Texas Instruments | 16-Channel, 16-Bit Analog-to-Digital Converter (Rev. D) | Datasheet | Texas Instruments 16-Channel, 16-Bit Analog-to-Digital Converter (Rev. D) Datasheet

Texas Instruments 16-Channel, 16-Bit Analog-to-Digital Converter (Rev. D) Datasheet
ADS1158
AD
S1
158
SBAS429D – JUNE 2008 – REVISED MARCH 2011
www.ti.com
16-Channel, 16-Bit Analog-to-Digital Converter
Check for Samples: ADS1158
FEATURES
DESCRIPTION
•
•
•
•
•
•
•
•
•
The ADS1158 is a 16-channel (multiplexed),
low-noise, 16-bit, delta-sigma (ΔΣ) analog-to-digital
converter (ADC) that provides single-cycle settled
data at channel scan rates from 1.8k to 23.7k
samples per second (SPS) per channel. A flexible
input multiplexer accepts combinations of eight
differential or 16 single-ended inputs with a full-scale
differential range of 5V or true bipolar range of ±2.5V
when operating with a 5V reference. The fourth-order
delta-sigma modulator is followed by a fifth-order sinc
digital filter optimized for low-noise performance.
1
23
•
•
•
•
•
•
•
•
16 Bits, No Missing Codes
Fixed-Channel or Automatic Channel Scan
Fixed-Channel Data Rate: 125kSPS
Auto-Scan Data Rate: 23.7kSPS/Channel
Single-Conversion Settled Data
16 Single-Ended or 8 Differential Inputs
Unipolar (+5V) or Bipolar (±2.5V) Operation
0.3LSB (INL)
DC Stability:
1μV/°C Offset Drift, 2ppm/°C Gain Drift
Open-Sensor Detection
Conversion Control Pin
Multiplexer Output for External Signal
Conditioning
On-Chip Temperature, Reference, Offset, Gain,
and Supply Voltage Readback
42mW Power Dissipation
Standby, Sleep, and Power-Down Modes
Eight General-Purpose Inputs/Outputs (GPIO)
32.768kHz Crystal Oscillator or External Clock
APPLICATIONS
•
•
•
•
•
The differential output of the multiplexer is accessible
to allow signal conditioning before the input of the
ADC. Internal system monitor registers provide
supply voltage, temperature, reference voltage, gain,
and offset data.
An onboard PLL generates the system clock from a
32.768kHz crystal, or can be overridden by an
external clock source. A buffered system clock output
(15.7MHz) is provided to drive a microcontroller or
additional converters.
Serial digital communication is handled via an
SPI™-compatible interface. A simple command word
structure controls channel configuration, data rates,
digital I/O, monitor functions, etc.
Programmable sensor bias current sources can be
used to bias sensors or verify sensor integrity.
Medical, Avionics, and Process Control
Machine and System Monitoring
Fast Scan Multi-Channel Instrumentation
Industrial Systems
Test and Measurement Systems
The ADS1158 operates from a unipolar +5V or
bipolar ±2.5V analog supply and a digital supply
compatible with interfaces ranging from 2.7V to
5.25V. The ADS1158 is available in a QFN-48
package.
AVDD
DVDD
VREF
Internal
Monitoring
GPIO[7:0]
ADS1158
GPIO
Digital
Filter
SPI
Interface
CS
DRDY
SCLK
DIN
DOUT
Oscillator
Control
START
RESET
PWDN
Analog Inputs
¼
1
16-Bit
ADC
16:1
Analog
Input
MUX
16
AINCOM
AVSS
MUX
OUT
ADC
IN
Ext CLK
In/Out
32.768kHz
DGND
1
2
3
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas
Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
SPI is a trademark of Motorola, Inc.
All other trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2008–2011, Texas Instruments Incorporated
ADS1158
SBAS429D – JUNE 2008 – REVISED MARCH 2011
www.ti.com
This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more
susceptible to damage because very small parametric changes could cause the device not to meet its published specifications.
ORDERING INFORMATION
For the most current package and ordering information see the Package Option Addendum at the end of this
document, or see the TI web site at www.ti.com.
ABSOLUTE MAXIMUM RATINGS
Over operating free-air temperature range, unless otherwise noted. (1)
ADS1158
UNIT
AVDD to AVSS
–0.3 to +5.5
V
AVSS to DGND
–2.8 to +0.3
V
DVDD to DGND
–0.3 to +5.5
V
Input current
100, momentary
mA
Input current
10, continuous
mA
AVSS – 0.3 to AVDD + 0.3
V
Analog input voltage
–0.3 to DVDD + 0.3
V
+150
°C
Operating temperature range
–40 to +105
°C
Storage temperature range
–60 to +150
°C
Digital input voltage to DGND
Maximum junction temperature
(1)
2
Stresses above these ratings may cause permanent damage. Exposure to absolute maximum conditions for extended periods may
degrade device reliability. These are stress ratings only, and functional operation of the device at these or any other conditions beyond
those specified is not implied.
