN = 32
GAIN = 128
GAIN = 1
GAIN = 4
GAIN = 16
GAIN = 64
–20
GAIN = 2
GAIN = 8
GAIN = 32
GAIN = 128
0
20
40
TEMPERATURE (°C)
Figure 43. Absolute Analog Input Current vs. Temperature (Low Power Mode)
60
80
100
13197-045
–10
–40
GAIN = 1
GAIN = 4
GAIN = 16
GAIN = 64
13197-042
–8
Figure 46. Differential Analog Input Current vs. Temperature (Low Power Mode)
Rev. A | Page 22 of 90
Data Sheet
AD7124-4
0
23
22
–1.5
FULL POWER
MID POWER
LOW POWER
–2.5
–3.0
–3.5
0
20
40
60
80
100
Figure 47. Reference Input Current vs. Temperature (Reference Buffers Enabled)
16
15
G
G
G
G
G
G
G
G
G
14
13
12
1
PEAK-TO-PEAK RESOLUTION (Bits)
0.6
0.4
0.2
0
–0.2
–0.4
40 50
60
70 85
95 105
TEMPERATURE (°C)
10k
21
20
19
18
17
16
15
G
G
G
G
G
G
G
G
G
14
13
12
11
25
1k
22
0.8
15
100
23
1.0
0
10
Figure 50. Peak-to-Peak Resolution vs. Output Data Rate (Settled), Sinc3 Filter
(Full Power Mode)
32 UNITS
–40 –30 –20 –10
= 1 BUFF OFF
=1
=2
=4
=8
= 16
= 32
= 64
= 128
OUTPUT DATA RATE, SETTLED (SPS)
10
13197-047
TEMPERATURE SENSOR ERROR (°C)
1.2
Figure 48. Temperature Sensor Accuracy
1
= 1 BUFF OFF
=1
=2
=4
=8
= 16
= 32
= 64
= 128
10
100
1k
10k
OUTPUT DATA RATE (SPS)
Figure 51. Peak-to-Peak Resolution vs. Output Data Rate, Sinc4 + Sinc1 Filter
(Full Power Mode)
23
23
22
22
PEAK-TO-PEAK RESOLUTION (Bits)
21
20
19
18
17
16
15
G
G
G
G
G
G
G
G
G
14
13
12
11
1
= 1 BUFF OFF
=1
=2
=4
=8
= 16
= 32
= 64
= 128
10
21
20
19
18
17
16
15
G
G
G
G
G
G
G
G
G
14
13
12
11
100
1k
OUTPUT DATA RATE, SETTLED (SPS)
10k
10
13197-048
PEAK-TO-PEAK RESOLUTION (Bits)
17
10
13197-046
–20
TEMPERATURE (°C)
10
18
11
–4.0
–40
–0.6
19
13197-050
–2.0
20
Figure 49. Peak-to-Peak Resolution vs. Output Data Rate (Settled), Sinc4 Filter
(Full Power Mode)
1
= 1 BUFF OFF
=1
=2
=4
=8
= 16
= 32
= 64
= 128
10
100
OUTPUT DATA RATE (SPS)
1k
10k
13197-051
CURRENT (nA)
–1.0
21
13197-049
PEAK-TO-PEAK RESOLUTION (Bits)
–0.5
Figure 52. Peak-to-Peak Resolution vs. Output Data Rate, Sinc3 + Sinc1 Filter
(Full Power Mode)
Rev. A | Page 23 of 90
Data Sheet
23
22
22
21
21
18
17
16
15
G
G
G
G
G
G
G
G
G
14
13
12
11
10
= 1 BUFF OFF
=1
=2
=4
=8
= 16
= 32
= 64
= 128
10
1
100
1k
10k
100k
Figure 53. Peak-to-Peak Resolution vs. Output Data Rate (Settled), Sinc4 Filter
(Mid Power Mode)
18
17
16
15
13
12
22
21
21
PEAK-TO-PEAK RESOLUTION (Bits)
23
19
18
17
16
G
G
G
G
G
G
G
G
G
14
13
12
11
10
1
= 1 BUFF OFF
=1
=2
=4
=8
= 16
= 32
= 64
= 128
10
1k
10k
100k
OUTPUT DATA RATE, SETTLED (SPS)
Figure 54. Peak-to-Peak Resolution vs. Output Data Rate (Settled), Sinc3 Filter
(Mid Power Mode)
18
17
16
15
13
12
10
21
PEAK-TO-PEAK RESOLUTION (Bits)
22
17
16
13
12
11
10
1
= 1 BUFF OFF
=1
=2
=4
=8
= 16
= 32
= 64
= 128
10
100
OUTPUT DATA RATE (SPS)
1k
Figure 55. Peak-to-Peak Resolution vs. Output Data Rate, Sinc4 + Sinc1 Filter
(Mid Power Mode)
100
1k
10k
20
19
18
17
16
15
G
G
G
G
G
G
G
G
G
14
13
12
11
10
9
13197-054
G
G
G
G
G
G
G
G
G
14
10
Figure 57. Peak-to-Peak Resolution vs. Output Data Rate (Settled), Sinc4 Filter
(Low Power Mode)
21
18
1
= 1 AIN BUFF OFF
=1
=2
=4
=8
= 16
= 32
= 64
= 128
OUTPUT DATA RATE, SETTLED (SPS)
23
15
G
G
G
G
G
G
G
G
G
14
22
19
1k
19
23
20
100
20
11
100
10
1
Figure 56. Peak-to-Peak Resolution vs. Output Data Rate, Sinc3 + Sinc1 Filter
(Mid Power Mode)
22
20
= 1 BUFF OFF
=1
=2
=4
=8
= 16
= 32
= 64
= 128
OUTPUT DATA RATE (SPS)
23
15
G
G
G
G
G
G
G
G
G
14
10
13197-053
PEAK-TO-PEAK RESOLUTION (Bits)
19
11
OUTPUT DATA RATE, SETTLED (SPS)
PEAK-TO-PEAK RESOLUTION (Bits)
20
13197-056
19
1
= 1 AIN BUFF OFF
=1
=2
=4
=8
= 16
= 32
= 64
= 128
10
100
1k
OUTPUT DATA RATE, SETTLED (SPS)
10k
13197-057
20
13197-055
PEAK-TO-PEAK RESOLUTION (Bits)
23
13197-052
PEAK-TO-PEAK RESOLUTION (Bits)
AD7124-4
Figure 58. Peak-to-Peak Resolution vs. Output Data Rate (Settled), Sinc3 Filter
(Low Power Mode)
Rev. A | Page 24 of 90
Data Sheet
AD7124-4
35
23
GAIN = 1, LOW POWER
GAIN = 1, MID POWER
GAIN = 1, FULL POWER
GAIN = 8, LOW POWER
GAIN = 8, MID POWER
GAIN = 8, FULL POWER
GAIN = 16, LOW POWER
GAIN = 16, MID POWER
GAIN = 16, FULL POWER
30
21
DIGITAL CURRENT (µA)
20
19
18
17
16
13
12
11
1
15
10
5
10
100
1k
OUTPUT DATA RATE (SPS)
0
Figure 59. Peak-to-Peak Resolution vs. Output Data Rate, Sinc4 + Sinc1 Filter
(Low Power Mode)
0
1000
800
20
RMS NOISE (nV)
16
15
G
G
G
G
G
G
G
G
G
14
13
12
11
10
= 1 BUFF OFF
=1
=2
=4
=8
= 16
= 32
= 64
= 128
1
10
100
1k
Figure 60. Peak-to-Peak Resolution vs. Output Data Rate, Sinc3 + Sinc1 Filter
(Low Power Mode)
400
0.6
0.7
0.8
0.9
1.0
LOW POWER, EXTERNAL REF
MID POWER, EXTERNAL REF
FULL POWER, EXTERNAL REF
LOW POWER INTERNAL REF
MID POWER, INTERNAL REF
FULL POWER, INTERNAL REF
400
250
–0.06
–0.04
–0.02
0
0.02
0.04
0.06
0.08
ANALOG INPUT VOLTAGE (V)
Figure 63. RMS Noise vs. Analog Input Voltage for the Internal Reference and
External Reference (Gain = 32, 50 SPS)
29 UNITS
3
OSCILLATOR ERROR (%)
300
0
–0.08
4
GAIN = 1, LOW POWER
GAIN = 1, MID POWER
GAIN = 1, FULL POWER
GAIN = 8, LOW POWER
GAIN = 8, MID POWER
GAIN = 8, FULL POWER
GAIN = 16, LOW POWER
GAIN = 16, MID POWER
GAIN = 16, FULL POWER
350
ANALOG CURRENT (µA)
0.5
200
OUTPUT DATA RATE (SPS)
200
150
2
1
0
–1
100
–2
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
WAIT TIME IN STANDBY MODE (Seconds)
0.9
1.0
13197-200
50
0
0.4
600
13197-059
PEAK-TO-PEAK RESOLUTION (Bits)
21
17
0.3
Figure 62. Digital Current vs. Wait Time in Standby Mode, ADC in Single
Conversion Mode (50 SPS)
22
18
0.2
WAIT TIME IN STANDBY MODE (Seconds)
23
19
0.1
Figure 61. Analog Current vs. Wait Time in Standby Mode, ADC in Single
Conversion Mode (50 SPS)
Rev. A | Page 25 of 90
–3
–40
–25
–10
5
20
35
50
65
80
95
TEMPERATURE (°C)
Figure 64. Internal Oscillator Error vs. Temperature
110
13197-029
10
= 1 BUFF OFF
=1
=2
=4
=8
= 16
= 32
= 64
= 128
13197-201
G
G
G
G
G
G
G
G
G
14
20
13197-202
15
25
13197-058
PEAK-TO-PEAK RESOLUTION (Bits)
22
AD7124-4
Data Sheet
TERMINOLOGY
AINM
AINM refers to the negative analog input.
Offset Error
Offset error is the deviation of the first code transition from the
ideal AINP voltage (AINM + 0.5 LSB) when operating in the
unipolar mode.
Integral Nonlinearity (INL)
INL is the maximum deviation of any code from a straight line
passing through the endpoints of the transfer function. The
endpoints of the transfer function are zero scale (not to be
confused with bipolar zero), a point 0.5 LSB below the first code
transition (000 … 000 to 000 … 001), and full scale, a point
0.5 LSB above the last code transition (111 … 110 to 111 …
111). The error is expressed in ppm of the full-scale range.
In bipolar mode, offset error is the deviation of the midscale
transition (0111 … 111 to 1000 … 000) from the ideal AINP
voltage (AINM − 0.5 LSB).
Offset Calibration Range
In the system calibration modes, the AD7124-4 calibrates offset
with respect to the analog input. The offset calibration range
specification defines the range of voltages that the AD7124-4
can accept and still calibrate offset accurately.
Gain Error
Gain error is the deviation of the last code transition (111 …
110 to 111 … 111) from the ideal AINP voltage (AINM +
VREF/gain − 3/2 LSBs). Gain error applies to both unipolar
and bipolar analog input ranges.
Full-Scale Calibration Range
The full-scale calibration range is the range of voltages that the
AD7124-4 can accept in the system calibration mode and still
calibrate full scale correctly.
AINP
AINP refers to the positive analog input.
Gain error is a measure of the span error of the ADC. It
includes full-scale errors but not zero-scale errors. For unipolar
input ranges, it is defined as full-scale error minus unipolar
offset error; whereas for bipolar input ranges it is defined as
full-scale error minus bipolar zero error.
Input Span
In system calibration schemes, two voltages applied in sequence
to the AD7124-4 analog input define the analog input range.
The input span specification defines the minimum and
maximum input voltages from zero to full scale that the
AD7124-4 can accept and still calibrate gain accurately.
Rev. A | Page 26 of 90
Data Sheet
AD7124-4
RMS NOISE AND RESOLUTION
in parentheses) is calculated based on peak-to-peak noise
(shown in parentheses). The peak-to-peak resolution represents
the resolution for which there is no code flicker.
Table 7 through Table 36 show the rms noise, peak-to-peak
noise, effective resolution, and noise-free (peak-to-peak)
resolution of the AD7124-4 for various output data rates, gain
settings, and filters. The numbers given are for the bipolar input
range with an external 2.5 V reference. These numbers are
typical and are generated with a differential input voltage of 0 V
when the ADC is continuously converting on a single channel.
It is important to note that the effective resolution is calculated
using the rms noise, whereas the peak-to-peak resolution (shown
Effective Resolution = Log2(Input Range/RMS Noise)
Peak-to-Peak Resolution = Log2(Input Range/Peak-to-Peak
Noise
FULL POWER MODE
Sinc4
Table 7. RMS Noise (Peak-to-Peak Noise) vs. Gain and Output Data Rate (µV), Full Power Mode
Filter
Word
(Dec.)
2047
1920
960
480
384
320
240
120
60
30
15
8
4
2
1
Output
Data
Rate
(SPS)
9.4
10
20
40
50
60
80
160
320
640
1280
2400
4800
9600
19,200
Output Data
Rate (Zero
Latency
Mode) (SPS)
2.34
2.5
5
10
12.5
15
20
40
80
160
320
600
1200
2400
4800
f3dB
(Hz)
2.16
2.3
4.6
9.2
11.5
13.8
18.4
36.8
73.6
147.2
294.4
552
1104
2208
4416
Gain = 1
0.24 (1.5)
0.23 (1.5)
0.31 (2.1)
0.42 (3)
0.48 (3.2)
0.51 (3.3)
0.6 (4.8)
0.86 (6.9)
1.2 (8.9)
1.7 (13)
2.4 (19)
3.3 (25)
4.9 (38)
8.8 (76)
72 (500)
Gain = 2
0.15 (0.89)
0.14 (0.89)
0.22 (1.3)
0.3 (2.1)
0.33 (2.1)
0.35 (2.4)
0.41 (3)
0.55 (4.1)
0.76 (6.1)
1.1 (8.8)
1.6 (13)
2.3 (16)
3.4 (25)
6.8 (61)
38 (270)
Gain = 4
0.091 (0.6)
0.094 (0.6)
0.13 (0.89)
0.19 (1.4)
0.2 (1.3)
0.23 (1.3)
0.28 (1.8)
0.37 (2.5)
0.53 (4.1)
0.74 (5.7)
1.1 (8.4)
1.5 (12)
2.4 (20)
4.9 (34)
21 (150)
Gain = 8
0.071 (0.41)
0.076 (0.42)
0.1 (0.6)
0.14 (0.97)
0.16 (1.1)
0.17 (1.2)
0.19 (1.3)
0.29 (2)
0.4 (2.7)
0.57 (4.1)
0.82 (6)
1.2 (8)
2 (13)
4.3 (27)
13 (95)
Gain = 16
0.045 (0.26)
0.048 (0.27)
0.069 (0.41)
0.09 (0.63)
0.1 (0.75)
0.11 (0.78)
0.13 (0.86)
0.2 (1.2)
0.26 (1.8)
0.38 (2.9)
0.55 (4)
0.76 (6)
1.3 (9.1)
2.6 (21)
7.5 (57)
Gain = 32
0.031 (0.17)
0.03 (0.19)
0.044 (0.26)
0.063 (0.39)
0.068 (0.43)
0.077 (0.5)
0.09 (0.54)
0.13 (0.84)
0.18 (1.2)
0.26 (2)
0.38 (2.5)
0.53 (4)
0.83 (6.4)
1.7 (13)
4.4 (33)
Gain = 64
0.025 (0.15)
0.025 (0.16)
0.035 (0.22)
0.053 (0.34)
0.059 (0.42)
0.064 (0.41)
0.072 (0.48)
0.11 (0.7)
0.15 (0.95)
0.22 (1.6)
0.3 (2.3)
0.43 (3.2)
0.68 (4.8)
1.3 (12)
3.3 (26)
Gain = 128
0.023 (0.14)
0.025 (0.15)
0.034 (0.22)
0.043 (0.27)
0.048 (0.28)
0.056 (0.35)
0.063 (0.45)
0.098 (0.6)
0.14 (0.86)
0.19 (1.4)
0.26 (1.8)
0.37 (2.7)
0.58 (4.3)
1.2 (9.4)
2.8 (23)
Table 8. Effective Resolution (Peak-to-Peak Resolution) vs. Gain and Output Data Rate (Bits), Full Power Mode
Filter
Word
(Dec.)
2047
1920
960
480
384
320
240
120
60
30
15
8
4
2
1
Output
Data Rate
(SPS)
9.4
10
20
40
50
60
80
160
320
640
1280
2400
4800
9600
19,200
Output Data Rate
(Zero Latency
Mode) (SPS)
2.34
2.5
5
10
12.5
15
20
40
80
160
320
600
1200
2400
4800
Gain = 1
24 (21.7)
24 (21.7)
23.9 (21.2)
23.5 (20.7)
23.3 (20.5)
23.2 (20.3)
23 (20)
22.5 (19.5)
22 (19.1)
21.5 (18.5)
21 (18)
20.5 (17.5)
20 (17)
19.1 (16)
16.1 (13.3)
Gain = 2
24 (21.4)
24 (21.4)
23.5 (20.8)
23 (20.3)
22.9 (20.2)
22.8 (20)
22.6 (19.7)
22.1 (19.2)
21.6 (18.6)
21.1 (18.1)
20.5 (17.6)
20.1 (17.2)
19.5 (16.5)
18.5 (15.3)
16 (13.2)
Gain = 4
23.7 (21)
23.7 (21)
23.2 (20.4)
22.6 (19.8)
22.5 (19.6)
22.4 (19.5)
22.1 (19.3)
21.7 (18.9)
21.2 (18.2)
20.7 (17.7)
20.2 (17.2)
19.7 (16.7)
19 (16)
18 (15.1)
15.9 (13)
Rev. A | Page 27 of 90
Gain = 8
23.1 (20.5)
23 (20.5)
22.5 (20)
22.1 (19.3)
21.9 (19.1)
21.8 (19)
21.6 (18.9)
21 (18.3)
20.6 (17.8)
20.1 (17.2)
19.5 (16.7)
19 (16.2)
18.3 (15.6)
17.2 (14.5)
15.5 (12.7)
Gain = 16
22.7 (20.2)
22.6 (20.1)
22.1 (19.5)
21.7 (18.9)
21.5 (18.7)
21.4 (18.6)
21.2 (18.5)
20.6 (18)
20.2 (17.4)
19.7 (16.8)
19.1 (16.3)
18.6 (15.7)
17.9 (15.1)
16.9 (13.9)
15.4 (12.4)
Gain = 32
22.3 (19.8)
22.3 (19.7)
21.8 (19.2)
21.2 (18.6)
21.1 (18.5)
21 (18.3)
20.7 (18.1)
20.1 (17.5)
19.7 (17)
19.2 (16.3)
18.7 (15.9)
18.2 (15.3)
17.5 (14.6)
16.5 (13.5)
15.1 (12.2)
Gain = 64
21.6 (19)
21.6 (19)
21.1 (18.4)
20.5 (17.8)
20.4 (17.7)
20.2 (17.6)
20 (17.3)
19.5 (16.9)
19 (16.3)
18.5 (15.6)
18 (15.1)
17.5 (14.6)
16.8 (14)
15.9 (12.7)
14.6 (11.5)
Gain = 128
20.7 (18.1)
20.7 (18.1)
20.1 (19.4)
19.8 (17.1)
19.6 (17)
19.4 (16.6)
19.2 (16.4)
18.6 (16)
18.1 (15.5)
17.6 (14.8)
17.2 (14.4)
16.7 (13.8)
16 (13.2)
15 (12)
13.8 (10.8)
AD7124-4
Data Sheet
Sinc3
Table 9. RMS Noise (Peak-to-Peak Noise) vs. Gain and Output Data Rate (µV), Full Power Mode
Filter
Word
(Dec.)
2047
1920
1280
640
384
320
160
80
40
20
10
6
3
2
1
Output
Data
Rate
(SPS)
9.4
10
20
30
50
60
120
240
480
960
1920
3200
6400
9600
19,200
Output
Data Rate
(Zero
Latency
Mode)
(SPS)
3.13
3.33
5
10
16.67
20
40
80
160
320
640
1066.67
2133.33
3200
6400
f3dB
(Hz)
2.56
2.72
5.44
8.16
13.6
16.32
32.64
65.28
130.56
261.12
522.24
870.4
1740.8
2611.2
5222.4
Gain = 1
0.37 (1.5)
0.24 (1.5)
0.31 (1.8)
0.4 (2.6)
0.53 (3.3)
0.55 (3.6)
0.78 (5.1)
1.1 (7)
1.5 (11)
2.3 (16)
3.2 (26)
4.9 (38)
25 (170)
110 (820)
890 (6500)
Gain = 2
0.15 (0.89)
0.15 (0.89)
0.18 (1.2)
0.26 (1.6)
0.3 (2.2)
0.37 (2.4)
0.53 (3.4)
0.73 (4.9)
1.1 (6.8)
1.5 (9.8)
2.2 (16)
3.2 (24)
13 (89)
54 (390)
430 (3000)
Gain = 4
0.096 (0.58)
0.096 (0.6)
0.12 (0.82)
0.17 (1.2)
0.2 (1.6)
0.24 (1.8)
0.35 (2.3)
0.49 (3.2)
0.67 (4.5)
0.99 (6.6)
1.5 (11)
2.1 (15)
7.1 (54)
28 (210)
220 (1500)
Gain = 8
0.07 (0.38)
0.07 (0.4)
0.09 (0.55)
0.11 (0.82)
0.17 (1.1)
0.19 (1.3)
0.26 (1.8)
0.37 (2.6)
0.52 (3.7)
0.75 (5.1)
1.1 (8.5)
1.6 (12)
4.3 (35)
14 (110)
110 (790)
Gain = 16
0.046 (0.25)
0.05 (0.26)
0.059 (0.35)
0.088 (0.52)
0.1 (0.75)
0.12 (0.8)
0.17 (1.1)
0.25 (1.6)
0.34 (2.2)
0.53 (3.5)
0.73 (5.5)
1 (7.7)
2.4 (18)
7.4 (57)
55 (390)
Gain = 32
0.033 (0.16)
0.034 (0.17)
0.041 (0.24)
0.055 (0.36)
0.075 (0.51)
0.084 (0.54)
0.12 (0.85)
0.17 (1.2)
0.25 (1.7)
0.35 (2.4)
0.49 (3.9)
0.68 (5.6)
1.5 (11)
3.9 (27)
28 (190)
Gain = 64
0.023 (0.11)
0.023 (0.12)
0.033 (0.18)
0.048 (0.27)
0.062 (0.39)
0.068 (0.44)
0.1 (0.66)
0.14 (1)
0.19 (1.4)
0.28 (2.1)
0.4 (3.2)
0.56 (4.2)
1.1 (8.4)
2.3 (17)
14 (100)
Gain = 128
0.017 (0.09)
0.018 (0.09)
0.027 (0.14)
0.039 (0.22)
0.056 (0.33)
0.06 (0.37)
0.097 (0.55)
0.12 (0.78)
0.17 (1.2)
0.25 (1.8)
0.35 (2.7)
0.48 (3.6)
0.9 (6.7)
1.7 (13)
7.6 (56)
Table 10. Effective Resolution (Peak-to-Peak Resolution) vs. Gain and Output Data Rate, Full Power Mode
Filter
Word
(Dec.)
2047
1920
1280
640
384
320
160
80
40
20
10
6
3
2
1
Output
Data
Rate
(SPS)
9.4
10
20
30
50
60
120
240
480
960
1920
3200
6400
9600
19,200
Output Data
Rate (Zero
Latency Mode)
(SPS)
3.13
3.33
5
10
16.67
20
40
80
160
320
640
1066.67
2133.33
3200
6400
Gain = 1
24 (21.7)
24 (21.7)
24 (21.4)
23.6 (20.9)
23.2 (20.5)
23.1 (20.4)
22.6 (19.9)
22.1 (19.4)
21.6 (18.8)
21.1 (18.3)
20.6 (17.6)
19.9 (17)
17.6 (14.8)
15.5 (12.6)
12.5 (9.7)
Gain = 2
24 (21.4)
24 (21.4)
23.7 (21)
23.2 (20.5)
22.8 (20.1)
22.7 (20)
22.2 (19.5)
21.7 (19)
21.2 (18.5)
20.7 (18)
20.1 (17.2)
19.6 (16.6)
17.6 (14.8)
15.5 (12.6)
12.5 (9.7)
Gain = 4
23.6 (21)
23.6 (21)
23.2 (20.5)
22.8 (20)
22.4 (19.6)
22.3 (19.4)
21.8 (19)
21.3 (18.6)
20.8 (18.1)
20.3 (17.5)
19.7 (16.8)
19.2 (16.3)
17.4 (14.5)
15.4 (12.6)
12.5 (9.7)
Gain = 8
23.1 (20.6)
23.1 (20.6)
22.7 (20.1)
22.2 (19.5)
21.8 (19.1)
21.7 (18.9)
21.2 (18.4)
20.7 (17.9)
20.2 (17.4)
19.7 (16.9)
19.1 (16.2)
18.6 (15.6)
17.2 (14.1)
15.4 (12.5)
12.5 (9.6)
Gain = 16
22.7 (20.3)
22.6 (20.2)
22.3 (19.8)
21.8 (19.2)
21.4 (18.7)
21.3 (18.6)
20.8 (18.1)
20.3 (17.6)
19.8 (17.1)
19.2 (16.4)
18.7 (15.8)
18.2 (15.3)
17 (14.1)
15.4 (12.4)
12.5 (9.6)
Gain = 32
22.2 (19.9)
22.2 (19.8)
21.9 (19.3)
21.4 (18.7)
21 (18.2)
20.8 (18.1)
20.3 (17.5)
19.8 (17)
19.3 (16.5)
18.8 (16)
18.3 (15.3)
17.8 (14.8)
16.7 (13.8)
15.3 (12.5)
12.4 (9.6
Gain = 64
21.7 (19.3)
21.7 (19.3)
21.2 (18.7)
20.6 (18.1)
20.3 (17.6)
20.1 (17.4)
19.6 (26.9)
19.1 (16.3)
18.6 (15.8)
18.1 (15.2)
17.6 (14.6)
17.1 (14.2)
16.3 (13.2)
15 (12.2)
12.4 (9.6)
Gain = 128
21 (18.7)
21 (18.7)
20.5 (18.1)
19.9 (17.4)
19.4 (16.9)
19.3 (16.7)
18.7 (16.1)
18.3 (15.6)
17.8 (15)
17.3 (14.4)
16.8 (13.8)
16.3 (13.4)
15.4 (12.5)
14.5 (11.6)
12.3 (9.5)
Post Filters
Table 11. RMS Noise (Peak-to-Peak Noise) vs. Gain and Output Data Rate (µV), Full Power Mode
Output Data Rate (SPS)
16.67
20
25
27.27
Gain = 1
0.51 (3.3)
0.53 (3.3)
0.57 (3.6)
0.6 (3.9)
Gain = 2
0.34 (2.1)
0.36 (2.1)
0.37 (2.2)
0.38 (2.2)
Gain = 4
0.21 (1.3)
0.23 (1.3)
0.25 (1.6)
0.26 (1.6)
Gain = 8
0.16 (0.97)
0.18 (1)
0.18 (1.2)
0.19 (1.2)
Rev. A | Page 28 of 90
Gain = 16
0.11 (0.65)
0.11 (0.65)
0.12 (0.75)
0.13 (0.82)
Gain = 32
0.075 (0.41)
0.078 (0.45)
0.082 (0.47)
0.084 (0.55)
Gain = 64
0.062 (0.34)
0.062 (0.34)
0.062 (0.38)
0.072 (0.44)
Gain = 128
0.051(0.3)
0.051 (0.3)
0.055 (0.31)
0.063 (0.43)
Data Sheet
AD7124-4
Table 12. Effective Resolution (Peak-to-Peak Resolution) vs. Gain and Output Data Rate (Bits), Full Power Mode
Output Data Rate (SPS)
16.67
20
25
27.27
Gain = 1
23.2 (20.5)
23.2 (20.5)
23.1 (20.4)
23 (20.3)
Gain = 2
22.8 (20.2)
22.7 (20.2)
22.7 (20.1)
22.6 (20.1)
Gain = 4
22.5 (19.9)
22.3 (19.9)
22.2 (19.6)
22.2 (19.5)
Gain = 8
21.9 (19.3)
21.7 (19.2)
21.7 (19)
21.7 (19)
Gain = 16
21.5 (18.9)
21.5 (18.9)
21.3 (18.7)
21.2 (18.5)
Gain = 32
21 (18.5)
20.9 (18.4)
20.9 (18.3)
20.8 (18.1)
Gain = 64
20.3 (17.8)
20.3 (17.8)
20.3 (17.7)
20.1 (17.4)
Gain = 128
19.5 (17)
19.5 (17)
19.5 (17)
19.2 (16.5)
Fast Settling Filter (Sinc4 + Sinc1)
Table 13. RMS Noise (Peak-to-Peak Noise) vs. Gain and Output Data Rate (µV), Full Power Mode (Average by 16)
Filter
Word
(Dec.)
384
120
24
20
2
1
Output
Data Rate
(SPS)
2.63
8.42
42.11
50.53
505.26
1010.53
Gain = 1
0.19 (1.2)
0.32 (2.1)
0.69 (4.6)
0.71 (5.1)
2.4 (18)
4.8 (35)
Gain = 2
0.11 (0.75)
0.2 (1.3)
0.44 (3)
0.49 (3.1)
1.6 (10)
3 (20)
Gain = 4
0.077 (0.52)
0.13 (0.97)
0.29 (2.1)
0.3 (2.2)
1.1 (8.3)
1.9 (12)
Gain = 8
0.063 (0.34)
0.1 (0.63)
0.23 (1.6)
0.25 (1.7)
0.87 (5.5)
1.4 (8.8)
Gain = 16
0.036 (0.21)
0.067 (0.46)
0.14 (0.99)
0.16 (1.1)
0.56 (3.5)
0.89 (5.2)
Gain = 32
0.027 (0.17)
0.045 (0.28)
0.1 (0.72)
0.11 (0.78)
0.47 (2.9)
0.57 (3.7)
Gain = 64
0.021 (0.11)
0.039 (0.23)
0.081 (0.54)
0.09 (0.6)
0.33 (2.1)
0.49 (3)
Gain = 128
0.019 (0.098)
0.031 (0.2)
0.07 (0.49)
0.082 (0.57)
0.3 (2)
0.44 (3)
Table 14. Effective Resolution (Peak-to-Peak Resolution) vs. Gain and Output Data Rate (Bits), Full Power Mode (Average by 16)
Filter Word
(Dec.)
384
120
24
20
2
1
Output Data Rate
(SPS)
2.63
8.42
42.11
50.53
505.26
1010.53
Gain = 1
24 (22)
23.9 (21.2)
22.8 (20)
22.7 (19.9)
21 (18.1)
20 (17.1)
Gain = 2
24 (21.7)
23.6 (20.8)
22.4 (19.7)
22.3 (19.6)
20.6 (17.9)
19.7 (16.9)
Gain = 4
23.9 (21.2)
23.3 (20.3)
22.1 (19.2)
22 (19.1)
20.2 (17.2)
19.3 (16.6)
Gain = 8
23.3 (20.8)
22.5 (19.9)
21.4 (18.6)
21.2 (18.5)
19.5 (16.8)
18.8 (16.1)
Gain = 16
23 (20.5)
22.2 (19.4)
21.1 (18.3)
20.9 (18.1)
19.1 (16.4)
18.4 (15.9)
Gain = 32
22.5 (19.8)
21.9 (19.1)
20.5 (17.7)
20.4 (17.6)
18.4 (15.7)
18.1 (15.4)
Gain = 64
21.8 (19.5)
20.9 (18.4)
19.9 (17.1)
19.7 (17)
17.8 (15.2)
17.3 (14.7)
Gain = 128
21 (18.6)
20.2 (17.6)
19.1 (16.3)
18.9 (16.1)
17 (14.3)
16.5 (13.7)
Fast Settling Filter (Sinc3 + Sinc1)
Table 15. RMS Noise (Peak-to-Peak Noise) vs. Gain and Output Data Rate (µV), Full Power Mode (Average by 16)
Filter Word
(Dec.)
384
120
24
20
2
1
Output Data Rate
(SPS)
2.78
8.89
44.44
53.33
533.33
1066.67
Gain = 1
0.22 (1.4)
0.31 (2.1)
0.7 (4.8)
0.77 (5.2)
6.1 (46)
44 (320)
Gain = 2
0.13 (0.75)
0.21 (1.3)
0.46 (3.1)
0.5 (3.4)
3.2 (23)
22 (160)
Gain = 4
0.081 (0.44)
0.13 (0.89)
0.29 (2.1)
0.31 (2.3)
1.8 (12)
11 (80)
Gain = 8
0.048 (0.3)
0.1 (0.63)
0.22 (1.5)
0.24 (1.6)
1.1 (7.5)
5.7 (40)
Gain = 16
0.039 (0.24)
0.068 (0.47)
0.14 (0.95)
0.17 (1)
0.65 (4.3)
2.9 (22)
Gain = 32
0.026 (0.18)
0.047 (0.28)
0.098 (0.67)
0.11 (0.73)
0.4 (2.7)
1.5 (11)
Gain = 64
0.025 (0.13)
0.036 (0.25)
0.079 (0.56)
0.09 (0.66)
0.31 (2.2)
0.83 (6.2)
Gain = 128
0.019 (0.11)
0.033 (0.17)
0.071 (0.44)
0.077 (0.48)
0.27 (2)
0.54 (4)
Table 16. Effective Resolution (Peak-to-Peak Resolution) vs. Gain and Output Data Rate (Bits), Full Power Mode (Average by 16)
Filter Word
(Dec.)