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ELECTRICAL CHARACTERISTICS
All specifications at TA = –40°C to +105°C, AVDD = +2.5V, AVSS = –2.5V, DVDD = +3.3V, fCLK = 16MHz (external clock) or fCLK =
15.729MHz (internal clock), OPA227 buffer between MUX outputs and ADC inputs, VREF = +4.096V, and VREFN = –2.5V, unless otherwise
noted.
ADS1158
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNIT
AVDD + 100mV
V
ANALOG MULTIPLEXER INPUTS
Absolute input voltage
AIN0–AIN15,
AINCOM with respect to DGND
AVSS – 100mV
80
Ω
fIN = 1kHz
–110
dB
SBCS[1:0] = 01
1.5
SBCS[1:0] = 11
24
On-channel resistance
Crosstalk
Sensor bias (current source)
1.5μA:24μA ratio error
μA
1
%
ADC INPUT
Full-scale input voltage
(VIN = ADCINP – ADCINN)
Absolute input voltage
(ADCINP, ADCINN)
±1.06 VREF
AVSS – 100mV
Differential input impedance
V
AVDD + 100mV
V
65
kΩ
SYSTEM PERFORMANCE
Resolution
No missing codes
16
Data rate, fixed-channel mode
Data rate, auto-scan mode
125
1.805
Integral nonlinearity (INL) (1)
Offset error
Bits
1.953
Differential input
Chopping on
–1
Shorted inputs
Offset drift
Shorted inputs
kSPS
23.739
kSPS
0.3
1
LSB (2)
–0.5 (3)
0
LSB
μV/°C
1
Gain error
0.1
Gain drift
2
ppm/°C
0.6
LSB (PP)
100
dB
Noise
Common-mode rejection
Power-supply rejection
fCM = 60Hz
AVDD, AVSS
%
85
fPS = 60Hz
DVDD
0.5
dB
95
VOLTAGE REFERENCE INPUT
AVDD – AVSS
V
Negative reference input (VREFN)
AVSS – 0.1V
VREFP – 0.5
V
Positive reference input (VREFP)
VREFN + 0.5
AVDD + 0.1V
Reference input voltage
(VREF = VREFP – VREFN)
0.5
Reference input impedance
4.096
V
40
kΩ
SYSTEM PARAMETERS
External reference reading error
1
3
Analog supply reading error
1
5
Voltage
Temperature sensor reading
(1)
(2)
(3)
(4)
(5)
TA = +25°C
Coefficient
%
%
168
mV
394 (4)
μV/°C
(5)
μV/°C
563
Best straight line fit method.
FSR = Full-scale range = 2.13VREF.
Systematic –0.5LSB in reading code.
ADS1158 temperature forced alone, test PCB in free air.
ADS1158 and test PCB temperatures forced together.
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ELECTRICAL CHARACTERISTICS (continued)
All specifications at TA = –40°C to +105°C, AVDD = +2.5V, AVSS = –2.5V, DVDD = +3.3V, fCLK = 16MHz (external clock) or
fCLK = 15.729MHz (internal clock), OPA227 buffer between MUX outputs and ADC inputs, VREF = +4.096V, and VREFN
= –2.5V, unless otherwise noted.
ADS1158
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNIT
DIGITAL INPUT/OUTPUT
Logic levels
VIH
0.7DVDD
DVDD
V
VIL
DGND
0.3DVDD
V
V
VOH
IOH = 2mA
0.8DVDD
DVDD
VOL
IOL = 2mA
DGND
0.2DVDD
V
10
μA
MHz
Input leakage
Master clock input (CLKIO)
Crystal oscillator
(see Crystal Oscillator section)
VIN = DVDD, GND
Frequency
0.1
16
Duty cycle
40
60
%
Crystal frequency
32.768
kHz
Clock output frequency
15.729
MHz
Start-up time (clock output valid)
150
Clock output duty cycle
ms
40
60
%
DVDD
2.7
5.25
V
AVSS
–2.6
0
V
AVDD
AVSS + 4.75
AVSS + 5.25
V
0.6
mA
POWER SUPPLY
DVDD supply current
AVDD, AVSS supply current
Power dissipation
(6)
(7)
4
External clock
operation
0.25
Internal oscillator
operation, clock
output disabled
0.04
mA
Internal oscillator
operation, clock
output enabled (6)
1.4
mA
Power-down (7)
1
25
µA
Converting
8.2
12
mA
Standby
5.6
Sleep
2.1
Power-down
2
200
µA
Converting
42
62
mW
Standby
29
mW
Sleep
11
mW
Power-down
14
μW
mA
mA
CLKIO load = 20pF.
No clock applied to CLKIO.