384
120
24
20
2
1
Output Data Rate
(SPS)
2.78
8.89
44.44
53.33
533.33
1066.67
Gain = 1
24 (21.8)
24 (21.2)
22.8 (20)
22.6 (19.9)
19.7 (16.8)
16.8 (13.9)
Gain = 2
24 (21.7)
23.5 (20.9)
22.4 (19.6)
22.3 (19.5)
19.6 (16.8)
16.8 (13.9)
Gain = 4
23.9 (21.4)
23.2 (20.4)
22.1 (19.2)
22 (19.1)
19.4 (16.6)
16.8 (13.9)
Gain = 8
23.6 (21)
22.6 (19.9)
21.4 (18.7)
21.3 (18.6)
19.1 (16.3)
16.7 (13.9)
Rev. A | Page 29 of 90
Gain = 16
22.9 (20.3)
22.1 (19.4)
21.1 (18.3)
20.8 (18.2)
18.9 (16.1)
16.7 (13.8)
Gain = 32
22.5 (19.8)
21.7 (19.1)
20.6 (17.8)
20.4 (17.7)
18.6 (15.8)
16.6 (13.8)
Gain = 64
21.6 (19.2)
21 (18.3)
19.9 (17.1)
19.7 (16.9)
17.9 (15.1)
16.5 (13.6)
Gain = 128
21 (18.4)
20.2 (17.8)
19.1 (16.5)
19 (16.3)
17.2 (14.3)
16.1 (13.3)
AD7124-4
Data Sheet
MID POWER MODE
Sinc4
Table 17. RMS Noise (Peak-to-Peak Noise) vs. Gain and Output Data Rate (µV), Mid Power Mode
Filter
Word
(Dec.)
2047
1920
960
480
240
120
96
80
60
30
15
8
4
2
1
Output
Data
Rate
(SPS)
2.34
2.5
5
10
20
40
50
60
80
160
320
600
1200
2400
4800
Output Data
Rate (Zero
Latency
Mode) (SPS)
0.586
0.625
1.25
2.5
5
10
12.5
15
20
40
80
150
300
600
1200
f3dB
(Hz)
0.078
0.575
1.15
2.3
4.6
9.2
11.5
13.8
18.4
36.8
73.6
138
276
552
1104
Gain = 1
0.22 (1.4)
0.25 (1.4)
0.34 (2)
0.44 (2.8)
0.67 (3.8)
0.98 (6)
1 (7.4)
1.1 (7.2)
1.3 (8.4)
1.8 (11)
2.6 (17)
3.7 (23)
5.3 (36)
9.3 (72)
71 (500)
Gain = 2
0.14 (0.88)
0.17 (0.88)
0.21 (1.2)
0.28 (1.8)
0.4 (2.4)
0.58 (3.6)
0.67 (4.2)
0.7 (4.3)
0.8 (5.1)
1.2 (7.6)
1.7 (11)
2.3 (15)
3.6 (24)
6.8 (53)
37 (270)
Gain = 4
0.095 (0.6)
0.11 (0.6)
0.13 (0.77)
0.19 (1.1)
0.27 (1.6)
0.37 (2.3)
0.41 (2.5)
0.44 (3)
0.53 (3.4)
0.73 (4.6)
1 (6.6)
1.5 (9.6)
2.4 (16)
4.8 (35)
21 (160)
Gain = 8
0.062 (0.38)
0.073 (0.38)
0.085 (0.52)
0.1 (0.82)
0.2 (1.1)
0.27 (1.7)
0.28 (1.9)
0.33 (2.1)
0.37 (2.4)
0.54 (3.4)
0.79 (4.7)
1.2 (7.2)
1.9 (13)
4.1 (34)
13 (98)
Gain = 16
0.048 (0.24)
0.048 (0.24)
0.064 (0.36)
0.1 (0.55)
0.14 (0.85)
0.2 (1.1)
0.23 (1.3)
0.24 (1.4)
0.27 (1.6)
0.39 (2.4)
0.58 (3.4)
0.84 (5)
1.3 (8.2)
2.5 (19)
7.2 (55)
Gain = 32
0.036 (0.17)
0.037 (0.19)
0.052(0.25)
0.072 (0.41)
0.098 (0.64)
0.14 (0.87)
0.15 (0.95)
0.17 (1.1)
0.2 (1.3)
0.28 (1.9)
0.4 (2.5)
0.56 (4)
0.85 (6)
1.7 (13)
4.3 (33)
Gain = 64
0.024 (0.14)
0.024 (0.14)
0.04 (0.21)
0.057 (0.34)
0.081 (0.47)
0.11 (0.74)
0.13 (0.78)
0.14 (0.89)
0.18 (1.1)
0.23 (1.4)
0.33 (2)
0.46 (2.8)
0.68 (4.3)
1.3 (10)
3.1 (24)
Gain = 128
0.02 (0.1)
0.021 (0.1)
0.035 (0.2)
0.048 (0.28)
0.07 (0.43)
0.09 (0.57)
0.11 (0.7)
0.12 (0.75)
0.13 (0.82)
0.19 (1.2)
0.26 (1.5)
0.4 (2.6)
0.6 (4.5)
1.2 (9.7)
2.6 (21)
Table 18. Effective Resolution (Peak-to-Peak Resolution) vs. Gain and Output Data Rate (Bits), Mid Power Mode
Filter
Word
(Dec.)
2047
1920
960
480
240
120
96
80
60
30
15
8
4
2
1
Output
Data
Rate
(SPS)
2.34
2.5
5
10
20
40
50
60
80
160
320
600
1200
2400
4800
Output Data
Rate (Zero
Latency Mode)
(SPS)
0.586
0.625
1.25
2.5
5
10
12.5
15
20
40
80
150
300
600
1200
Gain = 1
24 (21.8)
24 (21.8)
23.8 (21.2)
23.4 (20.8)
22.8 (20.3)
22.3 (19.7)
22.2 (19.5)
22.1 (19.4)
21.9 (19.2)
21.4 (18.8)
20.9 (18.2)
20.4 (17.7)
19.8 (17.1)
19 (16.1)
16.1 (13.3)
Gain = 2
24 (21.4)
23.8 (21.4)
23.5 (21)
23.1 (20.4)
22.5 (20)
22 (19.4)
21.8 (19.2)
21.7 (19.1)
21.5 (18.9)
21 (18.9)
20.5 (17.8)
20 (17.3)
19.4 (16.7)
18.5 (15.5)
16 (13.2)
Gain = 4
23.6 (21)
23.5 (21)
23.2 (20.6)
22.7 (20.1)
22.1 (19.6)
21.7 (19)
21.5 (18.9)
21.4 (18.7)
21.1 (18.5)
20.7 (18.5)
20.2 (17.5)
19.7 (17)
19 (16.3)
18 (15.1)
15.9 (12.9)
Gain = 8
23.3 (20.6)
23 (20.6)
22.8 (20.2)
22.2 (19.6)
21.6 (19.1)
21.1 (18.5)
21 (18.3)
20.9 (18.2)
20.7 (18)
20.2 (17.5)
19.6 (17)
19 (16.4)
18.3 (15.6)
17.2 (14.2)
15.5 (12.6)
Rev. A | Page 30 of 90
Gain = 16
22.6 (20.3)
22.6 (20.3)
22.2 (19.7)
21.5 (19.1)
21.1 (18.5)
20.6 (18.1)
20.4 (17.9)
20.3 (17.8)
20.1 (17.6)
19.6 (17)
19 (16.5)
18.5 (15.9)
17.9 (15.2)
16.9 (14)
15.4 (12.5)
Gain = 32
22.1 (19.7)
22 (19.7)
21.5 (19.2)
21 (18.5)
20.6 (17.9)
20.1 (17.5)
19.9 (17.3)
19.8 (17.2)
19.6 (16.9)
19.1 (16.3)
18.6 (15.9)
18.1 (15.3)
17.5 (14.7)
16.5 (13.6)
15.1 (12.2)
Gain = 64
21.6 (19.1)
21.6 (19.1)
20.9 (18.5)
20.4 (17.8)
19.9 (17.3)
19.4 (16.8)
19.2 (16.6)
19.1 (16.4)
18.9 (16.2)
18.4 (15.8)
17.9 (15.3)
17.4 (14.8)
16.8 (14)
15.8 (12.9)
14.6 (11.7)
Gain = 128
20.9 (18.5)
20.8 (18.5)
20.1 (17.6)
19.6 (17.1)
19.1 (16.5)
18.7 (16)
18.5 (15.8)
18.4 (15.7)
18.2 (15.5)
17.7 (15)
17.2 (14.6)
16.6 (13.9)
16 (13.1)
15 (12)
13.9 (10.9)
Data Sheet
AD7124-4
Sinc3
Table 19. RMS Noise (Peak-to-Peak Noise) vs. Gain and Output Data Rate (µV), Mid Power Mode
Filter
Word
(Dec.)
2047
960
480
320
160
96
80
40
20
10
5
3
2
1
Output
Data
Rate
(SPS)
2.34
5
10
15
30
50
60
120
240
480
960
1600
2400
4800
Output
Data Rate
(Zero
Latency
Mode) (SPS)
0.78
1.67
3.33
5
10
16.67
20
40
80
160
320
533.33
800
1600
f3dB
(Hz)
0.64
1.36
2.72
4.08
8.16
13.6
16.32
32.64
65.28
130.6
261.1
435.2
652.8
1306
Gain = 1
0.25 (1.5)
0.35 (2.2)
0.5 (3.1)
0.6 (3.8)
0.83 (5.6)
1.1 (7.5)
1.2 (7.7)
1.7 (11)
2.5 (16)
3.5 (24)
6.7 (53)
25 (170)
110 (740)
880 (5800)
Gain = 2
0.17 (1)
0.23 (1.3)
0.31 (1.9)
0.38 (2.4)
0.54 (3.3)
0.72 (4.4)
0.8 (4.8)
1.1 (7)
1.6 (9.7)
2.2 (15)
4.1 (34)
13 (90)
54 (360)
430 (3100)
Gain = 4
0.087 (0.58)
0.14 (0.82)
0.19 (1.3)
0.24 (1.6)
0.34 (2.2)
0.44 (2.9)
0.48 (3.1)
0.7 (4.6)
0.94 (6.2)
1.4 (9.3)
2.5 (19)
7.1 (53)
27 (200)
220 (1500)
Gain = 8
0.065 (0.4)
0.1 (0.58)
0.14 (0.89)
0.17 (1.1)
0.24 (1.6)
0.31 (2)
0.35 (2.2)
0.47 (3.2)
0.7 (5)
1 (7)
1.8 (14)
4.2 (30)
14 (110)
110 (760)
Gain = 16
0.049 (0.27)
0.074 (0.43)
0.1 (0.63)
0.13 (0.8)
0.18 (1.1)
0.24 (1.5)
0.25 (1.6)
0.36 (2.2)
0.53 (3.2)
0.78 (5.3)
1.2 (8.7)
2.4 (18)
7.4 (51)
55 (400)
Gain = 32
0.034 (0.19)
0.053 (0.31)
0.075 (0.44)
0.089 (0.54)
0.13 (0.77)
0.17 (1)
0.18 (1.1)
0.26 (1.7)
0.37 (2.3)
0.56 (3.9)
0.84 (6.4)
1.5 (11)
3.9 (29)
27 (180)
Gain = 64
0.03 (0.16)
0.041 (0.22)
0.6 (0.35)
0.076 (0.46)
0.1 (0.65)
0.14 (0.82)
0.15 (0.94)
0.21 (1.5)
0.31 (2.1)
0.46 (3.1)
0.67 (5)
1.1 (7.8)
2.3 (16)
14 (110)
Gain = 128
0.022 (0.11)
0.034 (0.17)
0.049 (0.28)
0.062 (0.35)
0.088 (0.53)
0.11 (0.7)
0.12 (0.77)
0.18 (1.1)
0.26 (1.8)
0.38 (2.5)
0.57 (3.9)
0.89 (6.8)
1.6 (12)
7.5 (56)
Table 20. Effective Resolution (Peak-to-Peak Resolution) vs. Gain and Output Data Rate (Bits), Mid Power Mode
Filter
Word
(Dec.)
2047
960
480
320
160
96
80
40
20
10
5
3
2
1
Output
Data
Rate
(SPS)
2.34
5
10
15
30
50
60
120
240
480
960
1600
2400
4800
Output Data
Rate (Zero
Latency
Mode) (SPS)
0.78
1.67
3.33
5
10
16.67
20
40
80
160
320
533.33
800
1600
Gain = 1
24 (21.7)
23.8 (21.1)
23.3 (20.6)
23 (20.3)
22.5 (19.8)
22.1 (19.4)
22 (19.3)
21.5 (18.8)
21 (18.3)
20.4 (17.7)
19.5 (16.5)
17.6 (14.8)
15.5 (12.7)
12.5 (9.7)
Gain = 2
23.8 (21.2)
23.4 (20.8)
22.9 (20.3)
22.6 (20)
22.1 (19.5)
21.7 (19.1)
21.6 (19)
21.1 (18.5)
20.6 (18)
20.1 (17.3)
19.2 (16.2)
17.5 (14.8)
15.5 (12.7)
12.5 (9.7)
Gain = 4
23.6 (21)
23.1 (20.5)
22.6 (19.9)
22.3 (19.6)
21.8 (19.1)
21.4 (18.7)
21.3 (18.6)
20.8 (18.1)
20.3 (17.6)
19.8 (17)
19 (16)
17.4 (14.5)
15.5 (12.6)
12.5 (9.7)
Gain = 8
23.2 (20.6)
22.6 (20)
22.1 (19.4)
21.8 (19.1)
21.3 (18.6)
20.9 (18.2)
20.8 (18.1)
20.3 (17.6)
19.8 (17)
19.2 (16.4)
18.4 (15.4)
17.2 (14.3)
15.4 (12.6)
12.5 (9.7)
Gain = 16
22.6 (20.1)
22 (19.5)
21.5 (18.9)
21.2 (18.6)
20.7 (18.1)
20.3 (17.7)
20.2 (17.6)
19.7 (17.1)
19.2 (16.6)
18.6 (15.9)
18 (15.1)
17 (14.1)
15.4 (12.6)
12.5 (9.6)
Gain = 32
22.1 (19.6)
21.5 19)
21 (18.4)
20.7 (18.1)
20.2 (17.6)
19.8 (17.2)
19.7 (17.1)
19.2 (16.5)
18.7 (16)
18.1 (15.3)
17.5 (14.6)
16.7 (13.8)
15.3 (12.4)
12.5 (9.6)
Gain = 64
21.3 (18.9)
20.8 (18.4)
20.3 (17.8)
20 (17.4)
19.5 (16.9)
19.1 (16.5)
19.1 (16.3)
18.5 (15.7)
18 (15.2)
17.4 (14.6)
16.8 (13.9)
16.1 (13.3)
15 (12.3)
12.4 (9.5)
Gain = 128
20.7 (18.4)
20.1 (17.8)
19.6 (17.1)
19.3 (16.8)
18.8 (16.2)
18.4 (15.8)
18.3 (15.6)
17.7 (15.1)
17.2 (14.4)
16.7 (13.9)
16.1 (13.3)
15.4 (12.6)
14.6 (11.7)
12.4 (9.4)
Post Filters
Table 21. RMS Noise (Peak-to-Peak Noise) vs. Gain and Output Data Rate (µV), Mid Power Mode
Output Data Rate (SPS)
16.67
20
25
27.27
Gain = 1
1.1 (6.3)
1.1 (6.9)
1.2 (8)
1.3 (9.2)
Gain = 2
0.69 (4)
0.7 (4)
0.8 (4.6)
0.82 (4.8)
Gain = 4
0.41 (2.5)
0.41 (2.5)
0.46 (2.8)
0.48 (2.8)
Gain = 8
0.31 (2)
0.33 (2.1)
0.36 (2.3)
0.36 (2.3)
Gain = 16
0.23 (1.4)
0.23 (1.5)
0.25 (1.5)
0.28 (1.6)
Gain = 32
0.17 (0.96)
0.18 (0.96)
0.17 (1)
0.19 (1.1)
Gain = 64
0.13 (0.79)
0.14 (0.81)
0.15 (0.9)
0.16 (1)
Gain = 128
0.11 (0.61)
0.12 (0.67)
0.12 (0.74)
0.13 (0.79)
Table 22. Effective Resolution (Peak-to-Peak Resolution) vs. Gain and Output Data Rate (Bits), Mid Power Mode
Output Data Rate (SPS)
16.67
20
25
27.27
Gain = 1
22.1 (19.6)
22.1 (19.5)
22 (19.2)
21.9 (19)
Gain = 2
21.8 (19.2)
21.8 (19.2)
21.6 (19.1)
21.5 (19)
Gain = 4
21.5 (18.9)
21.5 (18.9)
21.4 (18.8)
21.3 (18.8)
Gain = 8
20.9 (18.3)
20.9 (18.2)
20.7 (18.1)
20.7 (18.1)
Rev. A | Page 31 of 90
Gain = 16
20.4 (17.8)
20.4 (17.7)
20.3 (17.6)
21.1 (17.6)
Gain = 32
19.8 (17.3)
19.8 (17.3)
19.7 (17.2)
19.7 (17.1)
Gain = 64
19.2 (16.6)
19 (16.6)
18.9 (16.4)
18.9 (16.3)
Gain = 128
18.4 (16)
18.3 (15.8)
18.2 (15.7)
18.2 (15.6)
AD7124-4
Data Sheet
Fast Settling Filter (Sinc4 + Sinc1)
Table 23. RMS Noise (Peak-to-Peak Noise) vs. Gain and Output Data Rate (µV), Mid Power Mode (Average by 16)
Filter Word
(Dec.)
96
30
6
5
2
1
Output Data Rate
(SPS)
2.63
8.42
42.11
50.53
126.32
252.63
Gain = 1
0.36 (2.4)
0.67 (4.2)
1.5 (9)
1.6 (9.3)
2.5 (15)
5.2 (21)
Gain = 2
0.23 (1.5)
0.44 (2.7)
0.96 (6.1)
1 (7.7)
1.6 (11)
3.1 (19)
Gain = 4
0.15 (0.82)
0.26 (1.6)
0.57 (3.7)
0.62 (4)
1 (7.2)
1.8 (11)
Gain = 8
0.1 (0.71)
0.18 (1.1)
0.42 (2.6)
0.46 (3)
0.76 (4.9)
1.4 (9.8)
Gain = 16
0.078 (0.44)
0.14 (0.8)
0.32 (1.9)
0.33 (2)
0.57 (3.7)
0.92 (6.2)
Gain = 32
0.056 (0.35)
0.1 (0.54)
0.22 (1.5)
0.24 (1.6)
0.41 (2.7)
0.62 (4.2)
Gain = 64
0.045 (0.26)
0.08 (0.48)
0.18 (1.1)
0.2 (1.3)
0.32 (2.4)
0.49 (3)
Gain = 128
0.038 (0.21)
0.067 (0.41)
0.15 (0.95)
0.17 (1.2)
0.29 (1.9)
0.41 (3)
Table 24. Effective Resolution (Peak-to-Peak Resolution) vs. Gain and Output Data Rate (Bits), Mid Power Mode (Average by 16)
Filter Word
(Dec.)
96
30
6
5
2
1
Output Data Rate
(SPS)
2.63
8.42
42.11
50.53
126.32
252.63
Gain = 1
23.7 (21)
22.8 (20.2)
21.7 (19.1)
21.5 (19)
20.9 (18.3)
19.9 (17.3)
Gain = 2
23.4 (20.7)
22.4 (19.8)
21.3 (18.6)
21.2 (18.4)
20.5 (17.8)
19.6 (17)
Gain = 4
23 (20.5)
22.2 (19.5)
21.1 (18.4)
20.9 (18.2)
20.2 (17.4)
19.4 (16.8)
Gain = 8
22.5 (19.8)
21.7 (19.1)
20.5 (17.9)
20.4 (17.8)
19.6 (17)
18.8 (16)
Gain = 16
21.9 (19.4)
21 (18.6)
19.9 (17.3)
19.8 (17.2)
19.1 (16.4)
18.4 (15.6)
Gain = 32
21.4 (18.8)
20.6 (18.1)
19.4 (16.7)
19.3 (16.6)
18.6 (15.8)
17.9 (15.2)
Gain = 64
20.7 (18.2)
19.9 (17.3)
18.7 (16)
18.5 (15.9)
17.9 (15.2)
17.3 (14.7)
Gain = 128
20 (17.5)
19.1 (16.5)
18 (15.2)
17.8 (15)
17.1 (14.3)
16.5 (13.7)
Fast Settling Filter (Sinc3 + Sinc1)
Table 25. RMS Noise (Peak-to-Peak Noise) vs. Gain and Output Data Rate (µV), Mid Power Mode (Average by 16)
Filter Word
(Dec.)
96
30
6
5
2
1
Output Data Rate
(SPS)
2.78
8.89
44.44
53.33
133.33
266.67
Gain = 1
0.39 (2.4)
0.71 (4.2)
1.5 (9.5)
1.6 (11)
6 (37)
44 (320)
Gain = 2
0.25 (1.5)
0.43 (2.5)
0.93 (6)
1 (6.9)
3.2 (20)
23 (160)
Gain = 4
0.16 (1)
0.27 (1.6)
0.59 (3.8)
0.66 (4.2)
1.8 (11)
12 (83)
Gain = 8
0.11 (0.67)
0.19 (1.1)
0.43 (2.6)
0.46 (2.8)
1 (7.2)
5.7 (41)
Gain = 16
0.08 (0.48)
0.15 (1)
0.32 (2.1)
0.35 (2.3)
0.63 (4.5)
3 (20)
Gain = 32
0.058 (0.31)
0.098 (0.64)
0.22 (1.5)
0.24 (1.6)
0.31 (3)
1.6 (9.9)
Gain = 64
0.047 (0.27)
0.083 (0.47)
0.18 (1.1)
0.2 (1.2)
0.33 (2.2)
0.84 (6.4)
Gain = 128
0.039 (0.23)
0.068 (0.4)
0.15 (0.98)
0.17 (1.1)
0.27 (1.8)
0.56 (3.5)
Table 26. Effective Resolution (Peak-to-Peak Resolution) vs. Gain and Output Data Rate (Bits), Mid Power Mode (Average by 16)
Filter
Word
(Dec.)
96
30
6
5
2
1
Output Data
Rate (SPS)
2.78
8.89
44.44
53.33
133.33
266.67
Gain = 1
23.6 (21)
22.7 (20.2)
21.7 (19)
21.5 (18.8)
19.7 (17)
16.8 (13.9)
Gain = 2
23.3 (20.7)
22.5 (19.9)
21.4 (18.7)
21.2 (18.5)
19.6 (16.9)
16.7 (13.9)
Gain = 4
22.9 (20.3)
22.2 (19.6)
21 (18.3)
20.9 (18.2)
19.4 (16.8)
16.7 (13.9)
Gain = 8
22.5 (19.8)
21.7 (19.1)
20.5 (17.9)
20.4 (17.8)
19.2 (16.4)
16.7 (13.9)
Rev. A | Page 32 of 90
Gain = 16
21.9 (19.3)
21 (18.3)
19.9 (17.2)
19.8 (17.1)
18.9 (16.1)
16.7 (13.9)
Gain = 32
21.4 (18.9)
20.6 (17.9)
19.4 (16.7)
19.3 (16.6)
18.5 (15.7)
16.6 (13.9)
Gain = 64
20.7 (18.1)
19.8 (17.3)
18.7 (16.1)
18.6 (16)
17.8 (15.1)
16.5 (13.6)
Gain = 128
19.9 (17.4)
19.1 (16.6)
18 (15.3)
17.8 (15.1)
17.1 (14.4)
16.1 (13.4)
Data Sheet
AD7124-4
LOW POWER MODE
Sinc4
Table 27. RMS Noise (Peak-to-Peak Noise) vs. Gain and Output Data Rate (µV), Low Power Mode
Filter
Word
(Dec.)
2047
1920
960
480
240
120
60
48
40
30
15
8
4
2
1
Output
Data
Rate
(SPS)
1.17
1.25
2.5
5
10
20
40
50
60
80
160
300
600
1200
2400
Output
Data
Rate
(Zero
Latency
Mode)
(SPS)
0.293
0.3125
0.625
1.25
2.5
5
10
12.5
15
20
40
75
150
300
600
f3dB
(Hz)
0.269
0.288
0.575
1.15
2.3
4.6
9.2
11.5
13.8
18.4
36.8
69
138
276
552
Gain = 1
0.22 (1.2)
0.24 (1.5)
0.37 (2.1)
0.5 (3)
0.65 (4.1)
0.9 (5.8)
1.3 (8)
1.4 (9.3)
1.6 (10)
1.8 (12)
2.6 (17)
3.7 (24)
5.2 (35)
9.4 (57)
72 (470)
Gain = 2
0.15 (0.89)
0.15 (0.89)
0.23 (1.2)
0.3 (1.7)
0.42 (2.5)
0.61 (3.5)
0.82 (5)
0.95 (6)
0.99 (6.6)
1.2 (7.5)
1.8 (11)
2.5 (17)
4 (24)
7.6 (47)
39 (240)
Gain = 4
0.095 (0.67)
0.095 (0.67)
0.13 (0.82)
0.18 (1.2)
0.26 (1.9)
0.38 (2.5)
0.53 (3.7)
0.6 (4.2)
0.64 (4.5)
0.77 (5.1)
1.1 (7.2)
1.6 (11)
2.6 (17)
5.8 (36)
22 (130)
Gain = 8
0.071 (0.41)
0.071 (0.41)
0.1 (0.61)
0.13 (0.77)
0.2 (1.1)
0.28 (1.7)
0.38 (2.4)
0.46 (2.8)
0.47 (3.2)
0.55 (3.7)
0.85 (5.7)
1.2 (7.5)
2.1 (13)
4.9 (32)
16 (110)
Gain = 16
0.053 (0.26)
0.053 (0.26)
0.068 (0.37)
0.099 (0.56)
0.14 (0.8)
0.2 1.2)
0.29 (1.8)
0.32 (2.1)
0.35 (2.2)
0.4 (2.7)
0.56 (3.9)
0.87 (5.6)
1.4 (8.5)
3 (19)
8 (49)
Gain = 32
0.043 (0.2)
0.043 (0.2)
0.055 (0.26)
0.078 (0.39)
0.1 (0.6)
0.15 (0.85)
0.21 (1)
0.24 (1.5)
0.26 (1.7)
0.3 (2)
0.41 (2.5)
0.58 (3.9)
1 (6)
1.9 (11)
4.8 (29)
Gain = 64
0.035 (0.16)
0.035 (0.16)
0.041 (0.23)
0.06 (0.31)
0.085 (0.5)
0.12 (0.68)
0.17 (0.95)
0.2 (1.1)
0.21 (1.3)
0.25 (1.6)
0.33 (2.1)
0.48 (2.9)
0.76 (5.2)
1.4 (9)
3.3 (21)
Gain = 128
0.024 (0.12)
0.024 (0.12)
0.035 (0.17)
0.052 (0.26)
0.072 (0.43)
0.096 (0.6)
0.14 (0.9)
0.16 (1)
0.17 (1.1)
0.19 (1.3)
0.28 (1.6)
0.39 (2.6)
0.6 (3.9)
1.3 (7.8)
2.6 (18)
Table 28. Effective Resolution (Peak-to-Peak Resolution) vs. Gain and Output Data Rate, Low Power Mode
Filter
Word
(Dec.)
2047
1920
960
480
240
120
60
48
40
30
15
8
4
2
1
Output
Data
Rate
(SPS)
1.17
1.25
2.5
5
10
20
40
50
60
80
160
300
600
1200
2400
Output Data
Rate (Zero
Latency
Mode) (SPS)
0.29311
0.3125
0.625
1.25
2.5
5
10
12.5
15
20
40
75
150
300
600
Gain = 1
24 (21.7)
24 (21.7)
23.7 (21.2)
23.3 (20.7)
22.9 (20.2)
22.4 (19.7)
21.9 (19.2)
21.7 (19)
21.6 (18.9)
21.4 (18.7)
20.9 (18.2)
20.4 (17.7)
19.9 (17.1)
19 (16.4)
16.1 (13.4)
Gain = 2
23.8 (21.4)
23.8 (21.3)
23.4 (21)
23 (20.5)
22.5 (19.9)
22 (19.4)
21.5 (18.9)
21.3 (18.7)
21.2 (18.5)
21 (18.3)
20.4 (17.8)
19.9 (17.2)
19.3 (16.7)
18.3 (15.7)
16 (13.4)
Gain = 4
23.7 (20.9)
23.6 (20.8)
23.2 (20.5)
22.7 (20)
22.2 (19.4)
21.7 (18.9)
21.2 (18.4)
21 (18.2)
20.9 (18.1)
20.6 (17.9)
20.1 (17.4)
19.6 (16.8)
18.9 (16.2)
17.7 (15.1)
15.8 (13.3)
Gain = 8
23.2 (20.5)
23.1 (20.5)
22.6 (20)
22.1 (19.6)
21.6 (19.1)
21.1 (18.5)
20.6 (18)
20.4 (17.8)
20.3 (17.6)
20.1 (17.4)
19.5 (16.8)
19 (16.3)
18.2 (15.6)
17 (14.3)
15.3 (12.5)
Rev. A | Page 33 of 90
Gain = 16
22.7 (20.2)
22.6 (20.1)
22.1 (19.7)
21.6 (19.1)
21.1 (18.6)
20.6 (18)
20.1 (17.4)
19.9 (17.2)
19.8 (17.1)
19.6 (16.8)
19.1 (16.3)
18.5 (15.8)
17.8 (15.2)
16.7 (14)
15.2 (12.5)
Gain = 32
21.8 (19.7)
21.8 (19.6)
21.4 (19.2)
20.9 (18.6)
20.5 (18)
20 (17.5)
19.5 (16.9)
19.3 (16.7)
19.2 (16.5)
19 (16.2)
18.5 (15.7)
18 (15.3)
17.3 (14.7)
16.3 (13.8)
15 (12.4)
Gain = 64
21.3 (18.9)
21.2 (18.9)
20.8 (18.4)
20.3 (17.9)
19.8 (17.2)
19.3 (16.8)
18.8 (16.3)
18.6 (16.1)
18.5 (15.9)
18.3 (15.6)
17.8 (15.2)
17.3 (14.7)
16.7 (13.9)
15.7 (13.1)
14.5 (11.9)
Gain = 128
20.6 (18.3)
20.6 (18.3)
20.1 (17.8)
19.5 (17.2
19.1 (16.5)
18.6 (16)
18.1 (15.4)
17.9 (15.2)
17.8 (15.1)
17.6 (14.9)
17.1 (14.5)
16.6 (13.9)
16 (13.3)
14.9 (12.3)
13.9 (11)
AD7124-4
Data Sheet
Sinc3
Table 29. RMS Noise (Peak-to-Peak Noise) vs. Gain and Output Data Rate (µV), Low Power Mode
Filter
Word
(Dec.)
2047
480
240
160
80
48
40
20
10
5
3
2
1
Output
Data
Rate
(SPS)
1.17
5
10
15
30
50
60
120
240
480
800
1200
2400
Output
Data
Rate
(Zero
Latency
Mode)
(SPS)
0.39
1.67
3.33
5
10
16.67
20
40
80
160
266.67
400
800
f3dB
(Hz)
0.32
1.36
2.72
4.08
8.16
13.6
16.32
32.64
65.28
130.6
217.6
326.4
652.8
Gain = 1
0.26 (1.5)
0.51 (3.1)
0.75 (4.5)
0.88 (5.5)
1.3 (7.8)
2.7 (9.9)
1.8 (12)
2.5 (17)
3.5 (25)
6.8 (48)
25 (180)
110 (740)
870 (5600)
Gain = 2
0.17 (0.9)
0.31 (1.9)
0.45 (2.8)
0.55 (3.3)
0.77 (4.9)
1 (6.4)
1.1 (7)
1.6 (10)
2.4 (16)
4.3 (32)
13 (98)
55 (390)
430 (2900)
Gain = 4
0.099 (0.6)
0.2 (1.3)
0.29 (2)
0.3 (2.4)
0.47 (3.3)
0.63 (4.6)
0.71 (5)
0.9 (6.1)7
1.5 (9.9)
2.6 (19)
7.4 (53)
28 (180)
220 (1400)
Gain = 8
0.072 (0.36)
0.15 (0.86)
0.21 (1.3)
0.26 (1.6)
0.36 (2.2)
0.47 (3.1)
0.52 (3.4)
0.73 (5)
1.1 (7.6)
2 (15)
4.5 (34)
15 (100)
110 (670)
Gain = 16
0.055 (0.27)
0.11 (0.65)
0.16 (0.9)
0.19 (1.2)
0.27 (1.7)
0.36 (2.2)
0.39 (2.5)
0.55 (3.7)
0.8 (5.3)
1.3 (9)
2.7 (18)
7.6 (57)
56 (370)
Gain = 32
0.039 (0.21)
0.078 (0.45)
0.11 (0.65)
0.14 (0.79)
0.19 (1.2)
0.26 (1.7)
0.27 (1.8)
0.41 (2.5)
0.56 (3.5)
0.9 (6.5)
1.6 (11)
4 (32)
28 (180)
Gain = 64
0.032 (0.16)
0.063 (0.37)
0.085 (0.51)
0.1 (0.62)
0.15 (0.94)
0.2 ( 1.3)
0.21 (1.4)
0.3 (1.9)
0.45 (2.8)
0.7 (4.5)
1.1 (7.7)
2.4 (16)
14 (100)
Gain = 128
0.026 (0.13)
0.05 (0.28)
0.071 (0.39)
0.089 (0.53)
0.12 (0.72)
0.16 (1)
0.18 (1.3)
0.26 (1.6)
0.37 (2.3)
0.55 (3.3)
0.91 (6)
1.6 (12)
7.6 (52)
Gain = 64
21.2 (18.9)
20.2 (17.7)
19.8 (17.2)
19.5 (16.9)
19 (16.3)
18.6 (15.9)
18.5 (15.8)
18 (15.3)
17.4 (14.8)
16.8 (14.1)
16.1 (13.3)
15 (12.2)
12.5 (9.6)
Gain = 128
20.5 (18.2)
19.6 (17.1)
19.1 (16.6)
18.8 (16.2)
18.3 (15.7)
17.9 (15.2)
17.7 (15.1)
17.2 (14.6)
16.7 (14.1)
16.1 (13.5)
15.4 (12.7)
14.5 (11.6)
12.3 (9.6)
Table 30. Effective Resolution (Peak-to-Peak Resolution) vs. Gain and Output Data Rate, Low Power Mode
Filter
Word
(Dec.)
2047
480
240
160
80
48
40
20
10
5
3
2
1
Output
Data Rate
(SPS)
1.17
5
10
15
30
50
60
120
120
480
800
1200
2400
Output
Data Rate
(Zero
Latency
Mode)
(SPS)
0.39
1.67
3.33
5
10
16.67
20
40
80
160
266.67
400
800
Gain = 1
24 (21.7)
23.2 (20.6)
22.7 (20.1)
22.4 (19.8)
21.9 (19.3)
21.5 (18.9)
21.4 (18.7)
20.9 (18.2)
20.4 (17.6)
19.5 (16.7)
17.6 (14.8)
15.5 (12.7)
12.5 (9.8)
Gain = 2
23.8 (21.4)
22.9 (20.3)
22.4 (19.8)
22.1 (19.5)
21.6 (19)
21.2 (18.6)
21.1 (18.4)
20.6 (17.9)
20 (17.2)
19.2 (16.3)
17.5 (14.6)
15.5 (12.7)
12.5 (9.8)
Gain = 4
23.6 (21)
22.6 (19.9)
22.1 (19.3)
21.8 (19)
21.3 (18.5)
20.9 (18.1)
20.8 (17.9)
20.3 (17.4)
19.7 (16.9)
18.8 (16)
17.4 (14.5)
15.4 (12.7)
12.5 (9.8)
Gain = 8
23 (20.7)
22 (19.5)
21.5 (18.9)
21.2 (18.6)
20.7 (18.1)
20.3 (17.6)
20.2 (17.5)
19.7 (16.9)
19.1 (16.3)
18.2 (15.4)
17.1 (14.2)
15.4 (12.6)
12.5 (9.8
Gain = 16
22.4 (20.1)
21.4 (18.9)
20.9 (18.4)
20.6 (18)
20.1 (17.5)
19.7 (17.1)
19.6 (16.9)
19.1 (16.4)
18.6 (15.9)
17.9 (15.1)
16.8 (14.1)
15.3 (12.4)
12.5 (9.7)
Gain = 32
21.9 (19.5)
20.9 (18.4)
20.4 (17.9)
20.1 (17.6)
19.6 (17)
19.2 (16.5)
19.1 (16.4)
18.6 (15.9)
18.1 (15.4)
17.4 (14.6)
16.6 (13.8)
15.2 (12.3)
12.5 (9.7)
Post Filters
Table 31. RMS Noise (Peak-to-Peak Noise) vs. Gain and Output Data Rate (µV), Low Power Mode
Output Data Rate (SPS)
16.67
20
25
27.27
Gain = 1
1.7 (12)
1.7 (11)
1.8 (11)
1.9 (11)
Gain = 2
0.96 (5.8)
1.1 (6.4)
1.1 (6.7)
1.1 (7.3)
Gain = 4
0.65 (4)
0.65 (4.2)
0.68 (4.2)
0.69 (4.4)
Gain = 8
0.45 (2.6)
0.46 (2.6)
0.52 (2.7)
0.54 (2.9)
Gain = 16
0.34 (1.9)
0.36 (1.9)
0.37 (2)
0.4 (2.1)
Gain = 32
0.25 (1.5)
0.26 (1.5)
0.26 (1.6)
0.27 (1.8)
Gain = 64
0.2 (1.2)
0.21 (1.2)
0.22 (1.2)
0.23 (1.4)
Gain = 128
0.16 (0.92)
0.17 (0.93)
0.17 (1.1)
0.18 (1.3)
Table 32. Effective Resolution (Peak-to-Peak Resolution) vs. Gain and Output Data Rate (Bits), Low Power Mode
Output Data Rate (SPS)
16.67
20
25
27.27
Gain = 1
21.5 (18.8)
21.5 (18.8)
21.4 (18.8)
21.3 (18.7)
Gain = 2
21.3 (18.7)
21.2 (18.6)
21.2 (18.5)
21.1 (18.4)
Gain = 4
20.9 (18.2)
20.9 (18.2)
20.8 (18.2)
20.8 (18.1)
Gain = 8
21.4 (17.9)
20.4 (17.9)
20.2 (17.8)
20.2 (17.7)
Rev. A | Page 34 of 90
Gain = 16
19.8 (17.3)
19.7 (17.3)
19.7 (17.3)
19.6 (17.2)
Gain = 32
19.3 (16.7)
19.2 (16.7)
19.2 (16.6)
19.1 (16.4)
Gain = 64
18.6 (16.1)
18.6 (16.1)
18.5 (15.9)
18.4 (15.8)
Gain = 128
17.9 (15.4)
17.8 (15.4)
17.8 (15.1)
17.7 (14.9)
Data Sheet
AD7124-4
Fast Settling Filter (Sinc4 + Sinc1)
Table 33. RMS Noise (Peak-to-Peak Noise) vs. Gain and Output Data Rate (µV), Low Power Mode (Average by 8)
Filter Word
(Dec.)
96
30
6
5
2
1
Output Data
Rate (SPS)
2.27
7.27
36.36
43.64
109.1
218.18
Gain = 1
0.53 (3.4)
0.89 (5.4)
2.1 (12)
2.2 (13)
3.7 (25)
8.4 (52)
Gain = 2
0.34 (2.2)
0.6 (3.6)
1.4 (8.3)
1.4 (9.7)
2.5 (18)
5.4 (34)
Gain = 4
0.19 (1.2)
0.36 (2.2)
0.82 (5.6)
0.93 (6.5)
1.5 (10)
3.3 (21)
Gain = 8
0.16 (0.97)
0.27 (1.8)
0.64 (3.9)
0.71 (4.2)
1.3 (7.5)
2.6 (16)
Gain = 16
0.1 (0.61)
0.21 (1.2)
0.43 (2.7)
0.5 (3.1)
0.86 (5.6)
1.6 (9.8)
Gain = 32
0.082 (0.48)
0.15 (0.93)
0.33 (2.1)
0.35 (2.4)
0.59 (3.5)
0.97 (6.1)
Gain = 64
0.065 (0.38)
0.12 (0.65)
0.25 (1.6)
0.28 (1.7)
0.47 (3.2)
0.75 (5.4)
Gain = 128
0.058 (0.37)
0.093 (0.59)
0.21 (1.4)
0.23 (1.5)
0.39 (2.4)
0.63 (4.7)
Table 34. Effective Resolution (Peak-to-Peak Resolution) vs. Gain and Output Data Rate (Bits), Low Power Mode (Average by 8)
Filter Word
(Dec.)
96
30
6
5
2
1
Output Data
Rate (SPS)
2.27
7.27
36.36
43.64
109.1
218.18
Gain = 1
23.2 (20.5)
22.4 (19.8)
21.2 (18.6)
21.1 (18.5)
20.4 (17.6)
19.2 (16.6)
Gain = 2
22.8 (20.1)
22 (19.4)
20.8 (18.1)
20.7 (18)
19.9 (17.1)
18.8 (16.2)
Gain = 4
22.7 (20)
21.7 (19.1)
20.5 (17.8)
20.4 (17.6)
19.6 (16.9)
18.5 (15.9)
Gain = 8
21.9 (19.3)
21.1 (18.4)
19.9 (17.3)
19.8 (17.2)
18.9 (16.3)
17.9 (15.2)
Gain = 16
21.5 (19)
20.5 (18)
19.5 (16.8)
19.3 (16.6)
18.5 (15.8)
17.6 (15)
Gain = 32
20.9 (18.3)
20 (17.4)
18.9 (16.2)
18.8 (16)
18 (15.4)
17.3 (14.7)
Gain = 64
20.2 (17.6)
19.4 (16.9)
18.3 (15.6)
18.1 (15.5)
17.3 (14.6)
16.7 (13.8)
Gain = 128
19.4 (16.7)
18.7 (16)
17.5 (14.8)
17.4 (14.7)
16.6 (14)
15.9 (13)
Fast Settling Filter (Sinc3 + Sinc1)
Table 35. RMS Noise (Peak-to-Peak Noise) vs. Gain and Output Data Rate (µV), Low Power Mode (Average by 8)
Filter Word
(Dec.)
96
30
6
5
2
1
Output Data
Rate (SPS)
2.5
8
40
48
120
240
Gain = 1
0.53 (3.6)
0.92 (5.4)
2.1 (13)
2.3 (14)
11 (72)
88 (530)
Gain = 2
0.33 (2.1)
0.58 (3.4)
1.3 (8.3)
1.5 (8.6)
5.9 (39)
45 (250)
Gain = 4
0.21 (1.4)
0.4 (2.3)
0.83 (6)
0.87 (6.6)
3.2 (23)
22 (140)
Gain = 8
0.15 (0.93)
0.28 (1.6)
0.61 (4.1)
0.7 (4.4)
1.9 (15)
11 (82)
Gain = 16
0.11 (0.6)
0.2 (1.1)
0.44 (3)
0.5 (3.3)
1.1 (8.5)
5.8 (40)
Gain = 32
0.073 (0.44)
0.14 (0.79)
0.33 (2.1)
0.36 (2.3)
0.7 (4.7)
3 (22)
Gain = 64
0.064 (0.39)
0.11 (0.62)
0.26 (1.6)
0.3 (1.7)
0.5 (3.3)
01.6 (11)
Gain = 128
0.051 (0.29)
0.094 (0.51)
0.21 (1.3)
0.23 (1.4)
0.4 (2.4)
0.94 (6.3)
Table 36. Effective Resolution (Peak-to-Peak Resolution) vs. Gain and Output Data Rate (Bits), Low Power Mode (Average by 8)
Filter Word
(Dec.)
96
30
6
5
2
1
Output Data
Rate (SPS)
2.5
8
40
48
120
240
Gain = 1
23.2 (20.4)
22.4 (19.8)
21.2 (18.6)
21 (18.4)
18.7 (16.1)
15.8 (13.2)
Gain = 2
22.8 (20.2)
22 (19.5)
20.9 (18.2)
20.7 (18.1)
18.7 (16)
15.8 (13.2)
Gain = 4
22.5 (19.8)
21.6 (19)
20.5 (17.7)
20.4 (17.5)
18.6 (15.8)
15.8 (13.2)
Gain = 8
22 (19.4)
21.1 (18.6)
20 (17.2)
19.8 (17)
18.3 (15.3)
15.7 (12.9)
Rev. A | Page 35 of 90
Gain = 16
21.4 (19)
20.6 (18.1)
19.4 (16.7)
19.3 (16.5)
18.1 (15.2)
15.7 (12.9)
Gain = 32
21 (18.4)
20.1 (17.6)
18.9 (16.2)
18.7 (16.1)
17.8 (15)
15.7 (12.8)
Gain = 64
20.2 (17.6)
19.4 (16.9)
18.2 (15.6)
18 (15.5)
17.3 (14.6)
15.6 (12.8)
Gain = 128
19.6 (17)
18.7 (16.2)
17.5 (14.9)
17.4 (14.8)
16.6 (14)
15.3 (12.6)
AD7124-4
Data Sheet
GETTING STARTED
AVDD
IN+
OUT–
VBIAS
OUT+
AIN0
AIN1
AIN2
AIN3
AIN4
AIN5
REFIN2(+) X-MUX
REFIN2(–)
IN–
OUT+
IN–
RREF
REFERENCE
DETECT
AVDD
Σ-Δ
ADC
PGA
VDD
REFIN1(–)
PSW
SERIAL
INTERFACE
AND
CONTROL
LOGIC
CHANNEL
SEQUENCER
TEMP
SENSOR
AVSS
DIGITAL
FILTER
DIAGNOSTICS
DOUT/RDY
DIN
SCLK
CS
IOVDD
INTERNAL
CLOCK
CLK
SYNC
AD7124-4
AVSS
REGCAPA
REGCAPD
NOTES
1. SIMPLIFIED BLOCK DIAGRAM SHOWN.
AVSS
DGND
13197-068
OUT–
AVDD
REFIN1(+)
IN+
Figure 65. Basic Connection Diagram
OVERVIEW
Programmable Gain Array (PGA)
The AD7124-4 is a low power ADC that incorporates a Σ-Δ
modulator, buffer, reference, gain stage, and on-chip digital
filtering, which is intended for the measurement of wide
dynamic ranges, low frequency signals (such as those in pressure
transducers), weigh scales, and temperature measurement
applications.
The analog input signal can be amplified using the PGA. The
PGA allows gains of 1, 2, 4, 8, 16, 32, 64, and 128.
Power Modes
The AD7124-4 offers three power modes: high power mode,
mid power mode, and low power mode. This allows the user
total flexibility in terms of speed, rms noise, and current
consumption.
Analog Inputs
The device can have four differential or seven pseudo differential
analog inputs. The analog inputs can be buffered or unbuffered.
The AD7124-4 uses flexible multiplexing; thus, any analog
input pin can be selected as a positive input (AINP) and any
analog input pin can be selected as a negative input (AINM).
Multiplexer
The on-chip multiplexer increases the channel count of the device.
Because the multiplexer is included on chip, any channel
changes are synchronized with the conversion process.
Reference
The device contains a 2.5 V reference, which has a drift of
15 ppm/°C maximum.
Burnout Currents
Two burnout currents, which can be programmed to 500 nA,
2 µA, or 4 µA, are included on chip to detect the presence of the
external sensor.
Σ-Δ ADC and Filter
The AD7124-4 contains a fourth-order Σ-Δ modulator followed
by a digital filter. The device has the following filter options:
•
•
•
•
•
Sinc4
Sinc3
Fast filter
Post filter
Zero latency
Channel Sequencer
The AD7124-4 allows up to 16 configurations, or channels.
These channels can consist of analog inputs, reference inputs, or
power supplies such that diagnostic functions, such as power
supply monitoring, can be interleaved with conversions. The
sequencer automatically converts all enabled channels. When
each enabled channel is selected, the time required to generate
the conversion is equal to the settling time for the selected channel.
Per Channel Configuration
Reference buffers are also included on chip, which can be used
with the internal reference and externally applied references.
The AD7124-4 allows up to eight different setups, each setup
consisting of a gain, output data rate, filter type, and a reference
source. Each channel is then linked to a setup.
Rev. A | Page 36 of 90
Data Sheet
AD7124-4
Serial Interface
The AD7124-4 has a 3-wire or 4-wire SPI. The on-chip registers
are accessed via the serial interface.
Clock
The device has an internal 614.4 kHz clock. Use either this
clock or an external clock as the clock source for the device. The
internal clock can also be made available on a pin if a clock
source is required for external circuitry.
Temperature Sensor
The on-chip temperature sensor monitors the die temperature.
Digital Outputs
The AD7124-4 has two general-purpose digital outputs. These
can be used for driving external circuitry. For example, an
external multiplexer can be controlled by these outputs.
Calibration
Both internal calibration and system calibration are included on
chip; therefore, the user has the option of removing offset or
gain errors internal to the device only, or removing the offset or
gain errors of the complete end system.
Excitation Currents
The device contains two excitation currents which can be set
independently to 50 μA, 100 μA, 250 μA, 500 μA, 750 μA, or 1 mA.
Bias Voltage
A bias voltage generator is included on chip so that signals from
thermocouples can be biased suitably. The bias voltage is set to
AVDD/2 and can be made available on any input. It can supply
multiple channels.
Bridge Power Switch (PSW)
A low-side power switch allows the user to power down bridges
that are interfaced to the ADC.
Diagnostics
The AD7124-4 includes numerous diagnostics features such as


AVDD is referred to AVSS. AVDD powers the internal analog
regulator that supplies the ADC.
IOVDD is referred to DGND. This supply sets the interface
logic levels on the SPI interface and powers an internal
regulator for operation of the digital processing.
Single Supply Operation (AVSS = DGND)
When the AD7124-4 is powered from a single supply that is
connected to AVDD, AVSS and DGND can be shorted together
on one single ground plane. With this setup, an external level
shifting circuit is required when using truly bipolar inputs to shift
the common-mode voltage. Recommended regulators include
the ADP162, which has a low quiescent current.
Split Supply Operation (AVSS ≠ DGND)
The AD7124-4 can operate with AVSS set to a negative voltage,
allowing true bipolar inputs to be applied. This allows a truly
fully differential input signal centered around 0 V to be applied
to the AD7124-4 without the need for an external level shifting
circuit. For example, with a 3.6 V split supply, AVDD = +1.8 V
and AVSS = −1.8 V. In this use case, the AD7124-4-internally
level shifts the signals, allowing the digital output to function
between DGND (nominally 0 V) and IOVDD.
When using a split supply for AVDD and AVSS, the absolute
maximum ratings must be considered (see the Absolute
Maximum Ratings section). Ensure that IOVDD is set below
3.6 V to stay within the absolute maximum ratings for the device.
DIGITAL COMMUNICATION
The AD7124-4 has a 3-wire or 4-wire SPI interface that is
compatible with QSPI™, MICROWIRE™, and DSPs. The interface
operates in SPI Mode 3 and can be operated with CS tied low. In
SPI Mode 3, SCLK idles high, the falling edge of SCLK is the
drive edge, and the rising edge of SCLK is the sample edge. This
means that data is clocked out on the falling/drive edge and data
is clocked in on the rising/sample edge.
Reference detection
Overvoltage/undervoltage detection
CRC on SPI communications
CRC on the memory map
SPI read/write checks
DRIVE EDGE
SAMPLE EDGE
13197-069





The device has two independent power supply pins: AVDD and
IOVDD.
These diagnostics allow a high level of fault coverage in an
application.
Figure 66. SPI Mode 3, SCLK Edges
Accessing the ADC Register Map
POWER SUPPLIES
The AD7124-4 operates with an analog power supply voltage
from 2.7 V to 3.6 V in low or mid power mode and from 2.9 V
to 3.6 V in full power mode. The device accepts a digital power
supply from 1.65 V to 3.6 V.
The communications register controls access to the full register
map of the ADC. This register is an 8-bit, write only register.
On power-up or after a reset, the digital interface defaults to a
state where it expects a write to the communications register;
therefore, all communication begins by writing to the
communications register.
Rev. A | Page 37 of 90
AD7124-4
Data Sheet
The data written to the communications register determines
which register is accessed and if the next operation is a read or
write. The register address bits (Bit 5 to Bit 0) determine the
specific register to which the read or write operation applies.
8-BIT COMMAND
8 BITS, 16 BITS,
OR 24 BITS OF DATA
CMD
DATA
CS
When the read or write operation to the selected register is
complete, the interface returns to its default state, where it
expects a write operation to the communications register.
DIN
In situations where interface synchronization is lost, a write
operation of at least 64 serial clock cycles with DIN high returns
the ADC to its default state by resetting the entire device, including
the register contents. Alternatively, if CS is used with the digital
interface, returning CS high resets the digital interface to its
default state and aborts any current operation.
13197-070
SCLK
Figure 67. Writing to a Register (8-Bit Command with Register Address
Followed by Data of 8 Bits, 16 Bits, or 24 Bits; Data Length Is Dependent on
the Register Selected)
Figure 67 and Figure 68 illustrate writing to and reading from a
register by first writing the 8-bit command to the communications
register followed by the data for the addressed register.
8-BIT COMMAND
8 BITS, 16 BITS,
24 BITS, OR
32 BITS OUTPUT
CS
Reading the ID register is the recommended method for verifying
correct communication with the device. The ID register is a read
only register and contains the value 0x02 for the AD7124-4. The
communication register and ID register details are described in
Table 37 and Table 38.
CMD
DIN
DOUT/RDY
DATA
13197-071
SCLK
Figure 68. Reading from a Register (8-Bit Command with Register Address
Followed by Data of 8 Bits, 16 Bits, 24 Bits, or 32 Bits; Data Length on DOUT Is
Dependent on the Register Selected, CRC Enabled)
Table 37. Communications Register
Reg.
0x00
Name
COMMS
Bits
[7:0]
Bit 7
WEN
Bit 6
R/W
Bit 5
Bit 4
Bit 3
Bit 2
RS[5:0]
Bits
[7:0]
Bit 7
Bit 6
Bit 5
DEVICE_ID
Bit 4
Bit 3
Bit 1
Bit 0
Reset
0x00
RW
W
Bit 0
Reset
0x02
RW
R
Table 38. ID Register
Reg.
0x05
Name
ID
Rev. A | Page 38 of 90
Bit 2
Bit 1
SILICON_REVISION
Data Sheet
AD7124-4
CONFIGURATION OVERVIEW
Channel Configuration
After power-on or reset, the AD7124-4 default configuration is
as follows:
The AD7124-4 has 16 independent analog input channels and
eight independent setups. The user can select any of the analog
input pairs on any channel, as well as any of the eight setups for
any channel, giving the user full flexibility in the channel configuration. This also allows per channel configuration when using all
differential inputs because each channel can have its own
dedicated setup.
•
•
•
Channel: Channel 0 is enabled, AIN0 is selected as the
positive input, and AIN1 is selected as the negative input.
Setup 0 is selected.
Setup: the input and reference buffers are disabled, the gain
is set to 1, and the external reference is selected.
ADC control: the AD7124-4 is in low power mode,
continuous conversion mode and the internal oscillator is
enabled and selected as the master clock source.
Diagnostics: the only diagnostic enabled is the
SPI_IGNORE_ERR function.
Note that only a few of the register setting options are shown;
this list is just an example. For full register information, see the
On-Chip Registers section.
Figure 69 shows an overview of the suggested flow for changing
the ADC configuration, divided into the following three blocks:
•
•
•
•
Channel configuration (see Box A in Figure 69)
Setup (see Box B in Figure 69)
Diagnostics (see Box C in Figure 69)
ADC control (see Box D in Figure 69)
Along with the analog inputs, signals such as the power supply
or reference can also be used as inputs; they are routed to the
multiplexer internally when selected. The AD7124-4 allows the
user to define 16 configurations, or channels, to the ADC. This
allows diagnostics to be interleaved with conversions.
Channel Registers
Use the channel registers to select which input pins are either the
positive analog input or the negative analog input for that
channel. This register also contains a channel enable/disable bit
and the setup selection bits, which are used to select which of
the eight available setups to use for this channel.
When the AD7124-4 is operating with more than one channel
enabled, the channel sequencer cycles through the enabled
channels in sequential order, from Channel 0 to Channel 15. If a
channel is disabled, it is skipped by the sequencer. Details of the
channel register for Channel 0 are shown in Table 39.
A
CHANNEL CONFIGURATION
SELECT POSITIVE AND NEGATIVE INPUT FOR EACH ADC CHANNEL
SELECT ONE OF 8 SETUPS FOR ADC CHANNEL
B
SETUP
8 POSSIBLE ADC SETUPS
SELECT FILTER, OUTPUT DATA RATE, GAIN AND MORE
C
DIAGNOSTICS
ENABLE CRC, SPI READ AND WRITE CHECKS
ENABLE LDO CHECKS, AND MORE
D
ADC CONTROL
SELECT ADC OPERATING MODE, CLOCK SOURCE,
SELECT POWER MODE, DATA + STATUS, AND MORE
13197-072
•
Figure 69. Suggested ADC Configuration Flow
Table 39. Channel 0 Register
Reg. Name
Bits Bit 7
0x09 CHANNEL_0 [15:8] Enable
[7:0]
Bit 6
Bit 5
Setup
Bit 4
Bit 3
Bit 2
0
AINP[2:0]
AINM[4:0]
Rev. A | Page 39 of 90
Bit 1
Bit 0
AINP[4:3]
Reset RW
0x8001 RW
AD7124-4
Data Sheet
ADC Setups
bipolar mode, the ADC accepts negative differential input voltages,
and the output coding is offset binary. In unipolar mode, the ADC
accepts only positive differential voltages, and the coding is straight
binary. In either case, the input voltage must be within the AVDD
and AVSS supply voltages. The user can also select the reference
source using these registers. Four options are available: an
internal 2.5 V reference, an external reference connected
between REFIN1(+) and REFIN1(−), an external reference
connected between REFIN2(+) and REFIN2(−), or AVDD to AVSS.
The PGA gain is also set; gains of 1, 2, 4, 8, 16, 32, 64, and 128
are provided. The analog input buffers and reference input
buffers for the setup can also be enabled using this register.
The AD7124-4 has eight independent setups. Each setup
consists of the following four registers:
•
•
•
•
Configuration register
Filter register
Offset register
Gain register
For example, Setup 0 consists of Configuration Register 0, Filter
Register 0, Offset Register 0, and Gain Register 0. Figure 70
shows the grouping of these registers. The setup is selectable
from the channel registers detailed in the Channel Configuration
section. This allows each channel to be assigned to one of eight
separate setups. Table 40 through Table 43 show the four
registers that are associated with Setup 0. This structure is
repeated for Setup 1 to Setup 7.
Filter Registers
The filter registers select which digital filter is used at the output
of the ADC modulator. The filter type and the output data rate
are selected by setting the bits in this register. For more information,
see the Digital Filter section.
Configuration Registers
The configuration registers allow the user to select the output
coding of the ADC by selecting between bipolar and unipolar. In
CONFIGURATION
REGISTERS
FILTER
REGISTERS
GAIN
REGISTERS
OFFSET
REGISTERS
CONFIG_0
0x19
FILTER_0 0x21
GAIN_0
0x31
OFFSET_0 0x29
CONFIG_1
0x1A
FILTER_1 0x22
GAIN_1
0x32
OFFSET_1 0x2A
CONFIG_2
0x1B
FILTER_2 0x23
GAIN_2
0x33
OFFSET_2 0x2B
CONFIG_3
0x1C
FILTER_3 0x24
GAIN_3
0x34
OFFSET_3 0x2C
CONFIG_4
0x1D
FILTER_4 0x25
GAIN_4
0x35
OFFSET_4 0x2D
CONFIG_5
0x1E
FILTER_5 0x26
GAIN_5
0x36
OFFSET_5 0x2E
CONFIG_6
0x1F
FILTER_6 0x27
GAIN_6
0x37
OFFSET_6 0x2F
CONFIG_7
0x20
FILTER_7 0x28
GAIN_7
0x38
SELECT DIGITAL
FILTER TYPE
AND OUTPUT DATA RATE
ANALOG INPUT BUFFERS
REFERENCE BUFFERS
BURNOUT
REFERENCE SOURCE
GAIN
GAIN CORRECTION
OPTIONALLY
PROGRAMMED
PER SETUP AS REQUIRED
OFFSET_7 0x30
OFFSET CORRECTION
OPTIONALLY PROGRAMMED
PER SETUP AS REQUIRED
SINC4
SINC3
SINC4 + SINC1
SINC3 + SINC1
ENHANCED 50Hz/60Hz REJECTION
13197-073
SELECT PERIPHERAL
FUNCTIONS FOR
ADC CHANNEL
Figure 70. ADC Setup Register Grouping
Table 40. Configuration 0 Register
Reg.
0x19
Name
CONFIG_0
Bits
Bit 7
[15:8]
[7:0] REF_BUFM
Bit 6
Bit 5
Bit 4
0
AIN_BUFP
AIN_BUFM
Bit 3
Bipolar
REF_SEL
Bit 2
Bit 1
Burnout
PGA
Bit 0
REF_BUFP
Reset
0x0860
RW
RW
Table 41. Filter 0 Register
Reg.
0x28
Name
FILTER_0
Bits
Bit 7
[23:9]
[15:8]
[7:0]
Bit 6
Filter
Bit 5
Bit 4
REJ60
Bit 3
0
Bit 2
Bit 1
Bit 0
Reset
RW
POST_FILTER
SINGLE_CYCLE 0x060180 RW
FS[10:8]
FS[7:0]
Table 42. Offset 0 Register
Reg.
0x29
Name
OFFSET_0
Bits
[23:0]
Bits[23:0]
Offset[23:0]
Reset
RW
0x800000 RW
Bits[23:0]
Gain[23:0]
Reset
RW
0x5XXXXX RW
Table 43. Gain 0 Register
Reg.
0x31
Name
GAIN_0
Bits
[23:0]
Rev. A | Page 40 of 90
Data Sheet
AD7124-4
Offset Registers
When a diagnostic is enabled, the corresponding flag is contained
in the error register. All enabled flags are OR’ed to control the
ERR flag in the status register. Thus, if an error occurs (for example,
the SPI CRC check detects an error), the relevant flag (for example,
the SPI_CRC_ERR flag) in the error register is set. The ERR flag
in the status register is also set. This is useful when the status bits
are appended to conversions. The ERR bit indicates if an error has
occurred. The user can then read the error register for more
details on the error source.
The offset registers hold the offset calibration coefficient for the
ADC. The power-on reset value of an offset register is 0x800000.
The offset registers are 24-bit read/write registers. The poweron reset value is automatically overwritten if an internal or
system zero-scale calibration is initiated by the user or if the offset
registers are written to by the user.
Gain Registers
The gain registers are 24-bit registers that hold the gain
calibration coefficient for the ADC. The gain registers are
read/write registers. The gain is factory calibrated at a gain of 1;
thus, the default value varies from device to device. The default
value is automatically overwritten if an internal or system fullscale calibration is initiated by the user. For more information
on calibration, see the Calibration section.
The frequency of the on-chip oscillator can also be monitored
on the AD7124-4. The MCLK_COUNT register monitors the
master clock pulses. Table 44 to Table 46 give more detail on the
diagnostic registers. See the Diagnostics section for more detail
on the diagnostics available.
ADC Control Register
The ADC control register configures the core peripherals for use
by the AD7124-4 and the mode for the digital interface. The
power mode (full power, mid power, or low power) is selected
via this register. Also, the mode of operation is selected, for example,
continuous conversion or single conversion. The user can also
select the standby and power-down modes, as well as any of the
calibration modes. In addition, this register contains the clock
source select bits and the internal reference enable bits. The
reference select bits are contained in the setup configuration
registers (see the ADC Setups section for more information).
Diagnostics
The ERROR_EN register enables and disables the numerous
diagnostics on the AD7124-4. By default, the SPI_IGNORE
function is enabled, which indicates inappropriate times to
communicate with the ADC (for example, during power-up and
during a reset). Other diagnostics include
•
•
•
•
•
SPI read and write checks, which ensure that only valid
registers are accessed
SCLK counter, which ensures that the correct number of
SCLK pulses are used
SPI CRC
Memory map CRC
LDO checks
The digital interface operation is also selected via the ADC
control register. This register allows the user to enable the data
plus status read and continuous read mode. For more details, see
the Digital Interface section. The details of this register are
shown in Table 47.
Table 44. Error Register
Reg.
0x06
Name
Error
Bits
[23:16]
Bit 7
[15:8]
AINP_OV_
ERR
ALDO_PSM_
ERR
[7:0]
Bit 6
Bit 5
Bit 4
Bit 3
LDO_CAP_ERR
Bit 2
ADC_CAL_ERR
AINM_OV_
ERR
SPI_SCLK_
CNT_ERR
AINM_UV_
ERR
SPI_READ_
ERR
REF_DET_ERR
0
SPI_WRITE_
ERR
SPI_CRC_ERR
0
AINP_UV_
ERR
SPI_IGNORE_
ERR
Bit 1
ADC_CONV_
ERR
DLDO_PSM_
ERR
MM_CRC_
ERR
Bit 0
ADC_SAT_
ERR
0
Reset
0x000000
Bit 1
ADC_CONV_
ERR_EN
DLDO_PSM_
ERR_EN
MM_CRC_
ERR_EN
Bit 0
ADC_SAT_
ERR_EN
ALDO_PSM_
TRIP_TEST_EN
0
RW
R
0
Table 45. Error Enable Register
Reg.
0x07
Name
ERROR_EN
Bits
[23:16]
Bit 7
0
[15:8]
AINP_OV_
ERR_EN
ALDO_PSM_
ERR_EN
[7:0]
Bit 6
MCLK_CNT_
EN
AINP_UV_
ERR_EN
SPI_IGNORE_
ERR_EN
Bit 5
LDO_CAP_
CHK_TEST_EN
AINM_OV_
ERR_EN
SPI_SCLK_
CNT_ERR_EN
Bit 4
Bit 3
LDO_CAP_CHK
AINM_UV_
ERR_EN
SPI_READ_
ERR_EN
REF_DET_
ERR_EN
SPI_WRITE_
ERR_EN
Bit 2
ADC_CAL_
ERR_EN
DLDO_PSM_
TRIP_TEST_EN
SPI_CRC_
ERR_EN
Reset
0x000040
RW
RW
Table 46. MCLK Count Register
Reg.
0x08
Name
MCLK_COUNT
Bits
[7:0]
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
MCLK_COUNT
Bit 2
Bit 1
Bit 0
Reset
0x00
RW
R
Table 47. ADC Control Register
Reg.
0x01
Name
ADC_CONTROL
Bits
[15:8]
Bit 7
Bit 6
0
[7:0]
POWER_MORE
Bit 5
Bit 4
DOUT_RDY_DEL
Bit 3
CONT_ READ
Mode
Rev. A | Page 41 of 90
Bit 2
DATA_STATUS
Bit 1
CS_EN
Bit 0
REF_EN
CLK_SEL
Reset
0x0000
RW
RW
AD7124-4
Data Sheet
Understanding Configuration Flexibility
In Figure 71, Figure 72, and Figure 73, the registers shown in
black font are programmed for this configuration. The registers
shown in gray font are redundant.
The most straightforward implementation of the AD7124-4 is
to use differential inputs with adjacent analog inputs and run all
of them with the same setup, gain correction, and offset correction
register. For example, the user requires four differential inputs.
In this case, the user selects the following differential inputs: AIN0/
AIN1, AIN2/AIN3, AIN4/AIN5, AIN6/AIN7.
Programming the gain and offset registers is optional for any
use case, as indicated by the dashed lines between the register
blocks. If an internal or system offset or full-scale calibration is
performed, the gain and offset registers for the selected channel
are automatically updated.
An alternative way to implement these four fully differential inputs
is by taking advantage of the eight available setups. Motivation for
this includes having a different speed, noise, or gain requirement on
some of the four differential inputs vs. other inputs, or there may be
a specific offset or gain correction for particular channels. Figure 72
shows how each of the differential inputs can use a separate setup,
allowing full flexibility in the configuration of each channel.
CHANNEL
REGISTERS
CH0 0x09
AIN1
CH1 0x0A
AIN2
CH2 0x0B
AIN3
CH3 0x0C
AIN4
CH4 0x0D
AIN5
CH5 0x0E
AIN6
CH6 0x0F
AIN7
CH7 0x10
CH8 0x11
CH9 0x12
CH10 0x13
CH11 0x14
CH12 0x15
CH13 0x16
CH14 0x17
CH15 0x18
SELECT ANALOG INPUT PARTS
ENABLE THE CHANNEL
SELECT SETUP 0
CONFIGURATION
REGISTERS
FILTER
REGISTERS
GAIN
REGISTERS
OFFSET
REGISTERS
CONFIG_0 0x19
FILTER_0 0x21
GAIN_0
0x31
OFFSET_0 0x29
CONFIG_1
0x1A
FILTER_1 0x22
GAIN_1
0x32
OFFSET_1 0x2A
CONFIG_2 0x1B
FILTER_2 0x23
GAIN_2
0x33
OFFSET_2 0x2B
CONFIG_3 0x1C
FILTER_3 0x24
GAIN_3
0x34
OFFSET_3 0x2C
CONFIG_4 0x1D
FILTER_4 0x25
GAIN_4
0x35
OFFSET_4 0x2D
CONFIG_5 0x1E
FILTER_5 0x26
GAIN_5
0x36
OFFSET_5 0x2E
CONFIG_6 0x1F
FILTER_6 0x27
GAIN_6
0x37
OFFSET_6 0x2F
CONFIG_7 0x20
FILTER_7 0x28
GAIN_7
0x38
OFFSET_7 0x30
SELECT PERIPHERAL
FUNCTIONS FOR
ADC CHANNEL
SELECT DIGITAL
FILTER TYPE
AND OUTPUT DATA RATE
ANALOG INPUT BUFFERS
REFERENCE BUFFERS
BURNOUT
REFERENCE SOURCE
GAIN
SINC4
SINC3
SINC4 + SINC1
GAIN CORRECTION
OFFSET CORRECTION
OPTIONALLY
OPTIONALLY PROGRAMMED
PROGRAMMED
PER SETUP AS REQUIRED
PER SETUP AS REQUIRED
13197-074
AIN0
SINC3 + SINC1
ENHANCED 50Hz/60Hz REJECTION
Figure 71. Four Fully Differential Inputs, All Using a Single Setup (CONFIG_0, FILTER_0, GAIN_0, OFFSET_0)
CHANNEL
REGISTERS
AIN0
CH0
AIN1
CH1 0x0A
AIN2
CH2 0x0B
AIN3
CH3 0x0C
AIN4
CH4 0x0D
AIN5
CH5 0x0E
AIN7
CH6 0x0F
CH7
0x10
CH8
0x11
CH9
0x12
CH10 0x13
CH11 0x14
CH12 0x15
CH13 0x16
CH14 0x17
CH15 0x18
SELECT ANALOG INPUT PARTS
ENABLE THE CHANNEL
SELECT SETUP
CONFIGURATION
REGISTERS
FILTER
REGISTERS
GAIN
REGISTERS
OFFSET
REGISTERS
CONFIG_0 0x19
FILTER_0 0x21
GAIN_0
0x31
OFFSET_0 0x29
CONFIG_1
0x1A
FILTER_1 0x22
GAIN_1
0x32
OFFSET_1 0x2A
CONFIG_2 0x1B
FILTER_2 0x23
GAIN_2
0x33
OFFSET_2 0x2B
CONFIG_3 0x1C
FILTER_3 0x24
GAIN_3
0x34
OFFSET_3 0x2C
CONFIG_4 0x1D
FILTER_4 0x25
GAIN_4
0x35
OFFSET_4 0x2D
CONFIG_5 0x1E
FILTER_5 0x26
GAIN_5
0x36
OFFSET_5 0x2E
CONFIG_6 0x1F
FILTER_6 0x27
GAIN_6
0x37
OFFSET_6 0x2F
CONFIG_7 0x20
FILTER_7 0x28
GAIN_7
0x38
OFFSET_7 0x30
SELECT PERIPHERAL
FUNCTIONS FOR
ADC CHANNEL
SELECT DIGITAL
FILTER TYPE
AND OUTPUT DATA RATE
ANALOG INPUT BUFFERS
REFERENCE BUFFERS
BURNOUT
REFERENCE SOURCE
GAIN
SINC4
SINC3
SINC4 + SINC1
GAIN CORRECTION
OFFSET CORRECTION
OPTIONALLY
OPTIONALLY PROGRAMMED
PROGRAMMED
PER SETUP AS REQUIRED
PER SETUP AS REQUIRED
SINC3 + SINC1
ENHANCED 50Hz/60Hz REJECTION
Figure 72. Four Fully Differential Inputs with a Separate Setup per Channel
Rev. A | Page 42 of 90
13197-075
AIN6
0x09
Data Sheet
AD7124-4
Figure 73 shows an example of how the channel registers span
between the analog input pins and the setup configurations
downstream. In this random example, two differential inputs and
two single-ended inputs are required. The single-ended inputs are
the AIN0/AIN7 and AIN6/AIN7 combinations. The first differential input pair (AIN0/AIN1) uses Setup 0. The two single-ended
input pairs (AIN0/AIN7 and AIN6/AIN7) are set up as diagnostics;
therefore, they use a separate setup (Setup 1). The final differential
input (AIN2/AIN3) also uses a separate setup: Setup 2.
Given that three setups are selected for use, the CONFIG_0,
CONFIG_1, and CONFIG_2 registers are programmed as
required, and the FILTER_0, FILTER_1, and FILTER_2 registers
are also programmed as required. Optional gain and offset
correction can be employed on a per setup basis by
programming the GAIN_0, GAIN_1, and GAIN_2 registers
and the OFFSET_0, OFFSET_1, and OFFSET_2 registers.
In the example shown in Figure 73, the CHANNEL_0 to
CHANNEL_3 registers are used. Setting the MSB (the enable
bit) in each of these registers enables the four combinations via
the crosspoint multiplexer. When the AD7124-4 converts, the
sequencer transitions in ascending sequential order from
CHANNEL_0 to CHANNEL_1 to CHANNEL_2, and then on
to CHANNEL_3 before looping back to CHANNEL_0 to repeat
the sequence.
CHANNEL
REGISTERS
CHANNEL_0 0x09
AIN1
CHANNEL_1 0x0A
AIN2
CHANNEL_2 0x0B
AIN3
CHANNEL_3 0x0C
AIN4
CHANNEL_4 0x0D
AIN5
CHANNEL_5 0x0E
AIN6
CHANNEL_6 0x0F
AIN7
CHANNEL_7 0x10
CONFIG_0
CONFIG_1
CHANNEL_9 0x12
CHANNEL_10 0x13
CHANNEL_11 0x14
CHANNEL_13 0x16
CHANNEL_14 0x17
CHANNEL_15 0x18
SELECT ANALOG INPUT PARTS
ENABLE THE CHANNEL
SELECT SETUP
OFFSET
REGISTERS
0x19
FILTER_0 0x21
GAIN_0
0x31
OFFSET_0 0x29
0x1A
FILTER_1 0x22
GAIN_1
0x32
OFFSET_1 0x2A
GAIN_2
0x1B
0x33
OFFSET_2 0x2B
CONFIG_3
0x1C
FILTER_3 0x24
GAIN_3
0x34
OFFSET_3 0x2C
CONFIG_4
0x1D
FILTER_4 0x25
GAIN_4
0x35
OFFSET_4 0x2D
CONFIG_5
0x1E
FILTER_5 0x26
GAIN_5
0x36
OFFSET_5 0x2E
CONFIG_6
0x1F
FILTER_6 0x27
GAIN_6
0x37
OFFSET_6 0x2F
0x20
FILTER_7 0x28
GAIN_7
0x38
OFFSET_7 0x30
CONFIG_7
SELECT DIGITAL
FILTER TYPE
AND OUTPUT DATA RATE
SELECT PERIPHERAL
FUNCTIONS FOR
ADC CHANNEL
ANALOG INPUT BUFFERS
REFERENCE BUFFERS
BURNOUT
REFERENCE SOURCE
GAIN
GAIN
REGISTERS
FILTER_2 0x23
CONFIG_2
CHANNEL_8 0x11
CHANNEL_12 0x15
FILTER
REGISTERS
CONFIGURATION
REGISTERS
SINC4
SINC3
SINC4 + SINC1
OFFSET CORRECTION
GAIN CORRECTION
OPTIONALLY
OPTIONALLY PROGRAMMED
PROGRAMMED
PER SETUP AS REQUIRED
PER SETUP AS REQUIRED
SINC3 + SINC1
ENHANCED 50Hz/60Hz REJECTION
Figure 73. Mixed Differential and Single-Ended Configuration Using Multiple Shared Setups
Rev. A | Page 43 of 90
13197-076
AIN0
AD7124-4
Data Sheet
ADC CIRCUIT INFORMATION
ANALOG INPUT CHANNEL
The channels are configured using the AINP[4:0] bits and the
AINM[4:0] bits in the channel registers (see Table 48). The device
can be configured to have four differential inputs, seven pseudo
differential inputs, or a combination of both. When using
differential inputs, use adjacent analog input pins to form the input
pair. Using adjacent pins minimizes any mismatch between the
channels.
The AD7124-4 uses flexible multiplexing; thus, any of the analog
input pins, AIN0 to AIN7, can be selected as a positive input or
a negative input. This feature allows the user to perform diagnostics
such as checking that pins are connected. It also simplifies printed
circuit board (PCB) design. For example, the same PCB can
accommodate 2-wire, 3-wire, and 4-wire resistance temperature
detectors (RTDs).
The inputs can be buffered or unbuffered at a gain of 1 but are
automatically buffered when the gain exceeds 1. The AINP and
AINM buffers are enabled/disabled separately using the AIN_BUFP
and AIN_BUFM bits in the configuration register (see Table 49). In
buffered mode, the input channel feeds into a high impedance
input stage of the buffer amplifier. Therefore, the input can tolerate
significant source impedances and is tailored for direct connection
to external resistive type sensors such as strain gages or RTDs.
AVDD
AIN0
AVSS
AVDD
AVDD
AIN1
When the device is operated in unbuffered mode, the device has
a higher analog input current. Note that this unbuffered input
path provides a dynamic load to the driving source. Therefore,
resistor/capacitor (RC) combinations on the input pins can
cause gain errors, depending on the output impedance of the
source that is driving the ADC input.
BURNOUT
CURRENTS
AVSS
PGA
TO ADC
AVDD
AIN6
The absolute input voltage in unbuffered mode (gain = 1)
includes the range between AVSS − 50 mV and AVDD + 50 mV.
The absolute input voltage range in buffered mode at a gain of 1 is
restricted to a range between AVSS + 100 mV and AVDD − 100 mV.
The common-mode voltage must not exceed these limits;
otherwise, linearity and noise performance degrade.
AVSS
AVSS
AVDD
13197-077
AIN7
AVSS
When the gain is greater than 1, the analog input buffers are
automatically enabled. The PGA placed in front of the input
buffers is rail-to-rail; thus, in this case, the absolute input voltage
includes the range from AVSS − 50 mV to AVDD + 50 mV.
Figure 74. Analog Input Multiplexer Circuit
Table 48. Channel Register
Reg.
0x09 to
0x18
Name
Bits
CHANNEL_0 to [15:8]
CHANNEL_15 [7:0]
Bit 7
Enable
Bit 6
Bit 5
Setup
Bit 4
Bit 3
Bit 2
Bit 1
0
AINP[2:0]
Bit 0
AINP[4:3]
Reset
0x8001
RW
RW
Reset
0x0860
RW
RW
AINM[4:0]
Table 49. Configuration Register
Reg.
0x19 to
0x20
Name
CONFIG_0 to
CONFIG_7
Bits
[15:8]
[7:0]
Bit 7
Bit 6
REF_BUFM
AIN_BUFP
Bit 5
0
AIN_BUFM
Bit 4
Bit 3
Bipolar
REF_SEL
Rev. A | Page 44 of 90
Bit 2
Bit 1
Burnout
Bit 0
REF_BUFP
PGA
Data Sheet
AD7124-4
PROGRAMMABLE GAIN ARRAY (PGA)
BUF
PGA1
24-BIT
Σ-Δ ADC
PGA2
BUF
13197-080
X-MUX
When the gain stage is enabled, the output from the multiplexer
is applied to the input of the PGA. The presence of the PGA means
that signals of small amplitude can be gained within the
AD7124-4 and still maintain excellent noise performance.
ANALOG
BUFFERS
Figure 75. PGA
The AD7124-4 can be programmed to have a gain of 1, 2, 4, 8,
16, 32, 64, or 128 by using the PGA bits in the configuration
register (see Table 49). The PGA consists of two stages. For a
gain of 1, both stages are bypassed. For gains of 2 to 8, a single
stage is used, whereas for gains greater than 8, both stages are used.
The analog input range is ±VREF/gain. Therefore, with an external
2.5 V reference, the unipolar ranges are from 0 mV to 19.53 mV
to 0 V to 2.5 V, and the bipolar ranges are from ±19.53 mV to
±2.5 V. For high reference values, for example, VREF = AVDD, the
analog input range must be limited. Consult the Specifications
section for more details on these limits.
REFERENCE
The AD7124-4 has an embedded 2.5 V reference. The embedded
reference is a low noise, low drift reference with 15 ppm/°C drift
maximum for the LFCSP package and 10 ppm/°C drift maximum for the TSSOP package. Including the reference on the
AD7124-4 reduces the number of external components needed
in applications such as thermocouples, leading to a reduced
PCB size.
BAND GAP
REF
AVDD
AVSS
REFIN1(+)
The common-mode range for the differential reference inputs is
from AVSS − 50 mV to AVDD + 50 mV when the reference
buffers are disabled. The reference inputs can also be buffered
on-chip. The buffers require 100 mV of headroom. The reference
voltage of REFIN (REFINx(+) − REFINx(−)) is 2.5 V nominal,
but the AD7124-4 is functional with reference voltages from
1 V to AVDD.
In applications where the excitation (voltage or current) for the
transducer on the analog input also drives the reference voltage
for the devices, the effect of the low frequency noise in the excitation source is removed, because the application is ratiometric. If
the AD7124-4 is used in nonratiometric applications, use a low
noise reference.
The recommended 2.5 V reference voltage sources for the
AD7124-4 include the ADR4525, which is a low noise, low power
reference. Note that the reference input provides a high impedance,
dynamic load when unbuffered. Because the input impedance of
each reference input is dynamic, resistor/capacitor combinations
on these inputs can cause dc gain errors if the reference inputs
are unbuffered, depending on the output impedance of the
source driving the reference inputs.
Reference voltage sources typically have low output impedances
and are, therefore, tolerant to having decoupling capacitors on
REFINx(+) without introducing gain errors in the system. Deriving
the reference input voltage across an external resistor means that
the reference input sees a significant external source impedance.
In this situation, using the reference buffers is required.
3V
4.7µF
0.1µF
ADR4525
2.5V REF
1µF
4.7µF
REFINx(+)
REFINx(–)
REFIN1(–)
AVSS
13197-082
REFOUT
available on the REFOUT pin. A 0.1 µF decoupling capacitor is
required on REFOUT when the internal reference is active.
REFIN2(+)
REFIN2(–)
Figure 77. ADR4525 to AD7124-4 Connections
BIPOLAR/UNIPOLAR CONFIGURATION
24-BIT
Σ-Δ ADC
13197-081
REFERENCE
BUFFERS
Figure 76. Reference Connections
This reference can be used to supply the ADC (by setting the
REF_EN bit in the ADC_CONTROL register to 1) or an
external reference can be applied. For external references, the
ADC has a fully differential input capability for the channel. In
addition, the user can select one of two external reference options
(REFIN1 or REFIN2). The reference source for the AD7124-4 is
selected using the REF_SEL bits in the configuration register
(see Table 49). When the internal reference is selected, it is
internally connected to the modulator. It can also be made
The analog input to the AD7124-4 can accept either unipolar or
bipolar input voltage ranges, which allows the user to tune the
ADC input range to the sensor output range. When a split
power supply is used, the device accepts truly bipolar inputs.
When a single power supply is used, a bipolar input range does
not imply that the device can tolerate negative voltages with
respect to system AVSS. Unipolar and bipolar signals on the
AINP input are referenced to the voltage on the AINM input.
For example, if AINM is 1.5 V and the ADC is configured for
unipolar mode with a gain of 1, the input voltage range on the
AINP input is 1.5 V to 3 V when VREF = AVDD = 3 V. If the ADC
is configured for bipolar mode, the analog input range on the
AINP input is 0 V to AVDD. The bipolar/unipolar option is chosen
by programming the bipolar bit in the configuration register.
Rev. A | Page 45 of 90
AD7124-4
Data Sheet
DATA OUTPUT CODING
EXCITATION CURRENTS
When the ADC is configured for unipolar operation, the output
code is natural (straight) binary with a zero differential input
voltage resulting in a code of 00 … 00, a midscale voltage resulting
in a code of 100 … 000, and a full-scale input voltage resulting
in a code of 111 … 111. The output code for any analog input
voltage can be represented as
The AD7124-4 also contains two matched, software configurable,
constant current sources that can be programmed to equal 50 µA,
100 µA, 250 µA, 500 µA, 750 µA, or 1 mA. These current sources
can be used to excite external resistive bridges or RTD sensors.
Both current sources source currents from AVDD and can be
directed to any of the analog input pins (see Figure 78).
Code = (2N × AIN × Gain)/VREF
The pins on which the currents are made available are programmed
using the IOUT1_CH and IOUT0_CH bits in the IO_CONTROL_1
register (see Table 50). The magnitude of each current source is
individually programmable using the IOUT1 and IOUT0 bits in
the IO_CONTROL_1 register. In addition, both currents can be
output to the same analog input pin.
When the ADC is configured for bipolar operation, the output
code is offset binary with a negative full-scale voltage resulting
in a code of 000 … 000, a zero differential input voltage resulting
in a code of 100 … 000, and a positive full-scale input voltage
resulting in a code of 111 … 111. The output code for any
analog input voltage can be represented as
Code = 2
N−1
Note that the on-chip reference does not need to be enabled
when using the excitation currents.
× ((AIN × Gain/VREF) + 1)
where:
N = 24.
AIN is the analog input voltage.
Gain is the gain setting (1 to 128).
IOUT0 IOUT1
VBIAS
AVDD
AIN0
AVSS
VBIAS
AVDD
AVDD
AIN1
BURNOUT
CURRENTS
AVSS
PGA
TO ADC
AVSS
VBIAS
AVDD
13197-083
AIN7
AVSS
Figure 78. Excitation Current and Bias Voltage Connections
Table 50. Input/Output Control 1 Register
Reg.
0x03
Name
IO_
CONTROL_
1
Bits
[23:16]
[15:8]
[7:0]
Bit 7
GPIO_DAT2
PDSW
Bit 6
Bit 5
GPIO_DAT1
0
0
IOUT1_CH
Bit 4
0
IOUT1
Bit 3
GPIO_CTRL2
Rev. A | Page 46 of 90
Bit 2
GPIO_CTRL1
Bit 1
0
IOUT0
IOUT0_CH
Bit 0
0
Reset
0x000000
RW
RW
Data Sheet
AD7124-4
BRIDGE POWER-DOWN SWITCH
In bridge applications such as strain gages and load cells, the
bridge itself consumes the majority of the current in the system.
For example, a 350 Ω load cell requires 8.6 mA of current when
excited with a 3 V supply. To minimize the current consumption of
the system, the bridge can be disconnected (when it is not being
used) using the bridge power-down switch. The switch can
withstand 30 mA of continuous current, and it has an on
resistance of 10 Ω maximum. The PDSW bit in the
IO_CONTROL_1 register controls the switch.
LOGIC OUTPUTS
The AD7124-4 has two general-purpose digital outputs: P1 and
P2. These are enabled using the GPIO_CTRL bits in the
IO_CONTROL_1 register (see Table 50). The pins can be
pulled high or low using the GPIO_DATx bits in the register;
that is, the value at the pin is determined by the setting of the
GPIO_DATx bits. The logic levels for these pins are determined
by AVDD rather than by IOVDD. When the IO_CONTROL_1
register is read, the GPIO_DATx bits reflect the actual value at
the pins; this is useful for short-circuit detection.
These pins can be used to drive external circuitry, for example,
an external multiplexer. If an external multiplexer is used to
increase the channel count, the multiplexer logic pins can be
controlled via the AD7124-4 general-purpose output pins. The
general-purpose output pins can be used to select the active
multiplexer pin. Because the operation of the multiplexer is
independent of the AD7124-4, reset the modulator and filter
using the SYNC pin or by writing to the mode or configuration
register each time that the multiplexer channel is changed.
BIAS VOLTAGE GENERATOR
A bias voltage generator is included on the AD7124-4 (see
Figure 78). It biases the negative terminal of the selected input
channel to (AVDD − AVSS)/2. This function is useful in thermocouple applications, as the voltage generated by the thermocouple
must be biased around some dc voltage if the ADC operates from a
single power supply. The bias voltage generator is controlled using
the VBIASx bits in the IO_CONTROL_2 register (see Table 52).
The power-up time of the bias voltage generator is dependent
on the load capacitance. Consult the Specifications section for
more details.
CLOCK
The AD7124-4 includes an internal 614.4 kHz clock on chip.
This internal clock has a tolerance of ±5%. Use either the
internal clock or an external clock as the clock source to the
AD7124-4. The clock source is selected using the CLK_SEL bits
in the ADC_CONTROL register (see Table 53).
The internal clock can also be made available at the CLK pin.
This is useful when several ADCs are used in an application and
the devices must be synchronized. The internal clock from one
device can be used as the clock source for all ADCs in the
system. Using a common clock, the devices can be synchronized
by applying a common reset to all devices, or the SYNC pin can
be pulsed.
POWER MODES
The AD7124-4 has three power modes: full power mode, mid
power mode, and low power mode. The mode is selected using
the POWER_MODE bits in the ADC_CONTROL register. The
power mode affects the power consumption of the device as
well as changing the master clock frequency. A 614.4 kHz clock
is used by the device. However, this clock is internally divided,
the division factor being dependent on the power mode. Thus,
the range of output data rates and performance is affected by
the power mode.
Table 51. Power Modes
Power
Mode
Full Power
Mid Power
Low Power
1
Master Clock
(kHz)
614.4
153.6
76.8
Output Data
Rate1 (SPS)
9.37 to 19,200
2.34 to 4800
1.17 to 2400
Current
See the
Specifications
section
Unsettled, using a sinc3/sinc4 filter.
Table 52. Input/Output Control 2 Register
Reg.
0x04
Name
IO_CONTROL_2
Bit 7
VBIAS7
0
Bit 6
VBIAS6
0
Bit 5
0
VBIAS3
Bit 4
0
VBIAS2
Bit 3
VBIAS5
Bit 2
VBIAS4
Bit 1
0
VBIAS1
Bit 0
0
VBIAS0
Reset
0x0000
RW
RW
Reset
0x0000
RW
RW
Table 53. ADC Control Register
Reg.
0x01
Name
ADC_CONTROL
Bit 7
Bit 6
0
POWER_MODE
Bit 5
Bit 4
DOUT_RDY_DEL
Bit 3
CONT_READ
Mode
Rev. A | Page 47 of 90
Bit 2
DATA_STATUS
Bit 1
CS_EN
Bit 0
REF_EN
CLK_SEL
AD7124-4
Data Sheet
STANDBY AND POWER-DOWN MODES
In standby mode, most blocks are powered down. The LDOs
remain active so that registers maintain their contents. If
enabled, the reference, internal oscillator, digital outputs P1 to
P4, the bias voltage generator, and the low-side power switch
remain active. These blocks can be disabled also, if required, by
setting the corresponding bits appropriately. The excitation
currents, reference detection, and LDO capacitor detection
functions are disabled in standby mode.
Other diagnostics remain active if enabled when the ADC is in
standby mode. Diagnostics can be enabled or disabled while in
standby mode. However, any diagnostics that require the master
clock (undervoltage/overvoltage detection, LDO trip tests,
memory map CRC, and MCLK counter) must be enabled when
the ADC is in continuous conversion mode or idle mode; these
diagnostics do not function if enabled in standby mode.
The standby current is typically 15 µA when the LDOs only are
enabled. If functions such as the bias voltage generator remain
active in standby mode, the current increases by 36 µA typically.
If the internal oscillator remains active in standby mode, the
current increases by 22 µA typically. When exiting standby
mode, the AD7124-4 requires 130 MCLK cycles to power up
and settle.
In power-down mode, all blocks are powered down, including
the LDOs. All registers lose their contents, and the digital outputs
P1 to P4 are placed in tristate. To prevent accidental entry to
power-down mode, the ADC must first be placed into standby
mode. Exiting power-down mode requires 64 SCLK cycles
with CS = 0 and DIN = 1, that is, a serial interface reset. The
AD7124-4 requires 2 ms typically to power up and settle. The
POR_FLAG in the status register can be monitored to determine
the end of the power up/settling period. After this time, the user
can access the on-chip registers. The power-down current is 2
µA typically.
DIGITAL INTERFACE
The programmable functions of the AD7124-4 are controlled
using a set of on-chip registers. Data is written to these registers
via the serial interface. Read access to the on-chip registers is
also provided by this interface. All communications with the
device must start with a write to the communications register.
After power-on or reset, the device expects a write to its
communications register. The data written to this register
determines whether the next operation is a read operation or a
write operation, and determines to which register this read or
write operation occurs. Therefore, write access to any of the
other registers on the devices begins with a write operation to
the communications register, followed by a write to the selected
register. A read operation from any other register (except when
continuous read mode is selected) starts with a write to the
communications register, followed by a read operation from the
selected register.
The serial interface of the AD7124-4 consists of four signals: CS,
DIN, SCLK, and DOUT/RDY. The DIN line transfers data into
the on-chip registers, whereas DOUT/RDY accesses data from
the on-chip registers. SCLK is the serial clock input for the
device, and all data transfers (either on DIN or DOUT/RDY)
occur with respect to the SCLK signal. The DOUT/RDY pin
also operates as a data ready signal; the line goes low when a
new data-word is available in the output register. It is reset high
when a read operation from the data register is complete. It also
goes high before the data register updates to indicate when not
to read from the device, to ensure that a data read is not attempted
while the register is being updated. CS is used to select a device.
It can decode the AD7124-4 in systems where several components
are connected to the serial bus.
Figure 3 and Figure 4 show timing diagrams for interfacing to
the AD7124-4 with CS decoding the devices. Figure 3 shows the
timing for a read operation from the output shift register of the
AD7124-4. Figure 4 shows the timing for a write operation to
the input shift register. A delay is required between consecutive
SPI communications. Figure 5 shows the delay required between
SPI read/write operations. It is possible to read the same word
from the data register several times, even though the DOUT/RDY
line returns high after the first read operation. However, care
must be taken to ensure that the read operations are complete
before the next output update occurs. In continuous read mode,
the data register can be read only once.
The serial interface can operate in 3-wire mode by tying CS low.
In this case, the SCLK, DIN, and DOUT/RDY lines communicate
with the AD7124-4. The end of the conversion can be monitored
using the RDY bit in the status register. This scheme is suitable
for interfacing to microcontrollers. If CS is required as a decoding
signal, it can be generated from a port pin. For microcontroller
interfaces, it is recommended that SCLK idle high between data
transfers.
The AD7124-4 can be operated with CS being used as a frame
synchronization signal. This scheme is useful for DSP interfaces.
In this case, the first bit (MSB) is effectively clocked out by CS,
because CS normally occurs after the falling edge of SCLK in
DSPs. SCLK can continue to run between data transfers,
provided the timing numbers are obeyed.
CS must be used to frame read and write operations and the
CS_EN bit in the ADC_CONTROL register must be set when
the diagnostics SPI_READ_ERR, SPI_WRITE_ERR, or
SPI_SCLK_CNT_ERR are enabled.
The serial interface can be reset by writing a series of 1s on the
DIN input. See the Reset section for more details. Reset returns
the interface to the state in which it is expecting a write to the
communications register
The AD7124-4 can be configured to continuously convert or
perform a single conversion (see Figure 79 through Figure 81).
Rev. A | Page 48 of 90
Data Sheet
AD7124-4
Single Conversion Mode
Continuous Conversion Mode
In single conversion mode, the AD7124-4 performs a single
conversion and is placed in standby mode after the conversion
is complete. The AD7124-4 requires 130 MCLK cycles to exit
standby mode. If a master clock is present (external master clock
or the internal oscillator is enabled), DOUT/RDY goes low to
indicate the completion of a conversion. When the data-word is
read from the data register, DOUT/RDY goes high. The data
register can be read several times, if required, even when
DOUT/RDY is high.
Continuous conversion is the default power-up mode. The
AD7124-4 converts continuously, and the RDY bit in the status
register goes low each time a conversion is complete. If CS is low,
the DOUT/RDY line also goes low when a conversion is complete.
To read a conversion, write to the communications register,
indicating that the next operation is a read of the data register.
When the data-word is read from the data register, DOUT/RDY
goes high. The user can read this register additional times, if
required. However, the user must ensure that the data register is
not being accessed at the completion of the next conversion;
otherwise the new conversion word is lost.
If several channels are enabled, the ADC automatically sequences
through the enabled channels and performs a conversion on
each channel. When a conversion is started, DOUT/RDY goes
high and remains high until a valid conversion is available and CS
is low. As soon as the conversion is available, DOUT/RDY goes low.
The ADC then selects the next channel and begins a conversion.
The user can read the present conversion while the next conversion
is being performed. As soon as the next conversion is complete,
the data register is updated; therefore, the user has a limited
period in which to read the conversion. When the ADC has
performed a single conversion on each of the selected channels,
it returns to idle mode.
If the DATA_STATUS bit in the ADC_CONTROL register is set
to 1, the contents of the status register are output along with the
conversion each time that the data read is performed. The four
LSBs of the status register indicate the channel to which the
conversion corresponds.
When several channels are enabled, the ADC automatically
sequences through the enabled channels, performing one
conversion on each channel. When all channels are converted,
the sequence starts again with the first channel. The channels
are converted in order from lowest enabled channel to highest
enabled channel. The data register is updated as soon as each
conversion is available. The DOUT/RDY pin pulses low each
time a conversion is available. The user can then read the
conversion while the ADC converts the next enabled channel.
If the DATA_STATUS bit in the ADC_CONTROL register is set
to 1, the contents of the status register, along with the conversion
data, are output each time the data register is read. The status
register indicates the channel to which the conversion corresponds.
CS
DIN
0x01
0x0004
0x42
DATA
13197-087
DOUT/RDY
SCLK
Figure 79. Single Conversion Configuration
CS
DOUT/RDY
0x42
0x42
DATA
DATA
13197-088
DIN
SCLK
Figure 80. Continuous Conversion Configuration
Rev. A | Page 49 of 90
AD7124-4
Data Sheet
CS
DIN
0x01
0x0800
DOUT/RDY
DATA
DATA
13197-089
SCLK
Figure 81. Continuous Read Configuration
Continuous Read Mode
In continuous read mode, it is not required to write to the
communications register before reading ADC data; apply the
required number of SCLKs after DOUT/RDY goes low to
indicate the end of a conversion. When the conversion is read,
DOUT/RDY returns high until the next conversion is available.
In this mode, the data can be read only once. Ensure that the dataword is read before the next conversion is complete. If the user
has not read the conversion before the completion of the next
conversion, or if insufficient serial clocks are applied to the
AD7124-4 to read the word, the serial output register is reset
when the next conversion is complete, and the new conversion
is placed in the output serial register. The ADC must be configured
for continuous conversion mode to use continuous read mode.
To enable continuous read mode, set the CONT_READ bit in
the ADC_CONTROL register. When this bit is set, the only serial
interface operations possible are reads from the data register. To
exit continuous read mode, issue a dummy read of the ADC data
register command (0x42) while RDY is low. Alternatively, apply a
software reset, that is, 64 SCLKs with CS = 0 and DIN = 1. This
resets the ADC and all register contents. These are the only
commands that the interface recognizes after it is placed in
continuous read mode. DIN must be held low in continuous
read mode until an instruction is to be written to the device.
If multiple ADC channels are enabled, each channel is output in
turn, with the status bits being appended to the data if DATA_
STATUS is set in the ADC_CONTROL register. The status
register indicates the channel to which the conversion corresponds.
DATA_STATUS
The contents of the status register can be appended to each
conversion on the AD7124-4. This is a useful function if several
channels are enabled. Each time a conversion is output, the
contents of the status register are appended. The four LSBs of
the status register indicate to which channel the conversion
corresponds. In addition, the user can determine if any errors
are being flagged via the ERROR_FLAG bit. To append the status
register contents to every conversion, the DATA_STATUS bit in
the ADC_CONTROL register is set to 1.
SERIAL INTERFACE RESET (DOUT_RDY_DEL
AND CS_EN BITS)
The instant at which the DOUT/RDY pin changes from being a
DOUT pin to a RDY pin is programmable on the AD7124-4. By
default, the D OUT/RDY pin changes functionality after a period
of time following the last SCLK rising edge, the SCLK edge on
which the LSB is read by the processor. This time is 10 ns
minimum by default and, by setting the DOUT_RDY_DEL bit
in the ADC_ CONTROL register to 1, can be extended to 110
ns minimum.
By setting the CS_EN bit in the ADC_CONTROL register to 1, the
change of functionality is controlled by the CS rising edge. In
this case, the DOUT/RDY pin continues to output the LSB of
the register being read until CS is taken high. Only on the CS
rising edge does the pin change from a DOUT pin to a RDY pin.
This configuration is useful if the CS signal is used to frame all
read operations. If CS is not used to frame all read operations,
set CS_EN to 0 so that DOUT/RDY changes functionality
following the last SCLK edge in the read operation.
CS_EN must be set to 1 and the CS signal must be used to frame all
read and write operations when the SPI_READ_ERR,
SPI_WRITE_ERR, and SPI_SCLK_CNT_ERR diagnostic
functions are enabled.
The serial interface is always reset on the CS rising edge, that is,
the interface is reset to a known state whereby it awaits a write
to the communications register. Therefore, if a read or write
operation is performed by performing multiple 8- bit data
transfers, CS must be held low until the all bits are transferred.
RESET
The circuitry and serial interface of the AD7124-4 can be reset
by writing 64 consecutive 1s to the device. This resets the logic,
the digital filter, and the analog modulator, and all on-chip
registers are reset to their default values. A reset is automatically
performed on power-up. A reset requires a time of 90 MCLK
cycles. The POR_FLAG bit in the status register is set to 1 when
the reset is initiated and then is set to 0 when the reset is
Rev. A | Page 50 of 90
Data Sheet
AD7124-4
complete. A reset is useful if the serial interface becomes
asynchronous due to noise on the SCLK line.
CALIBRATION
The AD7124-4 provides four calibration modes that can be
used to eliminate the offset and gain errors on a per setup basis:
•
•
•
•
Internal zero-scale calibration mode
Internal full-scale calibration mode
System zero-scale calibration mode
System full-scale calibration mode
Only one channel can be active during calibration. After each
conversion, the ADC conversion result is scaled using the ADC
calibration registers before being written to the data register.
The default value of the offset register is 0x800000, and the nominal
value of the gain register is 0x5XXXXX. The calibration range
of the ADC gain is from 0.4 × VREF/gain to 1.05 × VREF/gain.
The following equations show the calculations that are used in
each calibration mode. In unipolar mode, the ideal
relationship—that is, not taking into account the ADC gain
error and offset error—is as follows:
 0.75 × VIN

Data = 
× 2 23 − (Offset − 0x800000)  ×
 VREF

Gain
×2
0x400000
In bipolar mode, the ideal relationship—that is, not taking into
account the ADC gain error and offset error—is as follows:
 0.75 × VIN

Data = 
× 2 23 − (Offset − 0x800000)  ×
V
REF


Gain
+ 0x800000
0x400000
To start a calibration, write the relevant value to the mode bits
in the ADC_CONTROL register. The DOUT/RDY pin and
the RDY bit in the status register go high when the calibration
initiates. When the calibration is complete, the contents of the
corresponding offset or gain register are updated, the RDY bit
in the status register is reset, the DOUT/RDY pin returns low
(if CS is low), and the AD7124-4 reverts to idle mode.
During an internal offset calibration, the selected positive
analog input pin is disconnected, and it is connected internally
to the selected negative analog input pin. For this reason, it is
necessary to ensure that the voltage on the selected negative
analog input pin does not exceed the allowed limits and is free
from excessive noise and interference.
To perform an internal full-scale calibration, a full-scale input
voltage is automatically connected to the selected analog input
for this calibration. A full-scale calibration is recommended
each time the gain of a channel is changed to minimize the fullscale error. When performing internal calibrations, the internal
full-scale calibration must be performed before the internal
zero-scale calibration. Therefore, write the value 0x800000 to
the offset register before performing the internal full-scale
calibration, which ensures that the offset register is at its default
value.
System calibrations expect the system zero-scale (offset) and
system full-scale (gain) voltages to be applied to the ADC pins
before initiating the calibration modes. As a result, errors
external to the ADC are removed. The system zero-scale
calibration must be performed before the system full-scale
calibration.
From an operational point of view, treat a calibration like
another ADC conversion. Set the system software to monitor
the RDY bit in the status register or the DOUT/RDY pin to
determine the end of a calibration via a polling sequence or an
interrupt-driven routine.
An internal/system offset calibration and system full-scale
calibration requires a time equal to the settling time of the
selected filter to be completed. The internal full-scale
calibration requires a time equal to one settling period for a
gain of 1 and a time of four settling periods for gains greater
than 1.
A calibration can be performed at any output data rate. Using
lower output data rates results in better calibration accuracy and
is accurate for all output data rates. A new calibration is required
for a given channel if the reference source or the gain for that
channel is changed.
Offset and system full-scale calibrations can be performed in
any power mode. Internal full-scale calibrations can be performed
in the low power or mid power modes only. Thus, when using
full power mode, the user must select mid or low power mode
to perform the internal full-scale calibration. However, an internal
full-scale calibration performed in low or mid power mode is
valid in full power mode, if the same gain is used.
The offset error is typically ±15 µV for gains of 1 to 8 and
±200/gain µV for higher output data rates. An internal or system
offset calibration reduces the offset error to the order of the
noise. The gain error is factory calibrated at ambient temperature
and at a gain of 1. Following this calibration, the gain error is
±0.0025% maximum. Therefore, internal full-scale calibrations
at a gain of 1 are not supported on the AD7124-4. For other
gains, the gain error is −0.3%. An internal full-scale calibration at
ambient temperature reduces the gain error to ±0.016%
maximum for gains of 2 to 8 and ±0.025% typically for higher
gains. A system full-scale calibration reduces the gain error to the
order of the noise.
The AD7124-4 provides the user with access to the on-chip
calibration registers, allowing the microprocessor to read the
calibration coefficients of the device and to write its own
calibration coefficients from prestored values in the EEPROM.
A read or write of the offset and gain registers can be performed
at any time except during an internal or self-calibration. The
Rev. A | Page 51 of 90
AD7124-4
Data Sheet
values in the calibration registers are 24 bits wide. The span and
offset of the device can also be manipulated using the registers.
remove an offset of ±0.2 × VREF/gain, the span range that the
system calibration can handle is ±0.85 × VREF/gain.
SPAN AND OFFSET LIMITS
SYSTEM SYNCHRONIZATION
Whenever a system calibration mode is used, the amount of
offset and span which can be accommodated is limited. The
overriding requirement in determining the amount of offset
and gain which can be accommodated by the device is the
requirement that the positive full-scale calibration limit is
≤1.05 × VREF/gain. This allows the input range to go 5% above
the nominal range. The built-in headroom in the AD7124-4
analog modulator ensures that the device still operates correctly
with a positive full-scale voltage which is 5% beyond the nominal.
The SYNC input allows the user to reset the modulator and the
digital filter without affecting any of the setup conditions on the
device. This allows the user to start gathering samples of the
analog input from a known point in time, that is, the rising edge
of SYNC. Take SYNC low for at least four master clock cycles to
implement the synchronization function.
The range of input span in both the unipolar and bipolar modes
has a minimum value of 0.8 × VREF/gain and a maximum value
of 2.1 × VREF/gain. However, the span, which is the difference
between the bottom of the AD7124-4 input range and the top of
its input range, must account for the limitation on the positive
full-scale voltage. The amount of offset that can be accommodated
depends on whether the unipolar or bipolar mode is being used.
The offset must account for the limitation on the positive fullscale voltage. In unipolar mode, there is considerable flexibility in
handling negative (with respect to AINM) offsets. In both
unipolar and bipolar modes, the range of positive offsets that
can be handled by the device depends on the selected span.
Therefore, in determining the limits for system zero-scale and
full-scale calibrations, the user must ensure that the offset range
plus the span range does exceed 1.05 × VREF/gain. This is best
illustrated by looking at a few examples.
If the device is used in unipolar mode with a required span of
0.8 × VREF/gain, the offset range that the system calibration can
handle is from −1.05 × VREF/gain to +0.25 × VREF/gain. If the
device is used in unipolar mode with a required span of
VREF/gain, the offset range that the system calibration can
handle is from −1.05 × VREF/gain to +0.05 × VREF/gain. Similarly,
if the device is used in unipolar mode and required to remove
an offset of 0.2× VREF/gain, the span range that the system
calibration can handle is 0.85 × VREF/gain.
If the device is used in bipolar mode with a required span of
±0.4 × VREF/gain, then the offset range which the system
calibration can handle is from −0.65 × VREF/gain to +0.65 ×
VREF/gain. If the device is used in bipolar mode with a required
span of ±VREF/gain, the offset range the system calibration can
handle is from −0.05 × VREF/gain to +0.05 × VREF/gain.
Similarly, if the device is used in bipolar mode and required to
If multiple AD7124-4 devices are operated from a common
master clock, they can be synchronized so that their data
registers are updated simultaneously. A falling edge on
the SYNC pin resets the digital filter and the analog modulator
and places the AD7124-4 into a consistent, known state. While
the SYNC pin is low, the AD7124-4 is maintained in this state.
On the SYNC rising edge, the modulator and filter exit this reset
state and, on the next clock edge, the device starts to gather
input samples again. In a system using multiple AD7124-4
devices, a common signal to their SYNC pins synchronizes their
operation. This is normally performed after each AD7124-4 has
performed its own calibration or has calibration coefficients
loaded into its calibration registers. The conversions from the
AD7124-4 devices are then synchronized.
The device exits reset on the master clock falling edge following
the SYNC low to high transition. Therefore, when multiple
devices are being synchronized, pull the SYNC pin high on the
master clock rising edge to ensure that all devices begin
sampling on the master clock falling edge. If the SYNC pin is
not taken high in sufficient time, it is possible to have a
difference of one master clock cycle between the devices; that is,
the instant at which conversions are available differs from
device to device by a maximum of one master clock cycle.
The SYNC pin can also be used as a start conversion command.
In this mode, the rising edge of SYNC starts conversion and the
falling edge of RDY indicates when the conversion is complete.
The settling time of the filter must be allowed for each data
register update. For example, if the ADC is configured to use
the sinc4 filter and zero latency is disabled, the settling time
equals 4/fADC where fADC is the output data rate when
continuously converting on a single channel.
Rev. A | Page 52 of 90
Data Sheet
AD7124-4
DIGITAL FILTER
Table 54. Filter Registers
Reg.
0x21 to
0x28
Name
FILTER_0 to
FILTER_7
Bit 7
Bit 6
Filter
Bit 5
Bit 4
REJ60
Bit 3
0
Bit 2
Bit 1
Bit 0
POST_FILTER
SINGLE_CYCLE
FS[10:8]
Reset
0x060180
RW
RW
FS[7:0]
conversion after the channel change. Subsequent conversions on
this channel occur at 1/fADC.
CHANNEL
CONVERSIONS CH A
When the AD7124-4 is powered up, the sinc4 filter is selected by
default. This filter gives excellent noise performance over the
complete range of output data rates. It also gives the best 50 Hz/
60 Hz rejection, but it has a long settling time. In Figure 82, the
blocks shown in gray are unused.
CH A CH A
CH B CH B CH B
1/fADC
DT/fCLK
Figure 83. Sinc4 Channel Change
When conversions are performed on a single channel and a
step change occurs, the ADC does not detect the change in the
analog input. Therefore, it continues to output conversions
at the programmed output data rate. However, it is at least four
conversions later before the output data accurately reflects the
analog input. If the step change occurs while the ADC is
processing a conversion, then the ADC takes five conversions
after the step change to generate a fully settled result.
ANALOG
INPUT
FULLY
SETTLED
ADC
OUTPUT
Figure 82. Sinc4 Filter
Sinc4 Output Data Rate/Settling Time
The output data rate (the rate at which conversions are available
on a single channel when the ADC is continuously converting)
is equal to
13197-093
AVERAGING
BLOCK
13197-091
MODULATOR
POST
FILTER
SINC3 /SINC4
FILTER
CHANNEL B
NOTES
1. DT = DEAD TIME
The filter bits in the filter register select between the sinc type filter.
SINC4 FILTER
CHANNEL A
13197-092
The AD7124-4 offers a great deal of flexibility in the digital
filter. The device has several filter options. The option selected
affects the output data rate, settling time, and 50 Hz and 60 Hz
rejection. The following sections describe each filter type,
indicating the available output data rates for each filter option.
The filter response along with the settling time and 50 Hz and
60 Hz rejection is also discussed.
1/fADC
Figure 84. Asynchronous Step Change in the Analog Input
The 3 dB frequency for the sinc4 filter is equal to
fADC = fCLK/(32 × FS[10:0])
f3dB = 0.23 × fADC
where:
fADC is the output data rate.
fCLK is the master clock frequency (614.4 kHz in full power mode,
153.6 kHz in mid power mode, and 76.8 kHz in low power mode).
FS[10:0] is the decimal equivalent of the FS[10:0] bits in the
filter register. FS[10:0] can have a value from 1 to 2047.
Table 55 gives some examples of the relationship between the
values in the FS[10:0] bits and the corresponding output data
rate and settling time.
The output data rate can be programmed from
Power Mode
Full Power (fCLK =
614.4 kHz)
•
•
•
9.38 SPS to 19,200 SPS for full power mode
2.35 SPS to 4800 SPS for mid power mode
1.17 SPS to 2400 SPS for low power mode
Table 55. Examples of Output Data Rates and the
Corresponding Settling Times for the Sinc4 Filter
Mid Power (fCLK =
153.6 kHz)
The settling time for the sinc4 filter is equal to
tSETTLE = (4 × 32 × FS[10:0] + Dead time)/fCLK
where Dead time = 60 when FS[10:0] = 1 and 94 when FS[10:0] > 1.
When a channel change occurs, the modulator and filter are
reset. The settling time is allowed to generate the first
Low Power (fCLK =
76.8 kHz)
Rev. A | Page 53 of 90
FS[10:0]
1920
384
320
480
96
80
240
48
40
Output Data
Rate (SPS)
10
50
60
10
50
60
10
50
60
Settling
Time (ms)
400.15
80.15
66.82
400.61
80.61
67.28
401.22
81.22
67.89
AD7124-4
Data Sheet
Sinc4 Zero Latency
Zero latency is enabled by setting the SINGLE_CYCLE bit in
the filter register to 1. With zero latency, the conversion time
when continuously converting on a single channel approximately
equals the settling time. The benefit of this mode is that a similar
period of time elapses between all conversions irrespective of
whether the conversions occur on one channel or whether several
channels are used. When the analog input is continuously sampled
on a single channel, the output data rate equals
fADC = fCLK/(4 × 32 × FS[10:0])
When switching between channels, the AD7124-4 allows the
complete settling time to generate the first conversion after the
channel change. Therefore, the ADC automatically operates in
zero latency mode when several channels are enabled—setting
the SINGLE_CYCLE bit has no benefits.
Table 56. Examples of Output Data Rates and the
Corresponding Settling Times for the Sinc4 Filter (Zero Latency)
Low Power (fCLK =
76.8 kHz)
Settling
Time (ms)
400.15
80.15
66.82
400.61
80.61
67.28
401.22
81.22
67.89
The description in the Sinc4 Filter section is valid when
manually switching channels, for example, writing to the device
to change channels. When multiple channels are enabled, the
on-chip sequencer is automatically used; the device
automatically sequences between all enabled channels. In this
case, the first conversion takes the complete settling time as
listed in Table 55. For all subsequent conversions, the time
needed for each conversion is the settling time also, but the
dead time is reduced to 30.
Sinc4 50 Hz and 60 Hz Rejection
Figure 86 shows the frequency response of the sinc4 filter when
the output data rate is programmed to 50 SPS and zero latency
is disabled. For the same configuration but with zero latency
enabled, the filter response remains the same but the output data
rate is 12.5 SPS. The sinc4 filter provides 50 Hz (±1 Hz) rejection in
excess of 120 dB minimum, assuming a stable master clock.
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–110
–120
0
25
50
75
100
FREQUENCY (Hz)
125
150
13197-095
At low output data rates, this extra delay has little impact on the
value of the settling time. However, at high output data rates, the
delay must be considered. Table 56 summarizes the output data
rate when continuously converting on a single channel and the
settling time when switching between channels for a sample of
FS[10:0] values.
Sequencer
FILTER GAIN (dB)
where Dead time = 60 when FS[10:0] = 1 and 94 when FS[10:0] > 1.
Mid Power (fCLK =
153.6 kHz)
13197-094
Figure 85. Sinc4 Zero Latency Operation
Dead time/fCLK
FS[10:0]
1920
384
320
480
96
80
240
48
40
FULLY
SETTLED
1/fADC
When the user selects another channel, there is an extra delay in
the first conversion of
Power Mode
Full Power (fCLK =
614.4 kHz)
ANALOG
INPUT
ADC
OUTPUT
where:
fADC is the output data rate.
fCLK is the master clock frequency.
FS[10:0] is the decimal equivalent of the FS[10:0] bits in the
setup filter register.
Output Data
Rate (SPS)
2.5
12.5
15
2.5
12.5
15
2.5
12.5
15
When the analog input is constant or a channel change occurs,
valid conversions are available at a near constant output data
rate. When conversions are being performed on a single
channel and a step change occurs on the analog input, the ADC
continues to output fully settled conversions if the step change is
synchronized with the conversion process. If the step change is
asynchronous, one conversion is output from the ADC, which is
not completely settled (see Figure 85).
Figure 86. Sinc4 Filter Response (50 SPS Output Data Rate, Zero Latency
Disabled or 12.5 SPS Output Data Rate, Zero Latency Enabled)
Rev. A | Page 54 of 90
Data Sheet
AD7124-4
0
Figure 87 shows the frequency response of the sinc4 filter when
the output data rate is programmed to 60 SPS and zero latency
is disabled. For the same configuration but with zero latency
enabled, the filter response remains the same but the output
data rate is 15 SPS. The sinc4 filter provides 60 Hz (±1 Hz)
rejection of 120 dB minimum, assuming a stable master clock.
–10
–20
FILTER GAIN (dB)
–30
0
–10
–20
–50
–60
–70
–80
–90
–30
–100
–40
–120
–60
0
25
–70
100
125
150
Figure 89. Sinc4 Filter Response (50 SPS Output Data Rate, Zero Latency
Disabled or 12.5 SPS Output Data Rate, Zero Latency Enabled, REJ60 = 1)
–90
–100
SINC3 FILTER
0
30
60
90
120
150
FREQUENCY (Hz)
13197-096
–110
Figure 87. Sinc4 Filter Response (60 SPS Output Data Rate, Zero Latency
Disabled or 15 SPS Output Data Rate, Zero Latency Enabled)
When the output data rate is 10 SPS with zero latency disabled
or 2.5 SPS with zero latency enabled, simultaneous 50 Hz and
60 Hz rejection is obtained. The sinc4 filter provides 50 Hz
(±1 Hz) and 60 Hz (±1 Hz) rejection of 120 dB minimum,
assuming a stable master clock.
A sinc3 filter can be used instead of the sinc4 filter. The filter is
selected using the filter bits in the filter register. This filter has
good noise performance, moderate settling time, and moderate
50 Hz and 60 Hz (±1 Hz) rejection. In Figure 90, the blocks
shown in gray are unused.
MODULATOR
POST
FILTER
SINC3 /SINC4
FILTER
AVERAGING
BLOCK
0
Figure 90. Sinc3 Filter
–10
FILTER GAIN (dB)
75
FREQUENCY (Hz)
–80
–120
50
13197-098
–110
–50
13197-099
FILTER GAIN (dB)
–40
–20
Sinc3 Output Data Rate and Settling Time
–30
The output data rate (the rate at which conversions are available on
a single channel when the ADC is continuously converting) equals
–40
–50
fADC = fCLK/(32 × FS[10:0])
–60
–70
–80
–90
–100
0
30
60
90
FREQUENCY (Hz)
120
150
13197-097
–110
–120
Figure 88. Sinc4 Filter Response (10 SPS Output Data Rate, Zero Latency
Disabled or 2.5 SPS Output Data Rate, Zero Latency Enabled)
Simultaneous 50 Hz/60 Hz rejection can also be achieved using
the REJ60 bit in the filter register. When the sinc filter places a
notch a 50 Hz, the REJ60 bit places a first order notch at 60 Hz.
The output data rate is 50 SPS when zero latency is disabled and
12.5 SPS when zero latency is enabled. Figure 89 shows the
frequency response of the sinc4 filter. The filter provides 50 Hz ±
1 Hz and 60 Hz ± 1 Hz rejection of 82 dB minimum, assuming
a stable master clock.
where:
fADC is the output data rate.
fCLK is the master clock frequency (614.4 kHz in full power mode,
153.6 kHz in mid power mode and 76.8 kHz in low power mode).
FS[10:0] is the decimal equivalent of the FS[10:0] bits in the
filter register. FS[10:0] can have a value from 1 to 2047.
The output data rate can be programmed from
•
•
•
9.38 SPS to 19,200 SPS for full power mode
2.35 SPS to 4800 SPS for mid power mode
1.17 SPS to 2400 SPS for low power mode
The settling time for the sinc3 filter is equal to
tSETTLE = (3 × 32 × FS[10:0] + Dead time)/fCLK
where Dead time = 60 when FS[10:0] = 1 and 94 FS[10:0] >1.
The 3 dB frequency is equal to
Rev. A | Page 55 of 90
f3dB = 0.272 × fADC
AD7124-4
Data Sheet
When the analog input is continuously sampled on a single
channel, the output data rate equals
Table 57 gives some examples of FS[10:0] settings and the
corresponding output data rates and settling times.
fADC = fCLK/(3 × 32 × FS[10:0])
Power Mode
Full Power (fCLK =
614.4 kHz)
Mid Power (fCLK =
153.6 kHz)
Low Power (fCLK =
76.8 kHz)
FS[10:0]
1920
384
320
480
96
80
240
48
40
Output Data
Rate (SPS)
10
50
60
10
50
60
10
50
60
Settling
Time (ms)
300.15
60.15
50.15
300.61
60.61
50.61
301.22
61.22
51.22
When a channel change occurs, the modulator and filter are
reset. The complete settling time is allowed to generate the first
conversion after the channel change (see Figure 91). Subsequent
conversions on this channel are available at 1/fADC.
CONVERSIONS
CHANNEL A
CH A
CHANNEL B
CH B CH B
CH A
1/fADC
DT/fCLK
NOTES
1. DT = DEAD TIME
13197-100
CHANNEL
Figure 91. Sinc3 Channel Change
When conversions are performed on a single channel and a step
change occurs, the ADC does not detect the change in the
analog input. Therefore, it continues to output conversions at
the programmed output data rate. However, it is at least three
conversions later before the output data accurately reflects the
analog input. If the step change occurs while the ADC is processing
a conversion, the ADC takes four conversions after the step
change to generate a fully settled result.
ANALOG
INPUT
where:
fADC is the output data rate.
fCLK is the master clock frequency.
FS[10:0] is the decimal equivalent of the FS[10:0] bits in the
filter register.
When switching channels, there is an extra delay in the first
conversion of
Dead time/fCLK
where Dead time = 60 when FS[10:0] = 1 or 94 when FS > 1.
At low output data rates, this extra delay has little impact on the
value of the settling time. However, at high output data rates, the
delay must be considered. Table 58 summarizes the output data rate
when continuously converting on a single channel and the settling
time when switching between channels for a sample of FS[10:0].
When the user selects another channel, the AD7124-4 allows
the complete settling time to generate the first conversion after
the channel change. Therefore, the ADC automatically operates
in zero latency mode when several channels are enabled—setting
the SINGLE_CYCLE bit has no benefits.
When the analog input is constant or a channel change occurs,
valid conversions are available at a near constant output data
rate. When conversions are being performed on a single channel
and a step change occurs on the analog input, the ADC continues
to output fully settled conversions if the step change is synchronized
with the conversion process. If the step change is asynchronous,
one conversion is output from the ADC that is not completely
settled (see Figure 93).
ANALOG
INPUT
FULLY
SETTLED
ADC
OUTPUT
FULLY
SETTLED
ADC
OUTPUT
1/fADC
13197-102
Table 57. Examples of Output Data Rates and the
Corresponding Settling Times for the Sinc3 Filter
3 Zero Latency Operation
1/fADC
13197-101
Figure 93. Sinc
Figure 92. Asynchronous Step Change in the Analog Input
Sinc3 Zero Latency
Zero latency is enabled by setting the SINGLE_CYCLE bit in
the filter register to 1. With zero latency, the conversion time
when continuously converting on a single channel approximately
equals the settling time. The benefit of this mode is that a similar
period of time elapses between all conversions irrespective of
whether the conversions occur on one channel or whether
several channels are used.
Table 58. Examples of Output Data Rates and the
Corresponding Settling Times for the Sinc3 Filter (Zero Latency)
Power Mode
Full Power (fCLK =
614.4 kHz)
Mid Power (fCLK =
153.6 kHz)
Low Power (fCLK =
76.8 kHz)
Rev. A | Page 56 of 90
FS[10:0]
1920
384
320
480
96
80
240
48
40
Output Data
Rate (SPS)
3.33
16.67
20
3.33
16.67
20
3.33
16.67
20
Settling
Time (ms)
300.15
60.15
50.15
300.61
60.61
50.61
301.22
61.22
51.22
Data Sheet
AD7124-4
Sinc3 50 Hz and 60 Hz Rejection
Figure 94 shows the frequency response of the sinc3 filter when
the output data rate is programmed to 50 SPS and zero latency
is disabled. For the same configuration but with zero latency
enabled, the filter response remains the same but the output
data rate is 16.67 SPS. The sinc3 filter gives 50 Hz ± 1 Hz
rejection of 95 dB minimum for a stable master clock.
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–110
–120
0
0
30
60
–10
–30
–50
–60
–70
–80
–90
–100
0
25
50
75
100
125
150
FREQUENCY (Hz)
0
13197-103
–110
–10
–20
Figure 94. Sinc3 Filter Response (50 SPS Output Data Rate, Zero Latency
Disabled or 16.67 SPS Output Data Rate, Zero Latency Enabled)
FILTER GAIN (dB)
Figure 95 shows the frequency response of the sinc3 filter when
the output data rate is programmed to 60 SPS and zero latency
is disabled. For the same configuration but with zero latency
enabled, the filter response remains the same but the output
data rate is 20 SPS. The sinc3 filter has rejection of 95 dB
minimum at 60 Hz ± 1 Hz, assuming a stable master clock.
–30
–40
–50
–60
–70
–80
–90
–100
0
–110
–10
–120
–20
0
25
50
75
100
125
150
FREQUENCY (Hz)
–30
13197-106
FILTER GAIN (dB)
150
Simultaneous 50 Hz and 60 Hz rejection can also be achieved
using the REJ60 bit in the filter register. When the sinc filter
places a notch a 50 Hz, the REJ60 bit places a first order notch
at 60 Hz. The output data rate is 50 SPS when zero latency is
disabled and 16.67 SPS when zero latency is enabled. Figure 97
shows the frequency response of the sinc3 filter with this configuration. Assuming a stable clock, the rejection at 50 Hz and 60 Hz
(±1 Hz) is in excess of 67 dB minimum.
–40
FILTER GAIN (dB)
120
Figure 96. Sinc3 Filter Response (10 SPS Output Data Rate, Zero Latency
Disabled or 3.33 SPS Output Data Rate, Zero Latency Enabled)
–20
–120
90
FREQUENCY (Hz)
13197-105
The description in the Sinc3 Filter section is valid when manually
switching channels, for example, writing to the device to change
channels. When multiple channels are enabled, the on-chip
sequencer is automatically used; the device automatically
sequences between all enabled channels. In this case, the first
conversion takes the complete settling time as listed in Table 57.
For all subsequent conversions, the time needed for each conversion
is also the settling time, but the dead time is reduced to 30.
When the output data rate is 10 SPS with zero latency disabled
or 3.33 SPS with zero latency enabled, simultaneous 50 Hz and
60 Hz rejection is obtained. The sinc3 filter has rejection of 100 dB
minimum at 50 Hz ± 1 Hz and 60 Hz ± 1 Hz (see Figure 96).
FILTER GAIN (dB)
Sequencer
Figure 97. Sinc3 Filter Response (50 SPS Output Data Rate, Zero Latency
Disabled or 16.67 SPS Output Data Rate, Zero Latency Enabled, REJ60 = 1)
–40
–50
–60
FAST SETTLING MODE (SINC4 + SINC1 FILTER)
–70
In fast settling mode, the settling time is close to the inverse of
the first filter notch; therefore, the user can achieve 50 Hz and/or
60 Hz rejection at an output data rate close to 1/50 Hz or 1/60 Hz.
The settling time is approximately equal to 1/output data rate.
Therefore, the conversion time is near constant when converting
on a single channel or when converting on several channels.
–80
–90
–100
0
30
60
90
FREQUENCY (Hz)
120
150
13197-104
–110
–120
Figure 95. Sinc3 Filter Response (60 SPS Output Data Rate, Zero Latency
Disabled or 20 SPS Output Data Rate, Zero Latency Enabled)
Rev. A | Page 57 of 90
AD7124-4
Data Sheet
13197-107
SINC3/SINC4
FILTER
AVERAGING
BLOCK
CONVERSIONS CH A
CHANNEL B
CH A CH A CH A CH A
CH B CH B CH B CH B
1/fADC DT/fCLK
NOTES
1. DT = DEAD TIME
Figure 99. Fast Settling, Sinc4 + Sinc1 Filter
POST
FILTER
MODULATOR
CHANNEL A
CHANNEL
13197-108
Enable the fast settling mode using the filter bits in the filter
register. In fast settling mode, a sinc1 filter is included after the
sinc4 filter. The sinc1 filter averages by 16 in the full power and
mid power modes and averages by 8 in the low power mode. In
Figure 98, the blocks shown in gray are unused.
Figure 98. Fast Settling Mode, Sinc4 + Sinc1 Filter
Output Data Rate and Settling Time, Sinc4 + Sinc1 Filter
When continuously converting on a single channel, the output
data rate is
fADC = fCLK/((4 + Avg − 1) × 32 × FS[10:0])
When the device is converting on a single channel and a step
change occurs on the analog input, the ADC does not detect the
change and continues to output conversions. If the step change
is synchronized with the conversion, only fully settled results
are output from the ADC. However, if the step change is
asynchronous to the conversion process, there is one intermediate
result, which is not completely settled (see Figure 100).
ANALOG
INPUT
VALID
When another channel is selected by the user, there is an extra
delay in the first conversion. The settling time is equal to
tSETTLE = ((4 + Avg − 1) × 32 × FS[10:0] + Dead time)/fCLK
where Dead time = 94.
The 3 dB frequency is equal to
f3dB = 0.44 × fADC
Table 59 lists sample FS[10:0] settings and the corresponding
output data rates and settling times.
Table 59. Examples of Output Data Rates and the
Corresponding Settling Times (Fast Settling Mode, Sinc4 + Sinc1)
Power Mode
Full Power (fCLK =
614.4 kHz,
Average by 16)
Mid Power (fCLK =
153.6 kHz,
Average by 16)
Low Power (fCLK =
76.8 kHz,
Average by 8)
FS[10:0]
120
24
20
30
6
5
30
6
5
First
Notch
(Hz)
10
50
60
10
50
60
10
50
60
Output
Data Rate
(SPS)
8.42
42.11
50.53
8.42
42.11
50.53
7.27
36.36
43.64
Settling
Time
(ms)
118.9
23.9
19.94
119.36
24.36
20.4
138.72
28.72
24.14
When the analog input is constant or a channel change occurs,
valid conversions are available at a near constant output data rate.
ADC
OUTPUT
1/fADC
13197-109
where:
fADC is the output data rate.
fCLK is the master clock frequency (614.4 kHz in full power mode,
153.6 kHz in mid power mode, and 76.8 kHz in low power mode).
Avg is 16 for the full or mid power mode and 8 for low power
mode.
FS[10:0] is the decimal equivalent of the FS[10:0] bits in the
filter register. FS[10:0] can have a value from 1 to 2047.
4
Figure 100. Step Change on the Analog Input, Sinc + Sinc1 Filter
Sequencer
The description in the Fast Settling Mode (Sinc4 + Sinc1 Filter)
section is valid when manually switching channels, for example,
writing to the device to change channels. When multiple
channels are enabled, the on-chip sequencer is automatically
used; the device automatically sequences between all enabled
channels. In this case, the first conversion takes the complete
settling time as listed in Table 59. For all subsequent
conversions, the time needed for each conversion is also the
settling time, but the dead time is reduced to 30.
50 Hz and 60 Hz Rejection, Sinc4 + Sinc1 Filter
Figure 101 shows the frequency response when FS[10:0] is set
to 24 in the full power mode or 6 in the mid power mode or low
power mode. Table 59 lists the corresponding output data rate.
The sinc filter places the first notch at
fNOTCH = fCLK/(32 × FS[10:0])
The sinc1 filter places notches at fNOTCH/Avg (Avg equaling 16 for
the full power mode and mid power mode and equaling 8 for
the low power mode). Notches are also placed at multiples of
this frequency; therefore, when FS[10:0] is set to 6 in the full
power mode or mid power mode, a notch is placed at 800 Hz
due to the sinc filter and notches are placed at 50 Hz and
multiples of 50 Hz due to the averaging. In low power mode, a
notch is placed at 400 Hz due to the sinc filter and notches are
placed at 50 Hz and multiples of 50 Hz due to the averaging.
The notch at 50 Hz is a first-order notch; therefore, the notch is
not wide. This means that the rejection at 50 Hz exactly is good,
assuming a stable master clock. However, in a band of 50 Hz ± 1 Hz,
the rejection degrades significantly. The rejection at 50 Hz ± 0.5 Hz
is 40 dB minimum, assuming a stable clock; therefore, a good
master clock source is recommended when using fast settling mode.
Rev. A | Page 58 of 90
Data Sheet
AD7124-4
0
FAST SETTLING MODE (SINC3 + SINC1 FILTER)
–10
In fast settling mode, the settling time is close to the inverse of
the first filter notch; therefore, the user can achieve 50 Hz and/or
60 Hz rejection at an output data rate close to 1/50 Hz or 1/60 Hz.
The settling time is approximately equal to 1/output data rate.
Therefore, the conversion time is near constant when converting
on a single channel or when converting on several channels.
FILTER GAIN (dB)
–30
–40
–50
–60
–70
–80
–90
–100
0
30
60
90
120
150
FREQUENCY (Hz)
13197-110
–110
–120
Enable the fast settling mode using the filter bits in the filter
register. In fast settling mode, a sinc1 filter is included after the
sinc3 filter. The sinc1 filter averages by 16 in the full power and
mid power modes and averages by 8 in low power mode. In
Figure 104, the blocks shown in gray are unused.
Figure 101. 50 Hz Rejection
0
–30
FILTER GAIN (dB)
Figure 104. Fast Settling Mode, Sinc3 + Sinc1 Filter
When continuously converting on a single channel, the output
data rate is
–20
fADC = fCLK/((3 + Avg − 1) × 32 × FS[10:0])
–40
–50
where:
fADC is the output data rate.
fCLK is the master clock frequency (614.4 kHz in full power mode,
153.6 kHz in mid power mode, and 76.8 kHz in low power mode).
Avg is 16 in full or mid power mode and 8 in low power mode.
FS[10:0] is the decimal equivalent of the FS[10:0] bits in the
filter register. FS[10:0] can have a value from 1 to 2047.
–60
–70
–80
–90
–100
0
30
60
90
120
150
FREQUENCY (Hz)
13197-111
–110
Figure 102. 60 Hz Rejection
Simultaneous 50 Hz/60 Hz rejection is achieved when FS[10:0]
is set to 384 in full power mode or 30 in the mid power and low
power modes. Notches are placed at 10 Hz and multiples of 10 Hz,
thereby giving simultaneous 50 Hz and 60 Hz rejection. The
rejection at 50 Hz ± 0.5 Hz and 60 Hz ± 0.5 Hz is 44 dB typically.
0
–10
–20
–40
–50
tSETTLE = ((3 + Avg − 1) × 32 × FS[10:0] + Dead time)/ fCLK
where Dead time = 94.
The 3 dB frequency is equal to
f3dB = 0.44 × fNOTCH
Table 60 lists some sample FS[10:0] settings and the
corresponding output data rates and settling times.
Power Mode
Full Power (fCLK =
614.4 kHz,
Average by 16)
–60
–70
–80
–90
Mid Power (fCLK =
153.6 kHz,
Average by 16)
–100
0
30
60
90
120
FREQUENCY (Hz)
Figure 103. Simultaneous 50 Hz and 60 Hz Rejection
150
13197-112
–110
–120
When another channel is selected by the user, there is an extra
delay in the first conversion. The settling time is equal to
Table 60. Examples of Output Data Rates and the
Corresponding Settling Times (Fast Settling Mode, Sinc3 + Sinc1)
–30
FILTER GAIN (dB)
AVERAGING
BLOCK
Output Data Rate and Settling Time, Sinc3 + Sinc1 Filter
–10
–120
SINC3 /SINC4
FILTER
MODULATOR
Figure 102 shows the filter response when FS[10:0] is set to 20
in full power mode or 5 in the mid power and low power modes. In
this case, a notch is placed at 60 Hz and multiples of 60 Hz. The
rejection at 60 Hz ± 0.5 Hz is equal to 40 dB minimum.
POST
FILTER
13197-113
–20
Low Power (fCLK =
76.8 kHz,
Average by 8)
Rev. A | Page 59 of 90
FS[10:0]
120
24
20
30
6
5
30
6
5
First Notch
(Hz)
10
50
60
10
50
60
10
50
60
Output Data
Rate (SPS)
8.89
44.44
53.33
8.89
44.44
53.33
8
40
48
Settling
Time (ms)
112.65
22.65
18.9
113.11
23.11
19.36
126.22
26.22
22.06
AD7124-4
Data Sheet
When the analog input is constant or a channel change occurs,
valid conversions are available at a near constant output data rate.
CHANNEL
CHANNEL A
40 dB minimum, assuming a stable clock; therefore, a good master
clock source is recommended when using fast settling mode.
0
CHANNEL B
–10
–20
–30
NOTES
1. DT = DEAD TIME
Figure 105. Fast Settling, Sinc3 + Sinc1 Filter
When the device is converting on a single channel and a step
change occurs on the analog input, the ADC does not detect
the change and continues to output conversions. When the step
change is synchronized with the conversion, only fully settled
results are output from the ADC. However, if the step change is
asynchronous to the conversion process, one intermediate result
is not completely settled (see Figure 106).
–40
–50
–60
–70
–80
–90
–100
–110
–120
0
30
60
90
120
150
FREQUENCY (Hz)
13197-116
DT/fCLK
Figure 107. 50 Hz Rejection
ANALOG
INPUT
VALID
1/fADC
13197-115
ADC
OUTPUT
Figure 108 shows the filter response when FS[10:0] is set to 20
in full power mode or 5 in the mid power and low power modes. In
this case, a notch is placed at 60 Hz and multiples of 60 Hz. The
rejection at 60 Hz ± 0.5 Hz is equal to 40 dB minimum.
0
3
Figure 106. Step Change on the Analog Input, Sinc + Sinc1 Filter
–10
–20
Sequencer
–30
FILTER GAIN (dB)
The description in the Fast Settling Mode (Sinc3 + Sinc1 Filter)
section is valid when manually switching channels, for example,
writing to the device to change channels. When multiple
channels are enabled, the on-chip sequencer is automatically
used; the device automatically sequences between all enabled
channels. In this case, the first conversion takes the complete
settling time as listed in Table 60. For all subsequent conversions,
the time needed for each conversion is also the settling time,
but the dead time is reduced to 30.
–40
–50
–60
–70
–80
–90
–100
–110
–120
0
50 Hz and 60 Hz Rejection, Sinc3 + Sinc1 Filter
30
60
90
FREQUENCY (Hz)
Figure 107 shows the frequency response when FS[10:0] is set
to 24 in the full power mode or 6 in the mid power mode or low
power mode. Table 60 lists the corresponding output data rate.
The sinc filter places the first notch at
fNOTCH = fCLK/(32 × FS[10:0])
The averaging block places notches at fNOTCH/Avg (Avg equaling
16 for the full power mode and mid power mode and equaling 8
for the low power mode). Notches are also placed at multiples of
this frequency; therefore, when FS[10:0] is set to 6 in full power
mode or mid power mode, a notch is placed at 800 Hz due to
the sinc filter and notches are placed at 50 Hz and multiples of
50 Hz due to the averaging. In low power mode, a notch is
placed at 400 Hz due to the sinc filter and notches are placed at
50 Hz and multiples of 50 Hz due to the averaging.
120
150
13197-117
1/fADC
CH B CH B CH B CH B
FILTER GAIN (dB)
CH A CH A CH A CH A
13197-114
CONVERSIONS CH A
Figure 108. 60 Hz Rejection
Simultaneous 50 Hz/60 Hz rejection is achieved when FS[10:0]
is set to 384 in full power mode or 30 in the mid power and low
power modes. Notches are placed at 10 Hz and multiples of 10 Hz,
thereby giving simultaneous 50 Hz and 60 Hz rejection. The
rejection at 50 Hz ± 0.5 Hz and 60 Hz ± 0.5 Hz is 42 dB typically.
The notch at 50 Hz is a first-order notch; therefore, the notch is not
wide. This means that the rejection at 50 Hz exactly is good, assuming a stable master clock. However, in a band of 50 Hz ± 1 Hz, the
rejection degrades significantly. The rejection at 50 Hz ± 0.5 Hz is
Rev. A | Page 60 of 90
Data Sheet
AD7124-4
0
filters are realized by post filtering the output of the sinc3 filter.
The filter bits must be set to all 1s to enable the post filter. The post
filter option to use is selected using the POST_FILTER bits in the
filter register. In Figure 110, the blocks shown in gray are unused.
–20
FILTER GAIN (dB)
–30
–40
–50
–60
MODULATOR
–70
SINC3/SINC4
FILTER
AVERAGING
BLOCK
–80
–90
Figure 110. Post Filters
–100
30
0
60
90
120
150
FREQUENCY (Hz)
13197-118
–110
–120
POST
FILTER
13197-119
–10
Figure 109. Simultaneous 50 Hz and 60 Hz Rejection
POST FILTERS
The post filters provide rejection of 50 Hz and 60 Hz
simultaneously and allow the user to trade off settling time and
rejection. These filters can operate up to 27.27 SPS or can reject
up to 90 dB of 50 Hz ± 1 Hz and 60 Hz ± 1 Hz interference. These
Table 61 shows the output data rates with the accompanying
settling times and the rejection.
When continuously converting on a single channel, the first
conversion requires a time of tSETTLE. Subsequent conversions
occur at 1/fADC. When multiple channels are enabled (either
manually or using the sequencer), the settling time is required
to generate a valid conversion on each enabled channel.
Table 61. AD7124-4 Post Filters: Output Data Rate, Settling Time (tSETTLE), and Rejection
Output Data
Rate (SPS)
27.27
25
20
16.67
1
f3dB
(Hz)
17.28
15.12
13.38
12.66
tSETTLE, Full Power
Mode (ms)
38.498
41.831
51.831
61.831
tSETTLE, Mid Power
Mode (ms)
38.998
42.331
52.331
62.331
tSETTLE, Low Power
Mode (ms)
39.662
42.995
52.995
62.995
Stable master clock used.
Rev. A | Page 61 of 90
Simultaneous Rejection of 50 Hz ± 1 Hz
and 60 Hz ± 1 Hz (dB)1
47
62
86
92
Data Sheet
0
–10
–20
–20
–30
–30
–60
–70
–70
–80
–90
–90
0
100
200
300
400
500
600
FREQUENCY (Hz)
Figure 111. DC to 600 Hz, 27.27 SPS Output Data Rate, 36.67 ms Settling Time
–100
40
0
–10
–20
–20
–30
–30
FILTER GAIN (dB)
0
–50
–60
–70
60
65
70
FREQUENCY (Hz)
Figure 112. Zoom in 40 Hz to 70 Hz, 27.27 SPS Output Data Rate, 36.67 ms
Settling Time
–100
–10
–20
–20
–30
–30
FILTER GAIN (dB)
–10
–60
–70
500
600
–100
40
13197-122
FREQUENCY (Hz)
400
Figure 113. DC to 600 Hz, 25 SPS Output Data Rate, 40 ms Settling Time
500
600
–70
–90
300
400
–60
–80
200
300
–50
–90
100
200
–40
–80
–100
40
100
Figure 115. DC to 600 Hz, 20 SPS Output Data Rate, 50 ms Settling Time
0
–50
0
FREQUENCY (Hz)
0
–40
70
–70
–90
55
65
–60
–90
50
60
–50
–80
45
55
–40
–80
–100
40
50
Figure 114. Zoom in 40 Hz to 70 Hz, 25 SPS Output Data Rate, 40 ms Settling Time
–10
–40
45
FREQUENCY (Hz)
13197-121
FILTER GAIN (dB)
–60
–80
–100
FILTER GAIN (dB)
–50
13197-124
–50
–40
45
50
55
FREQUENCY (Hz)
60
65
70
13197-125
–40
13197-123
FILTER GAIN (dB)
0
–10
13197-120
FILTER GAIN (dB)
AD7124-4
Figure 116. Zoom in 40 Hz to 70 Hz, 20 SPS Output Data Rate, 50 ms Settling Time
Rev. A | Page 62 of 90
AD7124-4
0
0
–10
–10
–20
–20
–30
–30
FILTER GAIN (dB)
–40
–50
–60
–70
–80
–40
–50
–60
–70
–80
–90
–100
40
0
100
200
300
FREQUENCY (Hz)
400
500
600
13197-126
–90
–100
Figure 117. DC to 600 Hz,16.667 SPS Output Data Rate, 60 ms Settling Time
45
50
55
FREQUENCY (Hz)
60
65
70
13197-127
FILTER GAIN (dB)
Data Sheet
Figure 118. Zoom in 40 Hz to 70 Hz, 16.667 SPS Output Data Rate, 60 ms
Settling Time
Rev. A | Page 63 of 90
AD7124-4
Data Sheet
SUMMARY OF FILTER OPTIONS
The AD7124-4 has several filter options. The filter that is
chosen affects the output data rate, settling time, the rms noise,
the stop band attenuation, and the 50 Hz and 60 Hz rejection.
Table 62 shows some sample configurations and the
corresponding performance in terms of throughput and 50 Hz
and 60 Hz rejection.
Table 62. Filter Summary1
Filter
Sinc4
Sinc4, Zero Latency
Sinc3
Fast Settling (Sinc4 + Sinc1)
Fast Settling (Sinc3 + Sinc1)
Post Filter
1
2
Power Mode
All
All
All
All
All
All
All
All
All
All
All
Full/mid
Low
Full/mid
Low
Full/mid
Low
Full/mid
Low
Full/mid
Low
Full/mid
Low
All
All
All
All
Output Data Rate (SPS)
10
50
50
60
12.5
12.5
15
10
50
50
60
50.53
43.64
42.11
36.36
8.4
7.27
53.33
48
44.44
40
8.89
8
27.27
25
20
16.67
REJ60
0
0
1
0
0
1
0
0
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
50 Hz Rejection (dB)2
120 dB (50 Hz and 60 Hz)
120 dB (50 Hz only)
82 dB (50 Hz and 60 Hz)
120 dB (60 Hz only)
120 dB (50 Hz only)
82 dB (50 Hz and 60 Hz)
120 dB (60 Hz only)
100 dB (50 Hz and 60 Hz)
95 dB (50 Hz only)
67 dB (50 Hz and 60 Hz)
95 dB (60 Hz only)
40 dB (60 Hz only)
40 dB (60 Hz only)
40 dB (50 Hz only)
40 dB (50 Hz only)
40 dB (50 Hz and 60 Hz)
40 dB (50 Hz and 60 Hz)
40 dB (60 Hz only)
40 dB (60 Hz only)
40 dB (50 Hz only)
40 dB (50 Hz only)
40 dB (50 Hz and 60 Hz)
40 dB (50 Hz and 60 Hz)
47 dB (50 Hz and 60 Hz)
62 dB (50 Hz and 60 Hz)
85 dB (50 Hz and 60 Hz)
90 dB (50 Hz and 60 Hz)
These calculations assume a stable master clock.
For fast settling mode, the 50 Hz/60 Hz rejection is measured in a band of ±0.5 Hz around 50 Hz and/or 60 Hz. For all other modes, a region of ±1 Hz around 50 Hz
and/or 60 Hz is used.
Rev. A | Page 64 of 90
Data Sheet
AD7124-4
DIAGNOSTICS
The AD7124-4 has numerous diagnostic functions on chip. Use
these features to ensure
is performed, check the status of the REF_DET_ERR bit at the
end of the calibration cycle.
•
•
•
•
•
The reference detect flag may be set when the device exits of
standby mode. Therefore, read the error register after exiting
standby mode to reset the flag to 0.
Read/write operations are to valid registers only
Only valid data is written to the on-chip registers
Appropriate decoupling is used on the LDOs
The external reference, if used, is present
The ADC modulator and filter are working within
specification
CALIBRATION, CONVERSION, AND SATURATION
ERRORS
Functions such as the reference and power supply voltages can
be selected as inputs to the ADC. The AD7124-4 can therefore
check the voltages connected to the device. The AD7124-4 also
generates an internal 20 mV signal that can be applied internally to
a channel by selecting the V_20MV_P to V_20MV_M channel
in the channel register. The PGA can be checked using this
function. As the PGA setting is increased, for example, the
signal as a percent of the analog input range is reduced by a
factor of two. This allows the user to check that the PGA is
functioning correctly.
REFERENCE DETECT
The AD7124-4 includes on-chip circuitry to detect if there is a
valid reference for conversions or calibrations when the user
selects an external reference as the reference source. This is a
valuable feature in applications such as RTDs or strain gages
where the reference is derived externally.
0.7V
OUTPUT: 0 WHEN REFIN ≤0.7V
1 WHEN REFIN <0.7V
13197-128
COMPARATOR
REFIN (REFINx(+) – REFINx(–))
Figure 119. Reference Detect Circuitry
This feature is enabled when the REF_DET_ERR_EN bit in the
ERROR_EN register is set to 1. If the voltage between the
selected REFINx(+) and REFINx(−) pins goes below 0.7 V, or
either the REFINx(+) or REFINx(−) inputs are open circuit, the
AD7124-4 detects that it no longer has a valid reference. In this
case, the REF_DET_ERR bit in the error register is set to 1. The
ERR bit in the status register is also set.
The ADC_CONV_ERR flag is set if there is an overflow or
underflow in the digital filter. The ADC conversion clamps to
all 0s or all 1s also. This flag is updated in conjunction with the
update of the data register and can be cleared only by a read of
the error register.
The ADC_SAT_ERR flag is set if the modulator outputs 20
consecutive 1s or 0s. This indicates that the modulator has
saturated.
When an offset calibration is performed, the resulting offset
coefficient must be between 0x7FFFFF and 0xF80000. If the
coefficient is outside this range, the offset register is not updated
and the ADC_CAL_ERR flag is set. During a full-scale calibration,
overflow of the digital filter is checked. If an overflow occurs,
the error flag is set and the gain register is not updated.
OVERVOLTAGE/UNDERVOLTAGE DETECTION
The overvoltage/undervoltage monitors check the absolute
voltage on the AINx analog input pins. The absolute voltage
must be within specification to meet the datasheet
specifications. If the ADC is operated outside the datasheet
limits, linearity degrades.
If the AD7124-4 is performing normal conversions and the
REF_DET_ERR bit becomes active, the conversion results
revert to all 1s. Therefore, it is not necessary to continuously
monitor the status of the REF_DET_ERR bit when performing
conversions. It is only necessary to verify its status if the
conversion result read from the ADC data register is all 1s.
If the AD7124-4 is performing either offset or full-scale
calibrations and the REF_DET_ERR bit becomes active, the
updating of the respective calibration register is inhibited to
avoid loading incorrect coefficients to the register, and the
REF_DET_ERR bit is set. If the user is concerned about
verifying that a valid reference is in place every time a calibration
Rev. A | Page 65 of 90
OVERVOLTAGE
COMPARATOR
AV DD + 40mV
AINx
AINx_OV_ERR: SET IF AINx IS
40mV ABOVE AVDD
UNDERVOLTAGE
COMPARATOR
AVSS – 40mV
NOTE: AINx IS AINP OR AINM
AINx_UV_ERR: SET IF AINx IS
40mV ABOVE AVSS
13197-129
SIGNAL CHAIN CHECK
The conversion process and calibration process can also be
monitored by the AD7124-4. These diagnostics check the
analog input used as well as the modulator and digital filter
during conversions or calibration. The functions can be enabled
using the ADC_CAL_ERR_EN, ADC_CONV_ERR_EN, and
ADC_SAT_ERR_EN bits in the ERROR_EN register. With these
functions enabled, the ADC_ CAL_ERR, ADC_CONV_ERR, and
ADC_SAT_ERR bits are set if an error occurs.
Figure 120. Analog Input Overvoltage/Undervoltage Monitors
AD7124-4
Data Sheet
The positive (AINP) and negative (AINM) analog inputs can be
separately checked for overvoltages and undervoltages. The
AINP_OV_ERR_EN and AINP_UV_ERR_EN bits in the
ERROR_EN register enable the overvoltage/undervoltage
diagnostics respectively. An overvoltage is flagged when the
voltage on AINP exceeds AVDD while an undervoltage is flagged
when the voltage on AINP goes below AVSS. Similarly, an
overvoltage/undervoltage check on the negative analog input
pin is enabled using the AINM_OV_ERR_EN and AINM_UV_
ERR_EN bits in the ERROR_EN register. The error flags are
AINP_OV_ERR, AINP_UV_ERR, AINM_OV_ERR, and
AINM_UV_ERR in the error register.
When this function is enabled, the corresponding flags may be
set in the error register. Therefore, the user must read the error
register when the overvoltage/undervoltage checks are enabled
to ensure that the flags are reset to 0.
POWER SUPPLY MONITORS
Along with converting external voltages, the ADC can monitor
the voltage on the AVDD pin and the IOVDD pin. When the
inputs of AVDD to AVSS or IOVDD to DGND are selected, the
voltage (AVDD to AVSS or IOVDD to DGND) is internally
attenuated by 6, and the resulting voltage is applied to the Σ-Δ
modulator. This is useful because variations in the power supply
voltage can be monitored.
LDO MONITORING
There are several LDO checks included on the AD7124-4. Like
the external power supplies, the voltage generated by the analog
and digital LDOs are selectable as inputs to the ADC. In addition,
the AD7124-4 can continuously monitor the LDO voltages.
Power Supply Monitor
The voltage generated by the ALDO and DLDO can be
monitored by enabling the ALDO_PSM_ERR_EN bit and the
DLDO_PSM_ERR_EN bit, respectively, in the ERROR_EN
register. When enabled, the output voltage of the LDO is
continuously monitored. If the ALDO voltage drops below
1.6 V, the ALDO_PSM_ERR flag is asserted. If the DLDO
voltage drops below 1.55 V, the DLDO_PSM_ERR flag is
asserted. The bit remains set until the corresponding LDO
voltage recovers. However, the bit is only cleared when the
error register is read.
ALDO
SET IF ALDO OUTPUT VOLTAGE IS
LESS THAN 1.6V
1.6V
13197-130
OVERVOLTAGE
COMPARATOR
Figure 121. Analog LDO Monitor
SET IF DLDO OUTPUT VOLTAGE IS
LESS THAN 1.55V
The analog and digital LDOs require an external decoupling
capacitor of 0.1 µF. The AD7124-4 can check for the presence of
this decoupling capacitor. Using the LDO_CAP_CHK bits in
the ERROR_EN register, the LDO being checked is turned off
and the voltage at the LDO output is monitored. If the voltage
falls, this is considered a fail and the LDO_CAP_ERR bit in the
error register is set.
Only the analog LDO or digital LDO can be tested for the
presence of the decoupling capacitor at any one time. This test
also interferes with the conversion process.
The circuitry used to check for missing decoupling capacitors
can also be tested by the AD7124-4. When the LDO_CAP_
CHK_TEST_EN bit in the ERROR_EN register is set, the
decoupling capacitor is internally disconnected from the LDO,
forcing a fault condition. Therefore, when the LDO capacitor
test is performed, a fault condition is reported, that is, the
LDO_CAP_ERR bit in the error register is set.
MCLK COUNTER
A stable master clock is important as the output data rate, filter
settling time, and the filter notch frequencies are dependent on
the master clock. The AD7124-4 allows the user to monitor the
master clock. When the MCLK_CNT_EN bit in the ERROR_EN
register is set, the MCLK_COUNT register increments by 1 every
131 master clock cycles. The user can monitor this register over
a fixed period of time. The master clock frequency can be
determined from the result in the MCLK_COUNT register.
The MCLK_COUNT register wraps around after it reaches its
maximum value.
SPI SCLK COUNTER
The SPI SCLK counter counts the number of SCLK pulses used
in each read and write operation. CS must frame every read and
write operation when this function is used. All read and write
operations are multiples of eight SCLK pulses (8, 16, 32, 40, 48).
If the SCLK counter counts the SCLK pulses and the result is not a
multiple of eight, an error is flagged; the SPI_SCLK_CNT_ERR bit
in the error register is set. If a write operation is being performed
and the SCLK contains an incorrect number of SCLK pulses,
the value is not written to the addressed register and the write
operation is aborted.
13197-131
1.55V
LDO Capacitor Detect
The SCLK counter is enabled by setting the SPI_SCLK_
CNT_ERR_EN bit in the ERROR_EN register.
OVERVOLTAGE
COMPARATOR
DLDO
The AD7124-4 can also test the circuitry used for the power
supply monitoring. When the ALDO_PSM_TRIP_TEST_EN or
DLDO_PSM_TRIP_TEST_EN bits are set, the input to the test
circuitry is tied to GND rather than the LDO output. Set the
corresponding ALDO_PSM_ERR or DLDO_PSM_ERR bit.
Figure 122. Digital LDO Monitor
Rev. A | Page 66 of 90
Data Sheet
AD7124-4
DIN
Any read or write operations performed when SPI_IGNORE_ERR
is enabled are ignored.
CHECKSUM PROTECTION
The AD7124-4 has a checksum mode that can be used to improve
interface robustness. Using the checksum ensures that only
valid data is written to a register and allows data read from a
register to be validated. If an error occurs during a register
write, the CRC_ERR bit is set in the error register. However, to
ensure that the register write was successful, read back the
register and verify the checksum.
For CRC checksum calculations, the following polynomial is
always used:
The checksum is appended to the end of each read and write
transaction. The checksum calculation for the write transaction
is calculated using the 8-bit command word and the 8-bit to 24-bit
data. For a read transaction, the checksum is calculated using the
CS
DATA
CRC
8-BIT COMMAND
UP TO 32-BIT OUTPUT
8-BIT CRC
CS
DIN
CMD
DATA
CRC
SCLK
Figure 124. SPI Read Transaction with CRC
If checksum protection is enabled when continuous read mode
is active, there is an implied read data command of 0x42 before
every data transmission that must be accounted for when
calculating the checksum value. This ensures a nonzero checksum
value even if the ADC data equals 0x000000.
MEMORY MAP CHECKSUM PROTECTION
For added robustness, a CRC calculation is performed on the
on-chip registers as well. The status register, data register, and
MCLK counter register are not included in this check as their
contents change continuously. The CRC is performed at a rate
of 1/2400 seconds. Each time that the memory map is accessed,
the CRC is recalculated. Events which cause the CRC to be
recalculated are
•
•
•
x8 + x2 + x + 1
The CRC_ERR_EN bit in the ERROR_EN register enables and
disables the checksum.
8-BIT CRC
Figure 123. SPI Write Transaction with CRC
DOUT/
RDY
At certain times, the on-chip registers are not accessible. For
example, during power-up, the on-chip registers are set to their
default values. The user must wait until this operation is
complete before reading from or writing to registers. Also, when
offset or gain calibrations are being performed, registers cannot
be accessed. The SPI_IGNORE_ERR bit in the error register
indicates when the on-chip registers cannot be accessed. This
diagnostic is enabled by default. The function can be disabled
using the SPI_IGNORE_ERR_EN bit in the ERROR_EN register.
UP TO 24-BIT INPUT
SCLK
This function, along with the SCLK counter and the CRC,
makes the serial interface more robust. Invalid registers are not
written to or read from. An incorrect number of SCLK pulses
can cause the serial interface to go asynchronous and incorrect
registers to be accessed. The AD7124-4 protects against these
issues via the diagnostics.
SPI_IGNORE ERROR
8-BIT COMMAND
CS
13197-132
Along with the SCLK counter, the AD7124-4 can also check the
read and write operations to ensure that valid registers are being
addressed. When the SPI_READ_ERR_EN bit or the SPI_
WRITE_ERR_EN bit in the ERROR_EN register are set, the
AD7124-4 checks the address of the read/write operations. If
the user attempts to write to or read from any register other
than the user registers described in this data sheet, an error is
flagged; the SPI_READ_ERR bit or the SPI_WRITE_ERR bit in
the error register is set and the read/write operation is aborted.
command word and the 8-bit to 32-bit data output. Figure 123 and
Figure 124 show SPI write and read transactions, respectively.
13197-133
SPI READ/WRITE ERRORS
•
A user write
An offset/full-scale calibration
When the device is operated in single conversion mode
and the ADC goes into idle mode following the completion
of the conversion
When exiting continuous read mode (the CONT_READ bit
in the ADC_CONTROL register is set to 0)
The memory map CRC function is enabled by setting the
MM_CRC_ERR_EN bit in the ERROR_EN register to 1. If an
error occurs, the MM_CRC_ERR bit in the error register is set
to 1.
Rev. A | Page 67 of 90
AD7124-4
Data Sheet
CRC Calculation
The checksum, which is 8 bits wide, is generated using the polynomial
x8 + x2 + x + 1
To generate the checksum, the data is left shifted by eight bits to create a number ending in eight Logic 0s. The polynomial is aligned so that
its MSB is adjacent to the leftmost Logic 1 of the data. An XOR (exclusive OR) function is applied to the data to produce a new, shorter
number. The polynomial is again aligned so that its MSB is adjacent to the leftmost Logic 1 of the new result, and the procedure is repeated. This
process is repeated until the original data is reduced to a value less than the polynomial. This is the 8-bit checksum.
Example of a Polynomial CRC Calculation—24-Bit Word: 0x654321 (8-Bit Command and 16-Bit Data)
An example of generating the 8-bit checksum using the polynomial based checksum is as follows:
Initial value
011001010100001100100001
x +x +x+1
8
2
01100101010000110010000100000000
left shifted eight bits
=
polynomial
100000111
100100100000110010000100000000
XOR result
100000111
polynomial
100011000110010000100000000
XOR result
100000111
polynomial
11111110010000100000000
XOR result
100000111
polynomial value
1111101110000100000000
XOR result
100000111
polynomial value
111100000000100000000
XOR result
100000111
polynomial value
11100111000100000000
XOR result
100000111
polynomial value
1100100100100000000
XOR result
100000111
polynomial value
100101010100000000
XOR result
100000111
polynomial value
101101100000000
XOR result
100000111
polynomial value
1101011000000
100000111
XOR result
polynomial value
101010110000
XOR result
100000111
polynomial value
1010001000
XOR result
100000111
polynomial value
10000110
checksum = 0x86
Rev. A | Page 68 of 90
Data Sheet
AD7124-4
BURNOUT CURRENTS
The AD7124-4 contains two constant current generators that
can be programmed to 0.5 µA, 2 µA, or 4 µA. One generator
sources current from AVDD to AINP, and one sinks current from
AINM to AVSS. These currents enable open wire detection.
AVDD
TEMPERATURE SENSOR
Embedded in the AD7124-4 is a temperature sensor that is
useful to monitor the die temperature. This is selected using the
AINP[4:0] and AINM[4:0] bits in the channel register. The
sensitivity is 13,584 codes/°C, approximately. The equation for
the temperature sensor is
PGA1
AVSS
13197-134
Temperature (°C) = ((Conversion − 0x800000)/13,584) − 272.5
The temperature sensor has an accuracy of ±0.5°C typically.
1.2
The currents are switched to the selected analog input pair.
Both currents are either on or off. The burnout bits in the
configuration register enable/disable the burnout currents along
with setting the amplitude. Use these currents to verify that an
external transducer is still operational before attempting to take
measurements on that channel. After the burnout currents are
turned on, they flow in the external transducer circuit, and a
measurement of the input voltage on the analog input channel
can be taken. If the resulting voltage measured is near full scale,
the user must verify why this is the case. A near full-scale reading
can mean that the front-end sensor is open circuit. It can also
mean that the front-end sensor is overloaded and is justified in
outputting full scale, or that the reference may be absent and the
REF_DET_ERR bit is set, thus clamping the data to all 1s.
1.0
TEMPERATURE SENSOR ERROR (°C)
Figure 125. Burnout Currents
Rev. A | Page 69 of 90
32 UNITS
0.8
0.6
0.4
0.2
0
–0.2
–0.4
–0.6
–40 –30 –20 –10
0
15
25
40
50
60
70
85
95 105
TEMPERATURE (°C)
Figure 126. Temperature Sensor Error vs. Temperature
13197-135
X-MUX
BURNOUT
DETECT
When a conversion is close to full scale, the user must check
these three cases before making a judgment. If the voltage
measured is 0 V, it may indicate that the transducer has short
circuited. For normal operation, these burnout currents are
turned off by setting the burnout bits to zero. The current
sources work over the normal absolute input voltage range
specifications with buffers on.
AD7124-4
Data Sheet
GROUNDING AND LAYOUT
The analog inputs and reference inputs are differential and,
therefore, most of the voltages in the analog modulator are
common-mode voltages. The high common-mode rejection of
the device removes common-mode noise on these inputs. The
analog and digital supplies to the AD7124-4 are independent
and separately pinned out to minimize coupling between the
analog and digital sections of the device. The digital filter
provides rejection of broadband noise on the power supplies,
except at integer multiples of the master clock frequency.
The digital filter also removes noise from the analog and
reference inputs, provided that these noise sources do not
saturate the analog modulator. As a result, the AD7124-4 is
more immune to noise interference than a conventional high
resolution converter. However, because the resolution of the
AD7124-4 is high and the noise levels from the converter are so
low, care must be taken with regard to grounding and layout.
The PCB that houses the ADC must be designed so that the
analog and digital sections are separated and confined to
certain areas of the board. A minimum etch technique is
generally best for ground planes because it results in the best
shielding.
In any layout, the user must keep in mind the flow of currents
in the system, ensuring that the paths for all return currents are as
close as possible to the paths the currents took to reach their
destinations.
Avoid running digital lines under the device because this
couples noise onto the die and allows the analog ground plane
to run under the AD7124-4 to prevent noise coupling. The
power supply lines to the AD7124-4 must use as wide a trace as
possible to provide low impedance paths and reduce glitches on
the power supply line. Shield fast switching signals like clocks
with digital ground to prevent radiating noise to other sections
of the board and never run clock signals near the analog inputs.
Avoid crossover of digital and analog signals. Run traces on
opposite sides of the board at right angles to each other. This
reduces the effects of feedthrough on the board. A microstrip
technique is by far the best but is not always possible with a
double-sided board. In this technique, the component side of
the board is dedicated to ground planes, whereas signals are
placed on the solder side.
Good decoupling is important when using high resolution ADCs.
The AD7124-4 has two power supply pins—AVDD and IOVDD.
The AVDD pin is referenced to AVSS, and the IOVDD pin is
referenced to DGND. Decouple AVDD with a 1 µF tantalum
capacitor in parallel with a 0.1 µF capacitor to AVSS on each pin.
Place the 0.1 µF capacitor as close as possible to the device on
each supply, ideally right up against the device. Decouple IOVDD
with a 1 µF tantalum capacitor in parallel with a 0.1 µF
capacitor to DGND. All analog inputs must be decoupled to
AVSS. If an external reference is used, decouple the REFINx(+)
and REFINx(−) pins to AVSS.
The AD7124-4 also has two on-board LDO regulators—one
that regulates the AVDD supply and one that regulates the IOVDD
supply. For the REGCAPA pin, it is recommended that a 0.1 µF
capacitor to AVSS be used. Similarly, for the REGCAPD pin, it is
recommended that a 0.1 µF capacitor to DGND be used.
If using the AD7124-4 with split supply operation, a separate
plane must be used for AVSS.
Rev. A | Page 70 of 90
Data Sheet
AD7124-4
APPLICATIONS INFORMATION
Most conversions are read from the thermocouple, with the
cold junction being read only periodically as the cold junction
temperature is stable or slow moving. If a T-type thermocouple
is used, it can measure a temperature from −200°C to +400°C.
The voltage generated over this temperature range is −8.6 mV
to +17.2 mV. The AD7124-4 internal reference equals 2.5 V.
Therefore, the PGA is set to 128. If the thermocouple uses the
AIN0/AIN1 channel and the thermistor is connected to the
AIN4/AIN5 channel, the conversion process is as follows:
The AD7124-4 offers a low cost, high resolution analog-todigital function. Because the analog-to-digital function is provided
by a Σ-Δ architecture, the device is more immune to noisy
environments, making it ideal for use in sensor measurement,
and industrial and process control applications.
TEMPERATURE MEASUREMENT USING A
THERMOCOUPLE
Figure 127 outlines a connection from a thermocouple to the
AD7124-4. In a thermocouple application, the voltage generated
by the thermocouple is measured with respect to an absolute
reference; thus, the internal reference is used for this conversion.
The cold junction measurement uses a ratiometric configuration,
so the reference is provided externally.
1.
2.
Reset the ADC.
Select the power mode.
Set the CHANNEL_0 register analog input to AIN0/AIN1.
Assign Setup 0 to this channel. Configure Setup 0 to have a
gain of 128 and select the internal reference. Select the
filter type and set the output data rate.
3. Enable VBIAS on AIN0.
4. Set the CHANNEL_1 register analog input to AIN4/AIN5.
Assign Setup 1 to this channel. Configure Setup 1 to have a
gain of 1 and select the external reference REFIN2(±).
Select the filter type and set the output data rate.
5. Enable the excitation current (IOUTx) and select a suitable
value. Output this current to the AIN4 pin.
6. Enable the AIN0/AIN1 channel. Wait until RDY goes low.
Read the conversion.
7. Continue to read nine further conversions from the
AIN0/AIN1 channel.
8. Disable CHANNEL_0 and enable CHANNEL_1.
9. Wait until RDY goes low. Read one conversion.
10. Repeat Step 5 to Step 8.
Because the signal from the thermocouple is small, the AD7124-4
is operated with the PGA enabled to amplify the signal from the
thermocouple. As the input channel is buffered, large decoupling
capacitors can be placed on the front end to eliminate any noise
pickup that may be present in the thermocouple leads. The bias
voltage generator provides a common-mode voltage so that the
voltage generated by the thermocouple is biased up to (AVDD −
AVSS)/2. For thermocouple voltages that are centered about ground,
the AD7124-4 can be operated with a split power supply (±1.8 V).
The cold junction compensation is performed using a thermistor in
Figure 127. The on-chip excitation current supplies the thermistor.
In addition, the reference voltage for the cold junction measurement
is derived from a precision resistor in series with the thermistor.
This allows a ratiometric measurement so that variation of the
excitation current has no effect on the measurement (it is the
ratio of the precision reference resistance to the thermistor
resistance that is measured).
Using the linearization equation for the T-type thermocouple,
process the thermocouple voltage along with the thermistor voltage
and compute the actual temperature at the thermocouple head.
AVDD
THERMOCOUPLE JUNCTION
R
R
C
C
AVDD
REFIN1(+)
AIN0
AIN1
VBIAS
RREF
REFERENCE
DETECT
AVDD
AIN4
X-MUX
AIN5
REFIN2(+)
REFIN2(–)
COLD JUNCTION
BAND GAP
REFERENCE
Σ-Δ
ADC
PGA
AVSS
SERIAL
INTERFACE
AND
CONTROL
LOGIC
CHANNEL
SEQUENCER
TEMP
SENSOR
VDD
REFIN1(–)
PSW
DIGITAL
FILTER
DIAGNOSTICS
DOUT/RDY
DIN
SCLK
CS
IOVDD
INTERNAL
CLOCK
CLK
SYNC
NOTES
1. SIMPLIFIED BLOCK DIAGRAM SHOWN.
REGCAPA
Figure 127. Thermocouple Application
Rev. A | Page 71 of 90
REGCAPD
AVSS
DGND
13197-136
AD7124-4
AD7124-4
Data Sheet
The external antialias filter is omitted for clarity. However, such
a filter is required to reject any interference at the modulator
frequency and multiples of the modulator frequency. In addition,
some filtering may be needed for EMI purposes. Both the analog
inputs and the reference inputs can be buffered, which allows
the user to connect any RC combination to the reference or
analog input pins.
The required power mode depends on the performance
required from the system along with the current consumption
allowance for the system. In a field transmitter, low current
consumption is essential. In this application, the low power
mode or mid power mode is most suitable. In process control
applications, power consumption is not a priority. Thus, full
power mode may be selected. The full power mode offers
higher throughput and lower noise.
The AD7124-4 on-chip diagnostics allow the user to check the
circuit connections, monitor power supply, reference, and LDO
voltages, check all conversions and calibrations for any errors, as
well as monitor any read/write operations. In thermocouple
applications, the circuit connections are verified using the
reference detect and the burnout currents. The REF_DET_ERR
flag is set if the external reference REFIN2(±) is missing. The
burnout currents (available in the configuration registers) detect an
open wire. For example, if the thermocouple is not connected
and the burnout currents are enabled on the channel, the ADC
outputs a conversion that is equal to or close to full scale. For
best performance, enable the burnout currents periodically to
check the connections but disable them as soon as the connections
are verified for they add an error to the conversions. The
decoupling capacitors on the LDOs can also be checked. The
ADC indicates if the capacitor is not present.
As part of the conversion process, the analog input overvoltage/
undervoltage monitors are useful for detecting any excessive
voltages on AINP and AINM. The power supply voltages and
reference voltages are selectable as inputs to the ADC. Thus, the
user can periodically check these voltages to confirm whether
they are within the system specification. Also, the user can check
that the LDO voltages are within specification. The conversion
process and calibration process can also be checked. This ensures
that any invalid conversions or calibrations are flagged to the user.
Finally, the CRC check, SCLK counter, and the SPI read/write
checks make the interface more robust as any read/write
operation that is not valid is detected. The CRC check
highlights if any bits are corrupted when being transmitted
between the processor and the ADC.
TEMPERATURE MEASUREMENT USING AN RTD
To optimize a 3-wire RTD configuration, two identically
matched current sources are required. The AD7124-4, which
contains two well matched current sources, is ideally suited to
these applications. One possible 3-wire configuration is shown
in Figure 128. In this 3-wire configuration, the lead resistances
result in errors if only one current (output at AIN0) is used, as
the excitation current flows through RL1, developing a voltage
error between AIN1 and AIN2. In the scheme outlined, the
second RTD current source (available at AIN3) compensates for
the error introduced by the excitation current flowing through
RL1. The second RTD current flows through RL2. Assuming
that RL1 and RL2 are equal (the leads are normally of the same
material and of equal length) and that the excitation currents
match, the error voltage across RL2 equals the error voltage
across RL1, and no error voltage is developed between AIN1
and AIN2. Twice the voltage is developed across RL3; however,
because this is a common-mode voltage it does not introduce
errors. The reference voltage for the AD7124-4 is also generated
using one of the matched current sources. It is developed using
a precision resistor and applied to the differential reference pins
of the ADC. This scheme ensures that the analog input voltage
span remains ratiometric to the reference voltage. Any errors in
the analog input voltage due to the temperature drift of the
excitation current are compensated by the variation of the
reference voltage.
As an example, the PT100 measures temperature from −200°C
to +600°C. The resistance is 100 Ω typically at 0°C and 313.71 Ω
at 600°C. If the 500 µA excitation currents are used, the
maximum voltage generated across the RTD when using the full
temperature range of the RTD is
500 µA × 313.71 Ω = 156.86 mV
This is amplified to 2.51 V within the AD7124-4 if the gain is
programmed to 16.
The voltage generated across the reference resistor must be at least
2.51 V. Therefore, the reference resistor value must equal at least
2.51 V/500 µA = 5020 Ω
Therefore, a 5.11 kΩ resistor can be used.
5.11 kΩ × Excitation Current = 5.11 kΩ × 500 µA = 2.555 V
One other consideration is the output compliance. The output
compliance equals AVDD − 0.37 V. If a 3.3 V analog supply is
used, the voltage at AIN0 must be less than (3.3 V − 0.37 V) =
2.93 V. From the previous calculations, this specification is met
because the maximum voltage at AIN0 equals the voltage across
the reference resistor plus the voltage across the RTD, which equals
2.555 V + 156.86 mV = 2.712 V
Rev. A | Page 72 of 90
Data Sheet
AD7124-4
The power mode to use depends on the performance required
from the system along with the current consumption allowance
for the system. In a field transmitter, low current consumption
is essential. In this application, the low power mode or mid power
mode is most suitable. In process control applications, power
consumption is not a priority. Thus, full power mode may be
selected. The full power mode offers higher throughput and
lower noise.
A typical procedure for reading the RTD is as follows:
4.
5.
6.
Reset the ADC.
Select the power mode.
Set the CHANNEL_0 register analog input to AIN1/AIN2.
Assign Setup 0 to this channel. Configure Setup 0 to have a
gain of 16 and select the reference source REFIN2(±).
Select the filter type and set the output data rate.
Program the excitation currents to 500 µA and output the
currents on the AIN0 and AIN3 pins.
Wait until RDY goes low. Read the conversion value.
Repeat Step 4.
The AD7124-4 on-chip diagnostics allow the user to check the
circuit connections, monitor the power supply, reference, and
LDO voltages, check all conversions and calibrations for any
errors, as well as monitor any read/write operations. In RTD
applications, the circuit connections are verified using the
reference detect and the burnout currents. The REF_DET_ERR
flag is set if the external reference REFIN2(±) is missing. The
burnout currents (available in the configuration registers) detect an
open wire. The decoupling capacitors on the LDOs can also be
checked. The ADC indicates if the capacitor is not present.
In the processor, implement the linearization routine for the
PT100.
The external antialias filter is omitted for clarity. However, such
a filter is required to reject any interference at the modulator
frequency and multiples of the modulator frequency. Also, some
filtering may be needed for EMI purposes. Both the analog inputs
and reference inputs can be buffered, which allows the user to
connect any RC combination to the reference or analog input pins.
As part of the conversion process, the analog input overvoltage/
undervoltage monitors are useful to detect any excessive voltages
on AINP and AINM. The power supply voltages and reference
voltages are selectable as inputs to the ADC. Thus, the user can
periodically check these voltages to confirm whether they are
within the system specification. Also, the user can check that
the LDO voltages are within specification. The conversion process
and calibration process can also be checked. This ensures that
any invalid conversions or calibrations are flagged to the user.
On the AD7124-4, the excitation currents can be made available
at the input pins, for example, the AIN3 pin can function as an
analog input as well as outputting the current source. This option
allows multiple sensors to be connected to the ADC using a
minimum pin count. However, the resistor of the antialiasing
filter is in series with the RTD. This introduces an error in the
conversions as there is a voltage generated across the antialiasing
resistor. To minimize the error, minimize the resistance of the
antialiasing filter.
Finally, the CRC check, SCLK counter, and the SPI read/write
checks make the interface more robust as any read/write
operation that is not valid is detected. The CRC check highlights if
any bits are corrupted when being transmitted between the
processor and the ADC.
AVDD
AVDD
REFIN1(+)
VBIAS
AIN0
AVDD
REFIN2(+)
RREF
REFERENCE
DETECT
REFIN2(–)
PGA
X-MUX
RL1
RTD
RL2
AIN1
AIN2
AIN3
RL3
REFIN1(–)
Σ-Δ
ADC
AVSS
DIGITAL
FILTER
SERIAL
INTERFACE
AND
CONTROL
LOGIC
CHANNEL
SEQUENCER
TEMP
SENSOR
VDD
DIAGNOSTICS
DOUT/RDY
DIN
SCLK
CS
IOVDD
INTERNAL
CLOCK
CLK
PSW
SYNC
AD7124-4
NOTES
1. SIMPLIFIED BLOCK DIAGRAM SHOWN.
REGCAPA
Figure 128. 3-Wire RTD Application
Rev. A | Page 73 of 90
REGCAPD
AVSS
DGND
13197-137
1.
2.
3.
AD7124-4
Data Sheet
FLOWMETER
A typical procedure for reading the sensors is as follows:
Figure 129 shows the AD7124-4 being used in a flowmeter
application that consists of two pressure transducers, with the
rate of flow being equal to the pressure difference. The pressure
transducers are arranged in a bridge network and give a differential
output voltage between its OUT+ and OUT− terminals. With
rated full-scale pressure (in this case, 300 mmHg) on the
transducer, the differential output voltage is 3 mV/V of the input
voltage (that is, the voltage between the IN+ and IN−
terminals).
1.
2.
3.
Assuming a 3 V excitation voltage, the full-scale output range
from the transducer is 9 mV. The excitation voltage for the
bridge can directly provide the reference for the ADC, as the
reference input range includes the supply voltage.
A second advantage of using the AD7124-4 in transducer-based
applications is that the low-side power switch can be fully utilized
in low power applications. The low-side power switch is connected
in series with the cold side of the bridges. In normal operation,
the switch is closed and measurements are taken. In applications
where power is of concern, the AD7124-4 can be placed in standby
mode, thus significantly reducing the power consumed in the
application. In addition, the low-side power switch can be opened
while in standby mode, thus avoiding unnecessary power
consumption by the front-end transducers. When the device is
taken out of standby mode, and the low-side power switch is
closed, the user must ensure that the front-end circuitry is fully
settled before attempting a read from the AD7124-4. The power
switch can be closed prior to taking the device out of standby, if
needed. This allows time for the sensor to power up and settle
before the ADC powers up and begins sampling the analog input.
In the diagram, temperature compensation is performed using a
thermistor. The on-chip excitation current supplies the thermistor.
In addition, the reference voltage for the temperature measurement
is derived from a precision resistor in series with the thermistor.
This allows a ratiometric measurement so that variation of the
excitation current has no effect on the measurement (it is the
ratio of the precision reference resistance to the thermistor
resistance that is measured).
If the sensor sensitivity is 3 mV/V and the excitation voltage is 3 V,
the maximum output from the sensor is 9 mV. The AD7124-4
PGA can be set to 128 to amplify the sensor signal.
The AD7124-4 PGA amplifies the signal to
9 mV × 128 = 1.152 V
This value does not exceed the reference voltage (3 V).
Reset the ADC.
Select the power mode.
Set the CHANNEL_0 register analog input to AIN0/AIN1.
Assign Setup 0 to this channel. Configure Setup 0 to have a
gain of 128 and select the reference source to REFIN1(±).
Select the filter type and set the output data rate.
4. Set the CHANNEL_1 register analog input to AIN2/AIN3.
Assign Setup 0 to this channel (both channels use the same
setup).
5. Set the CHANNEL_2 register analog input to AIN4/AIN5.
Assign Setup 1 to this channel. Configure Setup 1 to have a
gain of 1 and select the reference source REFIN2(±). Select
the filter type and set the output data rate.
6. Program the excitation current and output the current on
the AIN4 pin.
7. Enable both CHANNEL_0 and CHANNEL_1. Enable the
DATA_STATUS bit to identify the channel from which the
conversion originated. The ADC automatically sequences
through these channels.
8. Wait until RDY goes low. Read the conversion value.
9. Repeat Step 8 until the temperature is to be read (every 10
conversions of the pressure sensor readings, for example).
10. Disable CHANNEL_0 and CHANNEL_1. Enable
CHANNEL_2.
11. Wait until RDY goes low. Read the conversion.
12. Repeat Step 6 to Step 10.
In the processor, the conversion information is converted to
pressure and the flow rate can be calculated. The processor
typically contains a lookup table for each pressure sensor so its
variation with temperature can be compensated.
The external antialias filter is omitted for clarity. However, such
a filter is required to reject any interference at the modulator
frequency and multiples of the modulator frequency. Also,
some filtering may be needed for EMI purposes. Both the
analog inputs and reference inputs can be buffered, which
allows the user to connect any RC combination to the reference
or analog input pins.
The power mode to use depends on the performance required
from the system along with the current consumption allowance
for the system. In a field transmitter, low current consumption
is essential. In this application, low power mode or mid power
mode is most suitable. In process control applications, power
consumption is not a priority. Thus, full power mode may be
selected. Full power mode offers higher throughput and lower
noise.
Rev. A | Page 74 of 90
Data Sheet
AD7124-4
The AD7124-4 on-chip diagnostics allow the user to check the
circuit connections, monitor power supply, reference, and LDO
voltages, check all conversions and calibrations for any errors, as
well as monitor any read/write operations. The REF_DET_ERR
flag is set if the external reference REFIN2(±) or REFIN1(±) is
missing. The decoupling capacitors on the LDOs can also be
checked. The ADC indicates if the capacitor is not present.
As part of the conversion process, the analog input
overvoltage/undervoltage monitors are useful to detect any
excessive voltages on AINP and AINM. The power supply
voltages and reference voltages are selectable as inputs to the
ADC. Thus, the user can periodically check these voltages to
confirm whether they are within the system specification. In
addition, the user can check that the LDO voltages are within
specification. The conversion process and calibration process
can also be checked. This ensures that any invalid conversions
or calibrations are flagged to the user.
Finally, the CRC check, SCLK counter, and the SPI read/write
checks make the interface more robust as any read/write
operation that is not valid is detected. The CRC check
highlights if any bits are corrupted when being transmitted
between the processor and the ADC.
AVDD
IN+
OUT–
OUT+
IN–
OUT+
IN–
VBIAS
AIN0
AIN1
AIN2
AIN3
AIN4
AIN5
REFIN2(+) X-MUX
REFIN2(–)
RREF
REFERENCE
DETECT
AVDD
Σ-Δ
ADC
PGA
AVSS
SERIAL
INTERFACE
AND
CONTROL
LOGIC
CHANNEL
SEQUENCER
TEMP
SENSOR
VDD
REFIN1(–)
PSW
DIGITAL
FILTER
DIAGNOSTICS
DOUT/RDY
DIN
SCLK
CS
IOVDD
INTERNAL
CLOCK
CLK
SYNC
AD7124-4
AVSS
REGCAPA
NOTES
1. SIMPLIFIED BLOCK DIAGRAM SHOWN.
Figure 129. Flowmeter Application
Rev. A | Page 75 of 90
REGCAPD
AVSS
DGND
13197-138
OUT–
AVDD
REFIN1(+)
IN+
AD7124-4
Data Sheet
ON-CHIP REGISTERS
The ADC is controlled and configured via a number of on-chip registers that are described in the following sections. In the following
descriptions, set implies a Logic 1 state and cleared implies a Logic 0 state, unless otherwise noted.
Table 63. Register Summary
Addr. Name
0x00 COMMS
Bit 7
WEN
Bit 6
R/W
Bit 5
0x00
Status
RDY
ERROR_FLAG
0x01
ADC_
CONTROL
0x02
Data
0x03
IO_
CONTROL_1
GPIO_DAT2
PDSW
GPIO_DAT1
0
0x04
IO_
CONTROL_2
VBIAS7
0
VBIAS6
0
0x05
0x06
ID
Error
Bit 4
0
0x08
0x09
to
0x18
0x19
to
0x20
0x21
to
0x28
ERROR_EN
FILTER_0 to
FILTER_7
0x29
to
0x30
OFFSET_0 to
OFFSET_7
0x31
to
0x38
GAIN_0 to
GAIN_7
1
0
CONT_READ
CS_EN
IOUT1_CH
0
VBIAS3
DEVICE_ID
0
0
VBIAS2
GPIO_CTRL1
ALDO_PSM_
ERR
0
SPI_IGNORE_
ERR
MCLK_CNT_EN
AINP_OV_ERR_
EN
ALDO_PSM_
ERR_EN
AINP_UV_ERR_
EN
SPI_IGNORE_
ERR_EN
SPI_SCLK_CNT_
ERR
LDO_CAP_CHK_
TEST_EN
AINM_OV_ERR_
EN
SPI_SCLK_CNT_
ERR_EN
Reset
0x00
RW
W
0x00
R
REF_EN
0x0000
RW
0x000000
R
0
0
0x000000
RW
0
VBIAS0
0x0000
RW
0x02
0x000000
R
R
0x000040
RW
0x00
R
0x80011
RW
REF_BUFP
0x0860
RW
SINGLE_CYCLE
0x060180
RW
0x800000
RW
0x5XXXXX
RW
IOUT0
VBIAS5
0
AINM_UV_
REF_DET_ERR
ERR
SPI_READ_
SPI_WRITE_
ERR
ERR
LDO_CAP_CHK
AINM_UV_
REF_DET_ERR_
ERR_EN
EN
SPI_READ_
SPI_WRITE_
ERR_EN
ERR_EN
MCLK_COUNT
Setup
IOUT0_CH
0
VBIAS1
SILICON_REVISION
ADC_CAL_ERR
ADC_CONV_
ERR
0
DLDO_PSM_
ERR
SPI_CRC_ERR
MM_CRC_ERR
0
ADC_CAL_ERR_
EN
DLDO_PSM_
TRIP_TEST_EN
SPI_CRC_ERR_EN
ADC_SAT_
ERR_EN
ALDO_PSM_
TRIP_TEST_EN
0
VBIAS4
0
LDO_CAP_ERR
AINM_OV_ERR
Bit 0
CLK_SEL
IOUT1
AINP_UV_ERR
ADC_CONV_
ERR_EN
DLDO_PSM_
ERR_EN
MM_CRC_ERR_
EN
0
AINP[2:0]
AIN_BUFP
DATA_STATUS
Mode
Data [23:16]
Data [15:8]
Data [7:0]
GPIO_CTRL2
0
Bit 1
CH_ACTIVE
DOUT_RDY_
DEL
AINP_OV_ERR
MCLK_
COUNT
CHANNEL_0
Enable
to
CHANNEL_15
CONFIG_0 to
CONFIG_7
REF_BUFM
Bit 2
RS[5:0]
POR_FLAG
0
POWER_MODE
0x07
Bit 3
ADC_SAT_ERR
0
AINP[4:3]
AINM[4:0]
0
AIN_BUFM
Filter
Bipolar
REF_SEL
REJ60
Burnout
PGA
POST_FILTER
0
FS[10:8]
FS[7:0]
Offset [23:16]
Offset [15:8]
Offset [7:0]
Gain [23:16]
Gain [15:8]
Gain [7:0]
CHANNEL_0 is reset to 0x8001. All other channels are reset to 0x0000.
Rev. A | Page 76 of 90
Data Sheet
AD7124-4
COMMUNICATIONS REGISTER
RS[5:0] = 0, 0, 0, 0, 0, 0
The communications register is an 8-bit, write only register. All
communications to the device must start with a write operation
to the communications register. The data written to the communications register determines whether the next operation is a read
or write operation, and to which register this operation takes
place, the RS[5:0] bits selecting the register to be accessed.
For read or write operations, after the subsequent read or write
operation to the selected register is complete, the interface
returns to where it expects a write operation to the
Bit 7
WEN (0)
Bit 6
R/W (0)
Bit 5
Bit 4
communications register. This is the default state of the interface
and, on power-up or after a reset, the ADC is in this default
state waiting for a write operation to the communications
register.
In situations where the interface sequence is lost, a write
operation of at least 64 serial clock cycles with DIN high returns
the ADC to this default state by resetting the entire device.
Table 64 outlines the bit designations for the communications
register. Bit 7 denotes the first bit of the data stream.
Bit 3
Bit 2
RS[5:0] (0)
Bit 1
Bit 0
Table 64. Communications Register Bit Descriptions
Bits
7
Bit Name
WEN
6
R/W
5:0
RS[5:0]
Description
Write enable bit. A 0 must be written to this bit so that the write to the communications register actually occurs. If
a 1 is the first bit written, the device does not clock on to subsequent bits in the register. It stays at this bit location
until a 0 is written to this bit. As soon as a 0 is written to the WEN bit, the next seven bits are loaded to the
communications register.
A 0 in this bit location indicates that the next operation is a write to a specified register. A 1 in this position
indicates that the next operation is a read from the designated register.
Register address bits. These address bits select which registers of the ADC are being selected during this serial
interface communication. See Table 63.
STATUS REGISTER
RS[5:0] = 0, 0, 0, 0, 0, 0
Power-On/Reset = 0x00
The status register is an 8-bit, read only register. To access the ADC status register, the user must write to the communications register,
select the next operation to be read, and set the register address bits RS[5:0] to 0.
Table 65 outlines the bit designations for the status register. Bit 7 denotes the first bit of the data stream. The number in parentheses
indicates the power-on/reset default status of that bit.
Bit 7
RDY (0)
Bit 6
ERROR_FLAG (0)
Bit 5
0 (0)
Bit 4
POR_FLAG (0)
Bit 3
Bit 2
Bit 1
CH_ACTIVE (0)
Bit 0
Table 65. Status Register Bit Descriptions
Bits
7
Bit Name
RDY
6
ERROR_FLAG
5
4
0
POR_FLAG
Description
Ready bit for the ADC. This bit is cleared when data is written to the ADC data register. The RDY bit is set
automatically after the ADC data register is read or a period of time before the data register is updated with a
new conversion result to indicate to the user not to read the conversion data. It is also set when the device is
placed in power-down or standby mode. The end of a conversion is also indicated by the DOUT/RDY pin. This
pin can be used as an alternative to the status register for monitoring the ADC for conversion data.
ADC error bit. This bit indicates if one of the error bits has been asserted in the error register. This bit is high if
one or more of the error bits in the error register has been set. This bit is cleared by a read of the error register.
This bit is set to 0.
Power-on reset flag. This bit indicates when a power-on reset occurs. A power-on reset occurs on power-up,
when the power supply voltage goes below a threshold voltage, when a reset is performed, and when coming
out of power-down mode. The status register must be read to clear the bit.
Rev. A | Page 77 of 90
AD7124-4
Bits
3:0
Data Sheet
Bit Name
CH_ACTIVE
Description
These bits indicate which channel is being converted by the ADC.
0000 = Channel 0.
0001 = Channel 1.
0010 = Channel 2.
0011 = Channel 3.
0100 = Channel 4.
0101 = Channel 5.
0110 = Channel 6.
0111 = Channel 7.
1000 = Channel 8.
1001 = Channel 9.
1010 = Channel 10.
1011 = Channel 11.
1100 = Channel 12.
1101 = Channel 13.
1110 = Channel 14.
1111 = Channel 15.
ADC_CONTROL REGISTER
RS[5:0] = 0, 0, 0, 0, 0, 1
Power-On/Reset = 0x0000
Table 66 outlines the bit designations for the register. Bit 15 is the first bit of the data stream. The number in parentheses indicates the
power-on/reset default status of that bit.
Bit 7
0 (0)
Bit 6
0 (0)
Bit 5
0 (0)
Bit 4
DOUT_RDY_DEL (0)
POWER_MODE (0)
Bit 3
CONT_READ (0)
Mode (0)
Bit 2
DATA_STATUS (0)
Bit 1
CS_EN (0)
Bit 0
REF_EN (0)
CLK_SEL (0)
Table 66. ADC Control Register Bit Descriptions
Bits
15:13
12
Bit Name
0
DOUT_RDY_DEL
Description
These bits must be programmed with a Logic 0 for correct operation.
Controls the SCLK inactive edge to DOUT/RDY high time. When DOUT_RDY_DEL is cleared, the delay is
10 ns minimum. When DOUT_RDY_DEL is set, the delay is increased to 100 ns minimum. This function is
useful when CS is tied low (the CS_EN bit is set to 0).
11
CONT_READ
10
DATA_STATUS
9
CS_EN
Continuous read of the data register. When this bit is set to 1 (and the data register is selected), the serial
interface is configured so that the data register can be continuously read; that is, the contents of the data
register are automatically placed on the DOUT pin when the SCLK pulses are applied after the RDY pin
goes low to indicate that a conversion is complete. The communications register does not have to be
written to for subsequent data reads. To enable continuous read, the CONT_READ bit is set. To disable
continuous read, write a read data command while the DOUT/ RDY pin is low. While continuous read is
enabled, the ADC monitors activity on the DIN line so that it can receive the instruction to disable
continuous read. Additionally, a reset occurs if 64 consecutive 1s occur on DIN; therefore, hold DIN low
until an instruction is written to the device.
This bit enables the transmission of the status register contents after each data register read. When
DATA_STATUS is set, the contents of the status register are transmitted along with each data register
read. This function is useful when several channels are selected because the status register identifies the
channel to which the data register value corresponds.
This bit controls when the DOUT/RDY pin transitions from being a DOUT pin to a RDY pin during data
read operations.
When CS_EN is cleared, the DOUT pin returns to being a RDY pin within nanoseconds of the SCLK
inactive edge (the delay is determined by the DOUT_RDY_DEL bit).
When set, the DOUT/RDY pin continues to operate as a DOUT pin after the SCLK inactive edge. The pin
changes function to a RDY pin when CS is taken high. CS_EN must be set to use the diagnostic functions
SPI_WRITE_ERR, SPI_READ_ERR, and SPI_SCLK_CNT_ERR.
Rev. A | Page 78 of 90
Data Sheet
Bits
8
Bit Name
REF_EN
7:6
POWER_MODE
5:2
1:0
Mode
CLK_SEL
AD7124-4
Description
Internal reference voltage enable. When this bit is set, the internal reference is enabled and available at
the REFOUT pin. When this bit is cleared, the internal reference is disabled.
Power Mode Select. These bits select the power mode. The current consumption and output data rate
ranges are dependent on the power mode.
00 = low power.
01 = mid power.
10 = full power.
11 = full power.
These bits control the mode of operation for ADC. See Table 67.
These bits select the clock source for the ADC. Either the on-chip 614.4 kHz clock can be used or an
external clock can be used. The ability to use an external clock allows several AD7124-4 devices to be
synchronized. Also, 50 Hz and 60 Hz rejection is improved when an accurate external clock drives the ADC.
00 = internal 614.4 kHz clock. The internal clock is not available at the CLK pin.
01 = internal 614.4 kHz clock. This clock is available at the CLK pin.
10 = external 614.4 kHz clock.
11 = external clock. The external clock is divided by 4 within the AD7124-4.
Table 67. Operating Modes
Mode
Value
0000
0001
0010
0011
0100
0101
0110
Description
Continuous conversion mode (default). In continuous conversion mode, the ADC continuously performs conversions and places
the result in the data register. RDY goes low when a conversion is complete. The user can read these conversions by placing the device
in continuous read mode whereby the conversions are automatically placed on the DOUT line when SCLK pulses are applied.
Alternatively, the user can instruct the ADC to output the conversion by writing to the communications register. After power-on,
a reset, or a reconfiguration of the ADC, the complete settling time of the filter is required to generate the first valid conversion.
Subsequent conversions are available at the selected output data rate, which is dependent on filter choice.
Single conversion mode. When single conversion mode is selected, the ADC powers up and performs a single conversion on the
selected channel. The conversion requires the complete settling time of the filter. The conversion result is placed in the data
register, RDY goes low, and the ADC returns to standby mode. The conversion remains in the data register and RDY remains
active (low) until the data is read or another conversion is performed.
Standby mode. In standby mode, all sections of the AD7124-4 can be powered down except the LDOs. The internal reference, onchip oscillator, low-side power switch, and bias voltage generator can be enabled or disabled while in standby mode. The onchip registers retain their contents in standby mode.
Any enabled diagnostics remain active when the ADC is in idle mode. The diagnostics can be enabled/disabled while in standby
mode. However, any diagnostics that require the master clock (reference detect, undervoltage/overvoltage detection, LDO trip
tests, memory map CRC, and MCLK counter) must be enabled when the ADC is in continuous conversion mode or idle mode;
these diagnostics do not function if enabled in standby mode.
Power-down mode. In power-down mode, all the AD7124-4 circuitry is powered down, including the current sources, power
switch, burnout currents, bias voltage generator, and clock circuitry. The LDOs are also powered down. In power-down mode, the
on-chip registers do not retain their contents. Therefore, coming out of power-down mode, all registers must be reprogrammed.
Idle mode. In idle mode, the ADC filter and modulator are held in a reset state even though the modulator clocks continue to be
provided.
Internal zero-scale (offset) calibration. An internal short is automatically connected to the input. RDY goes high when the
calibration is initiated and returns low when the calibration is complete. The ADC is placed in idle mode following a calibration.
The measured offset coefficient is placed in the offset register of the selected channel. Select only one channel when zero-scale
calibration is being performed. An internal zero-scale calibration takes a time of one settling period to be performed.
Internal full-scale (gain) calibration. A full-scale input voltage is automatically connected to the selected analog input for this
calibration. RDY goes high when the calibration is initiated and returns low when the calibration is complete. The ADC is placed
in idle mode following a calibration. The measured full-scale coefficient is placed in the gain register of the selected channel. A
full-scale calibration is required each time the gain of a channel is changed to minimize the full-scale error. Select only one
channel when full-scale calibration is being performed. An internal full-scale calibration takes a time of four settling periods for
gains greater than 1. Internal full-scale calibrations cannot be performed at a gain of 1.
Internal full-scale calibrations cannot be performed in the full power mode. So, if using the full-power mode, select mid or low
power mode for the internal full-scale calibration. This calibration is valid in full power mode as the same reference and gain are
used. When performing internal zero-scale and internal full-scale calibrations, the internal full-scale calibration must be
performed before the internal zero-scale calibration. Therefore, write 0x800000 to the offset register before performing any
internal full-scale calibration, which resets the offset register to its default value.
Rev. A | Page 79 of 90
AD7124-4
Mode
Value
0111
1000
1001
to1111
Data Sheet
Description
System zero-scale (offset) calibration. Connect the system zero-scale input to the channel input pins of the selected channel. RDY
goes high when the calibration is initiated and returns low when the calibration is complete. The ADC is placed in idle mode
following a calibration. The measured offset coefficient is placed in the offset register of the selected channel. A system zeroscale calibration is required each time the gain of a channel is changed. Select only one channel when full-scale calibration is
being performed. A system zero-scale calibration takes a time of one settling period to be performed.
System full-scale (gain) calibration. Connect the system full-scale input to the channel input pins of the selected channel. RDY goes
high when the calibration is initiated and returns low when the calibration is complete. The ADC is placed in idle mode following
a calibration. The measured full-scale coefficient is placed in the gain register of the selected channel. A full-scale calibration is
required each time the gain of a channel is changed. Select only one channel when full-scale calibration is being performed. A
system full-scale calibration takes a time of one settling period to be performed.
Reserved.
DATA REGISTER
RS[5:0] = 0, 0, 0, 0, 1, 0
Power-On/Reset = 0x000000
The conversion result from the ADC is stored in this data register. This is a read-only register. On completion of a read operation from
this register, the RDY bit/pin is set.
IO_CONTROL_1 REGISTER
RS[5:0] = 0, 0, 0, 0, 1, 1
Power-On/Reset = 0x000000
Table 68 outlines the bit designations for the register. Bit 23 is the first bit of the data stream. The number in parentheses indicates the
power-on/reset default status of that bit.
Bit 7
GPIO_DAT2 (0)
PDSW (0)
Bit 6
Bit 5
GPIO_DAT1 (0) 0 (0)
0 (0)
IOUT1_CH (0)
Bit 4
0 (0)
IOUT1 (0)
Bit 3
GPIO_CTRL2 (0)
Bit 2
GPIO_CTRL1 (0)
Bit 1
0 (0)
IOUT0 (0)
IOUT0_CH (0)
Bit 0
0 (0)
Table 68. IO_CONTROL_1 Register Bit Descriptions
Bits
23
Bit Name
GPIO_DAT2
22
GPIO_DAT1
21, 20
19
0
GPIO_CTRL2
18
GPIO_CTRL1
17, 16
15
0
PDSW
14
0
Description
Digital Output P2. When GPIO_CTRL2 is set, the GPIO_DAT2 bit sets the value of the P2 general-purpose
output pin. When GPIO_DAT2 is high, the P2 output pin is high. When GPIO_DAT2 is low, the P2 output
pin is low. When the IO_CONTROL_1 register is read, the GPIO_DAT2 bit reflects the status of the P2 pin if
GPIO_CTRL2 is set.
Digital Output P1. When GPIO_CTRL1 is set, the GPIO_DAT1 bit sets the value of the P1 general-purpose
output pin. When GPIO_DAT1 is high, the P1 output pin is high. When GPIO_DAT1 is low, the P1 output
pin is low. When the IO_CONTROL_1 register is read, the GPIO_DAT1 bit reflects the status of the P1 pin if
GPIO_CTRL1 is set.
This bit must be programmed with a Logic 0 for correct operation.
Digital Output P2 enable. When GPIO_CTRL2 is set, the digital output P2 is active. When GPIO_CTRL2 is
cleared, the pin functions as an analog input, AIN3.
Digital Output P1 enable. When GPIO_CTRL1 is set, the digital output P1 is active. When GPIO_CTRL1 is
cleared, the pin functions as an analog input, AIN2.
This bit must be programmed with a Logic 0 for correct operation.
Bridge power-down switch control bit. Set this bit to close the bridge power-down switch PDSW to
AGND. The switch can sink up to 30 mA. Clear this bit to open the bridge power-down switch. When the
ADC is placed in standby mode, the bridge power-down switch remains active.
This bit must be programmed with a Logic 0 for correct operation.
Rev. A | Page 80 of 90
Data Sheet
Bits
13:11
Bit Name
IOUT1
10:8
IOUT0
7:4
IOUT1_CH
3:0
IOUT0_CH
AD7124-4
Description
These bits set the value of the excitation current for IOUT1.
000 = off.
001 = 50 µA.
010 = 100 µA
011 = 250 µA.
100 = 500 µA.
101 = 750 µA.
110 = 1000 µA
111 = 1000 µA.
These bits set the value of the excitation current for IOUT0.
000 = off.
001 = 50 µA.
010 = 100 µA
011 = 250 µA.
100 = 500 µA.
101 = 750 µA.
110 = 1000 µA
111 = 1000 µA.
Channel select bits for the excitation current for IOUT1.
0000 = IOUT1 is available on the AIN0 pin.
0001 = IOUT1 is available on the AIN1 pin.
0010 = reserved
0011 = reserved
0100 = IOUT1 is available on the AIN2 pin.
0101 = IOUT1 is available on the AIN3 pin.
0110 = reserved
0111 = reserved
1000 = reserved
1001 = reserved
1010 = IOUT1 is available on the AIN4 pin.
1011 = IOUT1 is available on the AIN5 pin.
1100 = reserved
1101 = reserved
1110 = IOUT1 is available on the AIN6 pin.
0111 = IOUT1 is available on the AIN7 pin.
Channel select bits for the excitation current for IOUT0.
0000 = IOUT0 is available on the AIN0 pin.
0001 = IOUT0 is available on the AIN1 pin.
0010 = reserved
0011 = reserved
0100 = IOUT0 is available on the AIN2 pin.
0101 = IOUT0 is available on the AIN3 pin.
0110 = reserved
0111 = reserved
1000 = reserved
1001 = reserved
1010 = IOUT0 is available on the AIN4 pin.
1011 = IOUT0 is available on the AIN5 pin.
1100 = reserved
1101 = reserved
1110 = IOUT0 is available on the AIN6 pin.
1111 = IOUT0 is available on the AIN7 pin.
Rev. A | Page 81 of 90
AD7124-4
Data Sheet
IO_CONTROL_2 REGISTER
RS[5:0] = 0, 0, 0, 1, 0, 0
Power-On/Reset = 0x0000
Table 69 outlines the bit designations for the register. Bit 15 is the first bit of the data stream. The number in parentheses indicates the
power-on/reset default status of that bit. The internal bias voltage can be enabled on multiple channels.
Bit 7
VBIAS7 (0)
0 (0)
Bit 6
VBIAS6 (0)
0 (0)
Bit 5
0 (0)
VBIAS3 (0)
Bit 4
0 (0)
VBIAS2 (0)
Bit 3
VBIAS5 (0)
0 (0)
Bit 2
VBIAS4 (0)
0 (0)
Bit 1
0 (0)
VBIAS1 (0)
Bit 0
0 (0)
VBIAS0 (0)
Table 69. IO_CONTROL_2 Register Bit Descriptions
Bits
15
14
13, 12
11
10
9, 8, 7, 6
5
4
3, 2
1
0
Bit Name
VBIAS7
VBIAS6
0
VBIAS5
VBIAS4
0
VBIAS3
VBIAS2
0
VBIAS1
VBIAS0
Description
Enable the bias voltage on the AIN7 channel. When set, the internal bias voltage is available on AIN7.
Enable the bias voltage on the AIN6 channel. When set, the internal bias voltage is available on AIN6.
This bit must be programmed with a Logic 0 for correct operation.
Enable the bias voltage on the AIN5 channel. When set, the internal bias voltage is available on AIN5.
Enable the bias voltage on the AIN4 channel. When set, the internal bias voltage is available on AIN4.
This bit must be programmed with a Logic 0 for correct operation.
Enable the bias voltage on the AIN3 channel. When set, the internal bias voltage is available on AIN3.
Enable the bias voltage on the AIN2 channel. When set, the internal bias voltage is available on AIN2.
This bit must be programmed with a Logic 0 for correct operation.
Enable the bias voltage on the AIN1 channel. When set, the internal bias voltage is available on AIN1.
Enable the bias voltage on the AIN0 channel. When set, the internal bias voltage is available on AIN0.
ID REGISTER
RS[5:0] = 0, 0, 0, 1, 0, 1
Power-On/Reset = 0x02
The identification number for the AD7124-4 is stored in the ID register. This is a read only register.
ERROR REGISTER
RS[5:0] = 0, 0, 0, 1, 1, 0
Power-On/Reset = 0x000000
Diagnostics, such as checking overvoltages and checking the SPI interface, are included on the AD7124-4. The error register contains the
flags for the different diagnostic functions. The functions are enabled and disabled using the ERROR_EN register.
Table 70 outlines the bit designations for the register. Bit 23 is the first bit of the data stream. The number in parentheses indicates the
power-on/reset default status of that bit.
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
AINM_UV_ERR
(0)
SPI_READ_ERR
(0)
LDO_CAP_ERR
(0)
REF_DET_ERR
(0)
SPI_WRITE_ERR
(0)
ADC_CAL_ERR
(0)
0 (0)
ADC_CONV_ERR
(0)
DLDO_PSM_ERR
(0)
MM_CRC_ERR
(0)
ADC_SAT_ERR
(0)
0 (0)
0 (0)
AINP_OV_ERR
(0)
ALDO_PSM_ERR
(0)
AINP_UV_ERR (0)
AINM_OV_ERR (0)
SPI_IGNORE_ERR
(0)
SPI_SCLK_CNT_ERR
(0)
Rev. A | Page 82 of 90
SPI_CRC_ERR
(0)
0 (0)
Data Sheet
AD7124-4
Table 70. Error Register Bit Descriptions
Bits
23:20
19
Bit Name
0
LDO_CAP_ERR
18
ADC_CAL_ERR
17
16
15
14
13
12
11
ADC_CONV_ERR
ADC_SAT_ERR
AINP_OV_ERR
AINP_UV_ERR
AINM_OV_ERR
AINM_UV_ERR
REF_DET_ERR
10
9
8
7
6
0
DLDO_PSM_ERR
0
ALDO_PSM_ERR
SPI_IGNORE_ERR
5
SPI_SCLK_CNT_ERR
4
3
2
1
SPI_READ_ERR
SPI_WRITE_ERR
SPI_CRC_ERR
MM_CRC_ERR
0
0
Description
These bits must be programmed with a Logic 0 for correct operation.
Analog/digital LDO decoupling capacitor check. This flag is set if the decoupling capacitors required for the
analog and digital LDOs are not connected to the AD7124-4.
Calibration check. If a calibration is initiated but not completed, this flag is set to indicate that an error
occurred during the calibration. The associated calibration register is not updated.
This bit indicates whether a conversion is valid. This flag is set if an error occurs during a conversion.
ADC saturation flag. This flag is set if the modulator is saturated during a conversion.
Overvoltage detection on AINP.
Undervoltage detection on AINP.
Overvoltage detection on AINM.
Undervoltage detection on AINM.
Reference detection. This flag indicates when the external reference being used by the ADC is open circuit or
less than 0.7 V.
This bit must be programmed with a Logic 0 for correct operation.
Digital LDO error. This flag is set if an error is detected with the digital LDO.
This bit must be programmed with a Logic 0 for correct operation.
Analog LDO error. This flag is set if an error is detected with the analog LDO voltage.
When a CRC check of the internal registers is being performed, the on-chip registers cannot be accessed.
User instructions are ignored by the ADC. This bit is set when the CRC check of the registers is occurring. The
bit is cleared when the check is complete; read and write operations can only be performed then.
All serial communications are some multiple of eight bits. This bit is set when the number of SCLK cycles is
not a multiple of eight.
This bit is set when an error occurs during an SPI read operation.
This bit is set when an error occurs during an SPI write operation.
This bit is set if an error occurs in the CRC check of the serial communications.
Memory map error. A CRC calculation is performed on the memory map each time that the registers are
written to. Following this, periodic CRC checks are performed on the on-chip registers. If the register
contents have changed, the MM_CRC bit is set.
This bit must be programmed with a Logic 0 for correct operation.
ERROR_EN REGISTER
RS[5:0] = 0, 0, 0, 1, 1, 1
Power-On/Reset = 0x000040
All the diagnostic functions can be enabled or disabled by setting the appropriate bits in this register.
Table 71 outlines the bit designations for the register. Bit 23 is the first bit of the data stream. The number in parentheses indicates the
power-on/reset default status of that bit.
Bit 7
0 (0)
AINP_OV_
ERR_EN (0)
Bit 6
MCLK_CNT_
EN (0)
AINP_UV_
ERR_EN (0)
Bit 5
LDO_CAP_CHK_TEST_EN
(0)
AINM_OV_ERR_
EN (0)
Bit 4
Bit 3
LDO_CAP_CHK (0)
AINM_UV_
ERR_EN (0)
REF_DET_ERR_
EN (0)
ALDO_PSM_
ERR_EN (0)
SPI_IGNORE_
ERR_EN (0)
SPI_SCLK_CNT_
ERR_EN (0)
SPI_READ_
ERR_EN (0)
SPI_WRITE_
ERR_EN (0)
Bit 2
ADC_CAL_ERR_
EN (0)
DLDO_PSM_
TRIP_TEST_EN
(0)
SPI_CRC_ERR_
EN (0)
Bit 1
ADC_CONV_ERR_
EN (0)
DLDO_PSM_ERR_
EN (0)
MM_CRC_ERR_
EN (0)
Bit 0
ADC_SAT_
ERR_EN (0)
ALDO_PSM_
TRIP_TEST_EN
(0)
0 (0)
Table 71. ERROR_EN Register Bit Descriptions
Bits
23
22
Bit Name
0
MCLK_CNT_EN
Description
This bit must be programmed with a Logic 0 for correct operation.
Master clock counter. When this bit is set, the master clock counter is enabled and the result is
reported via the MCLK_COUNT register. The counter monitors the master clock being used by the
ADC. If an external clock is the clock source, the MCLK counter monitors this external clock.
Similarly, if the on-chip oscillator is selected as the clock source to the ADC, the MCLK counter
monitors the on-chip oscillator.
Rev. A | Page 83 of 90
AD7124-4
Bits
21
Bit Name
LDO_CAP_CHK_TEST_EN
20:19
LDO_CAP_CHK
18
17
ADC_CAL_ERR_EN
ADC_CONV_ERR_EN
16
15
14
13
12
11
ADC_SAT_ERR_EN
AINP_OV_ERR_EN
AINP_UV_ERR_EN
AINM_OV_ERR_EN
AINM_UV_ERR_EN
REF_DET_ERR_EN
10
DLDO_PSM_TRIP_TEST_EN
9
DLDO_PSM_ERR_ERR
8
ALDO_PSM_TRIP_TEST_EN
7
ALDO_PSM_ERR_EN
6
SPI_IGNORE_ERR_EN
5
SPI_SCLK_CNT_ERR_EN
4
SPI_READ_ERR_EN
3
SPI_WRITE_ERR_EN
2
SPI_CRC_ERR_EN
1
MM_CRC_ERR_EN
0
0
Data Sheet
Description
Test of analog/digital LDO decoupling capacitor check. When this bit is set, the decoupling
capacitor is internally disconnected from the LDO, forcing a fault condition. This allows the user to
test the circuitry which is used for the analog and digital LDO decoupling capacitor check.
Analog/digital LDO decoupling capacitor check. These bits enable the capacitor check. When a
check is enabled, the ADC checks for the presence of the external decoupling capacitor on the
selected supply. When the check is complete, the LDO_CAP_CHK bits are both reset to 0.
00 = check is not enabled.
01 = check the analog LDO capacitor.
10 = check the digital LDO capacitor.
11 = check is not enabled.
When this bit is set, the calibration fail check is enabled.
When this bit is set, the conversions are monitored and the ADC_CONV_ERR bit is set when a
conversion fails.
When this bit is set, the ADC modulator saturation check is enabled.
When this bit is set, the overvoltage monitor on all enabled AINP channels is enabled.
When this bit is set, the undervoltage monitor on all enabled AINP channels is enabled.
When this bit is set, the overvoltage monitor on all enabled AINM channels is enabled.
When this bit is set, the undervoltage monitor on all enabled AINM channels is enabled.
When this bit is set, any external reference being used by the ADC is continuously monitored. An
error is flagged if the external reference is open circuit or has a value of less than 0.7 V.
Checks the test mechanism that monitors the digital LDO. When this bit is set, the input to the test
circuit is tied to DGND instead of the LDO output. Set the DLDO_PSM_ERR bit in the error register.
When this bit is set, the digital LDO voltage is continuously monitored. The DLDO_PSM_ERR bit in
the error register is set if the voltage being output from the digital LDO is outside specification.
Checks the test mechanism that monitors the analog LDO. When this bit is set, the input to the
test circuit is tied to AVSS instead of the LDO output. Set the ALDO_PSM_ERR bit in the error
register.
When this bit is set, the analog LDO voltage is continuously monitored. The ALDO_PSM_ERR bit in
the error register is set if the voltage being output from the analog LDO is outside specification.
When a CRC check of the internal registers is being performed, the on-chip registers cannot be
accessed. User instructions are ignored by the ADC. Set this bit so that the SPI_IGNORE_ERR bit in
the error register informs the user when read and write operations must not be performed.
When this bit is set, the SCLK counter is enabled. All read and write operations to the ADC are
multiples of eight bits. For every serial communication, the SCLK counter counts the number of
SCLK pulses. CS must be used to frame each read and write operation. If the number of SCLK
pulses used during a communication is not a multiple of eight, the SPI_SCLK_CNT_ERR bit in the
error register is set. For example, a glitch on the SCLK pin during a read or write operation can be
interpreted as an SCLK pulse. In this case, the SPI_SCLK_CNT_ERR bit is set as there is an excessive
number of SCLK pulses detected. CS_EN in the ADC_CONTROL register must be set to 1 when the
SCLK counter function is being used.
When this bit is set, the SPI_READ_ERR bit in the error register is set when an error occurs during a
read operation. An error occurs if the user attempts to read from invalid addresses.
CS_EN in the ADC_CONTROL register must be set to 1 when the SPI read check function is being
used.
When this bit is set, the SPI_WRITE_ERR bit in the error register is set when an error occurs during a
write operation. An error occurs if the user attempts to write to invalid addresses or write to readonly registers. CS_EN in the ADC_CONTROL register must be set to 1 when the SPI write check
function is being used.
This bit enables a CRC check of all read and write operations. The SPI_CRC_ERR bit in the error
register is set if the CRC check fails. In addition, an 8-bit CRC word is appended to all data read
from the AD7124-4.
When this bit is set, a CRC calculation is performed on the memory map each time that the
registers are written to. Following this, periodic CRC checks are performed on the on-chip
registers. If the register contents have changed, the MM_CRC bit is set.
This bit must be programmed with a Logic 0 for correct operation.
Rev. A | Page 84 of 90
Data Sheet
AD7124-4
MCLK_COUNT REGISTER
RS[5:0] = 0, 0, 1, 0, 0, 0
Power-On/Reset = 0x00
The master clock frequency can be monitored using this register.
Table 72 outlines the bit designations for the register. Bit 7 is the first bit of the data stream. The number in parentheses indicates the
power-on/reset default status of that bit.
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
MCLK_COUNT (0)
Bit 2
Bit 1
Bit 0
Table 72. MCLK_COUNT Register Bit Descriptions
Bits
7:0
Bit Name
MCLK_COUNT
Description
This register allows the user to determine the frequency of the internal/external oscillator. Internally, a clock
counter increments every 131 pulses of the sampling clock (614.4 kHz in full power mode, 153.6 kHz in mid power
mode, and 768 kHz in low power mode). The 8-bit counter wraps around on reaching its maximum value. The
counter output is read back via this register.
CHANNEL REGISTERS
RS[5:0] = 0, 0, 1, 0, 0, 1 to 0, 1, 1, 0, 0, 0
Power-On/Reset = 0x8001 for CHANNEL_0; all other channel registers are set to 0x0001
Sixteen channel registers are included on the AD7124-4, CHANNEL_0 to CHANNEL_15. The channel registers begin at Address 0x09
(CHANNEL_0) and end at Address 0x18 (CHANNEL_15). Via each register, the user can configure the channel (AINP input and AINM
input), enable or disable the channel, and select the setup. The setup is selectable from eight different options defined by the user. When
the ADC converts, it automatically sequences through all enabled channels. This allows the user to sample some channels multiple times
in a sequence, if required. In addition, it allows the user to include diagnostic functions in a sequence also.
Table 73 outlines the bit designations for the register. Bit 15 is the first bit of the data stream. The number in parentheses indicates the
power-on/reset default status of that bit.
Bit 7
Enable (1)
Bit 6
Bit 5
Bit 4
Bit 3
Setup (0)
AINP[2:0](000)
Bit 2
0 (0)
AINM[4:0](00001)
Bit 1
Bit 0
AINP[4:3](00)
Table 73. Channel Register Bit Descriptions
Bits
15
Bit Name
Enable
14:12
Setup
11:10
9:5
0
AINP[4:0]
Description
Channel enable bit. Setting this bit enables the device channel for the conversion sequence. By default, only the
enable bit for Channel 0 is set. The order of conversions starts with the lowest enabled channel, then cycles
through successively higher channel numbers, before wrapping around to the lowest channel again.
When the ADC writes a result for a particular channel, the four LSBs of the status register are set to the channel
number, 0 to 15. This allows the channel the data corresponds to be identified. When the DATA_STATUS bit in the
ADC_CONTROL register is set, the contents of the status register are appended to each conversion when it is
read. Use this function when several channels are enabled to determine to which channel the conversion value
read corresponds.
Setup select. These bits identify which of the eight setups are used to configure the ADC for this channel. A setup
comprises a set of four registers: analog configuration, output data rate/filter selection, offset register, and gain
register. All channels can use the same setup, in which case the same 3-bit value must be written to these bits on
all active channels. Alternatively, up to eight channels can be configured differently.
These bits must be programmed with a Logic 0 for correct operation.
Positive analog input AINP input select. These bits select which of the analog inputs is connected to the positive
input for this channel.
00000 = AIN0 (default).
00001 = AIN1.
00010 = AIN2.
00011 = AIN3.
00100 = AIN4.
000101 = AIN5.
Rev. A | Page 85 of 90
AD7124-4
Bits
Bit Name
4:0
AINM[4:0]
Data Sheet
Description
00110 = AIN6.
00111 = AIN7.
01000 to 01111 = reserved.
10000 = temperature sensor.
10001 = AVSS.
10010 = internal reference.
10011 = DGND.
10100 = (AVDD − AVSS)/6+. Use in conjunction with (AVDD − AVSS)/6− to monitor supply AVDD − AVSS.
10101 = (AVDD − AVSS)/6−. Use in conjunction with (AVDD − AVSS)/6+ to monitor supply AVDD − AVSS.
10110 = (IOVDD − DGND)/6+. Use in conjunction with (IOVDD − DGND)/6− to monitor IOVDD − DGND.
10111 = (IOVDD − DGND)/6−. Use in conjunction with (IOVDD − DGND)/6+ to monitor IOVDD − DGND.
11000 = (ALDO − AVSS)/6+. Use in conjunction with (ALDO − AVSS)/6− to monitor the analog LDO.
11001 = (ALDO − AVSS)/6−. Use in conjunction with (ALDO − AVSS)/6+ to monitor the analog LDO.
11010 = (DLDO − DGND)/6+. Use in conjunction with (DLDO − DGND)/6− to monitor the digital LDO.
11011 = (DLDO − DGND)/6−. Use in conjunction with (DLDO − DGND)/6+ to monitor the digital LDO.
11100 = V_20MV_P. Use in conjunction with V_20MV_M to apply a 20 mV p-p signal to the ADC.
11101 = V_20MV_M. Use in conjunction with V_20MV_P to apply a 20 mV p-p signal to the ADC.
10010 = REFOUT.
10011 = DGND.
Negative analog input AINM input select. These bits select which of the analog inputs is connected to the
negative input for this channel.
00000 = AIN0 (default).
00001 = AIN1.
00010 = AIN2.
00011 = AIN3.
00100 = AIN4.
000101 = AIN5.
00110 = AIN6.
00111 = AIN7.
01000 to 01111 = reserved.
10000 = temperature sensor.
10001 = AVSS.
10010 = internal reference.
10011 = DGND.
10100 = (AVDD − AVSS)/6+. Use in conjunction with (AVDD − AVSS)/6− to monitor supply AVDD − AVSS.
10101 = (AVDD − AVSS)/6−. Use in conjunction with (AVDD − AVSS)/6+ to monitor supply AVDD − AVSS.
10110 = (IOVDD − DGND)/6+. Use in conjunction with (IOVDD − DGND)/6− to monitor IOVDD − DGND.
10111 = (IOVDD − DGND)/6−. Use in conjunction with (IOVDD − DGND)/6+ to monitor IOVDD − DGND.
11000 = (ALDO − AVSS)/6+. Use in conjunction with (ALDO − AVSS)/6− to monitor the analog LDO.
11001 = (ALDO − AVSS)/6−. Use in conjunction with (ALDO − AVSS)/6+ to monitor the analog LDO.
11010 = (DLDO − DGND)/6+. Use in conjunction with (DLDO − DGND)/6− to monitor the digital LDO.
11011 = (DLDO − DGND)/6−. Use in conjunction with (DLDO − DGND)/6+ to monitor the digital LDO.
11100 = V_20MV_P. Use in conjunction with V_20MV_M to apply a 20 mV p-p signal to the ADC.
11101 = V_20MV_M. Use in conjunction with V_20MV_P to apply a 20 mV p-p signal to the ADC.
11110 = reserved.
11111 = reserved.
Rev. A | Page 86 of 90
Data Sheet
AD7124-4
CONFIGURATION REGISTERS
RS[5:0] = 0, 1, 1, 0, 0, 1 to 1, 0, 0, 0, 0, 0
Power-On/Reset = 0x0860
The AD7124-4 has eight configuration registers, CONFIG_0 to CONFIG_7. Each configuration register is associated with a setup;
CONFIG_x is associated with Setup x. In the configuration register, the reference source, polarity, reference buffers enabled or disabled
are configured.
Table 74 outlines the bit designations for the register. Bit 15 is the first bit of the data stream. The number in parentheses indicates the
power-on/reset default status of that bit.
Bit 7
Bit 6
REF_BUFM (0)
0 (0)
AIN_BUFP (1)
Bit 5
Bit 4
AIN_BUFM (1)
Bit 3
Bipolar (1)
REF_SEL (0)
Bit 2
Bit 1
Burnout (0)
Bit 0
REF_BUFP (0)
PGA (0)
Table 74. Configuration Register Bit Descriptions
Bits
15:12
11
Bit Name
0
Bipolar
10:9
Burnout
8
REF_BUFP
7
REF_BUFM
6
AIN_BUFP
5
AIN_BUFM
4:3
REF_SEL
2:0
PGA
Description
These bits must be programmed with a Logic 0 for correct operation.
Polarity select bit. When this bit is set, bipolar operation is selected. When this bit is cleared, unipolar operation is
selected.
These bits select the magnitude of the sensor burnout detect current source.
00 = burnout current source off (default).
01 = burnout current source on, 0.5 μA.
10 = burnout current source on, 2 μA.
11 = burnout current source on, 4 μA.
Buffer enable on REFINx(+). When this bit is set, the positive reference input (internal or external) is buffered. When
this bit is cleared, the positive reference input (internal or external) is unbuffered.
Buffer enable on REFINx(−). When this bit is set, the negative reference input (internal or external) is buffered. When
this bit is cleared, the negative reference input (internal or external) is unbuffered.
Buffer enable on AINP. When this bit is set, the selected positive analog input pin is buffered. When this bit is cleared,
the selected positive analog input pin is unbuffered.
Buffer enable on AINM. When this bit is set, the selected negative analog input pin is buffered. When this bit is
cleared, the selected negative analog input pin is unbuffered.
Reference source select bits. These bits select the reference source to use when converting on any channels using
this configuration register.
00 = REFIN1(+)/REFIN1(−).
01 = REFIN2(+)/REFIN2(−).
10 = internal reference.
11 = AVDD.
Gain select bits. These bits select the gain to use when converting on any channels using this configuration register.
PGA
Gain
Input Range When VREF = 2.5 V (Bipolar Mode)
000
1
±2.5 V
001
2
±1.25 V
010
4
± 625 mV
011
8
±312.5 mV
100
16
±156.25 mV
101
32
±78.125 mV
110
64
±39.06 mV
111
128
±19.53 mV
Rev. A | Page 87 of 90
AD7124-4
Data Sheet
FILTER REGISTERS
RS[5:0] = 1, 0, 0, 0, 0, 1 to 1, 0, 1, 0, 0, 0
Power-On/Reset = 0x060180
The AD7124-4 has eight filter registers, FILTER_0 to FILTER_7. Each filter register is associated with a setup; FILTER_x is associated
with Setup x. In the filter register, the filter type and output word rate are set.
Table 75 outlines the bit designations for the register. Bit 15 is the first bit of the data stream. The number in parentheses indicates the
power-on/reset default status of that bit.
Bit 7
Bit 6
Filter (0)
Bit 5
Bit 4
REJ60 (0)
Bit 3
Bit 2
Bit 1
POST_FILTER (0)
0 (0)
Bit 0
SINGLE_CYCLE (0)
FS[10:8] (0)
FS[7:0] (0)
Table 75. Filter Register Bit Descriptions
Bits
23:21
Bit Name
Filter
20
REJ60
19:17
POST_FILTER
16
SINGLE_CYCLE
15:11
10:0
0
FS[10:0]
Description
Filter type select bits. These bits select the filter type.
000 = sinc4 filter (default).
001 = reserved.
010 = sinc3 filter.
011 = reserved.
100 = fast settling filter using the sinc4 filter. The sinc4 filter is followed by an averaging block, which results
in a settling time equal to the conversion time. In full power and mid power modes, averaging by 16 occurs
whereas averaging by 8 occurs in low power mode.
101 = fast settling filter using the sinc3 filter. The sinc3 filter is followed by an averaging block, which results
in a settling time equal to the conversion time. In full power and mid power modes, averaging by 16 occurs
whereas averaging by 8 occurs in low power mode.
110 = reserved.
111 = post filter enabled. The AD7124-4 includes several post filters, selectable using the POST_FILTER bits.
The post filters have single cycle settling, the settling time being considerably better than a simple
sinc3/sinc4 filter. These filters offer excellent 50 Hz and60 Hz rejection.
When this bit is set, a first order notch is placed at 60 Hz when the first notch of the sinc filter is at 50 Hz.
This allows simultaneous 50 Hz and 60 Hz rejection.
Post filter type select bits. When the filter bits are set to 1, the sinc3 filter is followed by a post filter which
offers good 50 Hz and 60 Hz rejection at output data rates that have zero latency approximately.
POST_FILTER
Output Data Rate (SPS)
Rejection at 50 Hz and 60 Hz ± 1 Hz (dB)
000
Reserved
Not applicable
010
Reserved
Not applicable
010
27.27
47
011
25
62
100
Reserved
Not applicable
101
20
86
110
16.7
92
111
Reserved
Not applicable
Single cycle conversion enable bit. When this bit is set, the AD7124-4 settles in one conversion cycle so that
it functions as a zero latency ADC. This bit has no effect when multiple analog input channels are enabled
or when the single conversion mode is selected. When the fast filters are used, this bit has no effect.
These bits must be programmed with a Logic 0 for correct operation.
Filter output data rate select bits. These bits set the output data rate of the sinc3 and sinc4 filters as well as
the fast settling filters. In addition, they affect the position of the first notch of the filter and the cutoff
frequency. In association with the gain selection, they also determine the output noise and, therefore, the
effective resolution of the device (see noise tables). FS can have a value from 1 to 2047.
Rev. A | Page 88 of 90
Data Sheet
AD7124-4
OFFSET REGISTERS
GAIN REGISTERS
RS[5:0] = 1, 0, 1, 0, 0, 1 to 1, 1, 0, 0, 0, 0
Power-On/Reset = 0x800000
RS[5:0] = 1, 1, 0, 0, 0, 1 to 1, 1, 1, 0, 0, 0
Power-On/Reset = 0x5XXXXX
The AD7124-4 has eight offset registers, OFFSET_0 to OFFSET_7.
Each offset register is associated with a setup; OFFSET_x is
associated with Setup x. The offset registers are 24-bit registers
and hold the offset calibration coefficient for the ADC and its
power-on reset value is 0x800000. Each of these registers is a
read/write register. These registers are used in conjunction with
the associated gain register to form a register pair. The poweron reset value is automatically overwritten if an internal or
system zero-scale calibration is initiated by the user. The ADC
must be placed in standby mode or idle mode when writing to
the offset registers.
The AD7124-4 has eight gain registers, GAIN_0 to GAIN_7. Each
gain register is associated with a setup; GAIN_x is associated
with Setup x. The gain registers are 24-bit registers and hold the
full-scale calibration coefficient for the ADC. The AD7124-4 is
factory calibrated to a gain of 1. The gain register contains this
factory generated value on power-on and after a reset. The gain
registers are read/write registers. However, when writing to the
registers, the ADC must be placed in standby mode or idle
mode. The default value is automatically overwritten if an
internal or system full-scale calibration is initiated by the user
or the full-scale registers are written to.
Rev. A | Page 89 of 90
AD7124-4
Data Sheet
OUTLINE DIMENSIONS
5.10
5.00 SQ
4.90
PIN 1
INDICATOR
0.30
0.25
0.18
32
25
1
24
0.50
BSC
*3.75
3.60 SQ
3.55
EXPOSED
PAD
17
9
BOTTOM VIEW
FOR PROPER CONNECTION OF
THE EXPOSED PAD, REFER TO
THE PIN CONFIGURATION AND
FUNCTION DESCRIPTIONS
SECTION OF THIS DATA SHEET.
0.05 MAX
0.02 NOM
COPLANARITY
0.08
0.20 REF
SEATING
PLANE
0.25 MIN
08-16-2010-B
0.80
0.75
0.70
8
16
0.50
0.40
0.30
TOP VIEW
PIN 1
INDICATOR
*COMPLIANT TO JEDEC STANDARDS MO-220-WHHD-5
WITH THE EXCEPTION OF THE EXPOSED PAD DIMENSION.
Figure 130. 32-Lead Lead Frame Chip Scale Package [LFCSP_WQ]
5 mm x 5 mm Body, Very, Very Thin Quad
(CP-32-12)
Dimensions shown in millimeters
7.90
7.80
7.70
24
13
4.50
4.40
4.30
6.40 BSC
1
12
PIN 1
0.65
BSC
0.15
0.05
0.30
0.19
1.20
MAX
SEATING
PLANE
0.20
0.09
8°
0°
0.75
0.60
0.45
0.10 COPLANARITY
COMPLIANT TO JEDEC STANDARDS MO-153-AD
Figure 131. 24-Lead Thin Shrink Small Outline Package [TSSOP]
(RU-24)
Dimensions shown in millimeters
ORDERING GUIDE
Model1
AD7124-4BCPZ
AD7124-4BCPZ-RL
AD7124-4BCPZ-RL7
AD7124-4BRUZ
AD7124-4BRUZ-RL
AD7124-4BRUZ-RL7
EVAL-AD7124-4SDZ
EVAL-SDP-CB1Z
1
Temperature Range
−40°C to +105°C
−40°C to +105°C
−40°C to +105°C
−40°C to +105°C
−40°C to +105°C
−40°C to +105°C
Package Description
32-Lead Lead Frame Chip Scale Package [LFCSP_WQ]
32-Lead Lead Frame Chip Scale Package [LFCSP_WQ]
32-Lead Lead Frame Chip Scale Package [LFCSP_WQ]
24-Lead Thin Shrink Small Outline Package [TSSOP]
24-Lead Thin Shrink Small Outline Package [TSSOP]
24-Lead Thin Shrink Small Outline Package [TSSOP]
Evaluation Board
Evaluation Controller Board
Z = RoHS Compliant Part.
©2015 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D13197-0-7/15(A)
Rev. A | Page 90 of 90
Package Option
CP-32-12
CP-32-12
CP-32-12
RU-24
RU-24
RU-24
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