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PIN CONFIGURATION
AIN4
AIN5
AIN6
AIN7
MUXOUTP
MUXOUTN
ADCINP
ADCINN
AIN8
AIN9
AIN10
AIN11
QFN PACKAGE
(TOP VIEW)
48
47
46
45
44
43
42
41
40
39
38
37
AIN3
1
36
AIN12
AIN2
2
35
AIN13
AIN1
3
34
AIN14
AIN0
4
33
AIN15
AVSS
5
32
AINCOM
AVDD
6
31
VREFP
ADS1158
PWDN
10
27
CS
RESET
11
26
START
CLKSEL
12
25
DRDY
13
14
15
16
17
18
19
20
21
22
23
24
DOUT
DVDD
DIN
28
SCLK
9
GPIO7
XTAL2
GPIO6
DGND
GPIO5
29
GPIO4
8
GPIO3
XTAL1
GPIO2
VREFN
GPIO1
30
GPIO0
7
CLKIO
PLLCAP
PIN ASSIGNMENTS
PIN #
NAME
ANALOG/DIGITAL
INPUT/OUTPUT
1
AIN3
Analog input
Analog input 3: single-ended channel 3, differential channel 1 (–)
2
AIN2
Analog input
Analog input 2: single-ended channel 2, differential channel 1 (+)
3
AIN1
Analog input
Analog input 1: single-ended channel 1, differential channel 0 (–)
4
AIN0
Analog input
Analog input 0: single-ended channel 0, differential channel 0 (+)
5
AVSS
Analog
Negative analog power supply: 0V for unipolar operation, –2.5V for bipolar operation.
(Internally connected to exposed thermal pad of QFN package.)
6
AVDD
Analog
Positive analog power supply: +5V for unipolar operation, +2.5V for bipolar operation.
7
PLLCAP
Analog
PLL bypass capacitor: connect 22nF capacitor to AVSS when using crystal oscillator.
8
XTAL1
Analog
32.768kHz crystal oscillator input 1; see Crystal Oscillator section.
32.768kHz crystal oscillator input 2; see Crystal Oscillator section.
DESCRIPTION
9
XTAL2
Analog
10
PWDN
Digital input
Power-down input: hold low for minimum of two fCLK cycles to engage low-power mode.
11
RESET
Digital input
Reset input: hold low for minimum of two fCLK cycles to reset the device.
12
CLKSEL
Digital input
Clock select input: Low = activates crystal oscillator, fCLK output on CLKIO.
High = disables crystal oscillator, apply fCLK to CLKIO.
13
CLKIO
Digital I/O
System clock input/output (see CLKSEL pin)
14
GPIO0
Digital I/O
General-purpose digital input/output 0
15
GPIO1
Digital I/O
General-purpose digital input/output 1
16
GPIO2
Digital I/O
General-purpose digital input/output 2
17
GPIO3
Digital I/O
General-purpose digital input/output 3
18
GPIO4
Digital I/O
General-purpose digital input/output 4
19
GPIO5
Digital I/O
General-purpose digital input/output 5
20
GPIO6
Digital I/O
General-purpose digital input/output 6
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PIN ASSIGNMENTS (continued)
6
PIN #
NAME
ANALOG/DIGITAL
INPUT/OUTPUT
21
GPIO7
Digital I/O
22
SCLK
Digital input
SPI interface clock input: data clocked in on rising edge, clocked out on falling edge.
23
DIN
Digital input
SPI interface data input: data are input to the device.
24
DOUT
Digital output
SPI interface data output: data are output from the device.
25
DRDY
Digital output
Data ready output: active low.
26
START
Digital input
Start conversion input: active high.
27
CS
Digital input
SPI interface chip select input: active low.
28
DVDD
Digital
Digital power supply: 2.7V to 5.25V
29
DGND
Digital
Digital ground
30
VREFN
Analog input
Reference input negative
31
VREFP
Analog input
Reference input positive
32
AINCOM
Analog input
Analog input common: common input pin to all single-ended inputs.
33
AIN15
Analog input
Analog input 15: single-ended channel 15, differential channel 7 (–)
34
AIN14
Analog input
Analog input 14: single-ended channel 14, differential channel 7 (+)
35
AIN13
Analog input
Analog input 13: single-ended channel 13, differential channel 6 (–)
36
AIN12
Analog input
Analog input 12: single-ended channel 12, differential channel 6 (+)
37
AIN11
Analog input
Analog input 11: single-ended channel 11, differential channel 5 (–)
38
AIN10
Analog input
Analog input 10: single-ended channel 10, differential channel 5 (+)
39
AIN9
Analog input
Analog input 9: single-ended channel 9, differential channel 4 (–)
40
AIN8
Analog input
Analog input 8: single-ended channel 8, differential channel 4 (+)
41
ADCINN
Analog input
ADC differential input (–)
42
ADCINP
Analog input
ADC differential input (+)
43
MUXOUTN
Analog output
Multiplexer differential output (–)
44
MUXOUTP
Analog output
Multiplexer differential output (+)
45
AIN7
Analog input
Analog input 7: single-ended channel 7, differential channel 3 (–)
46
AIN6
Analog input
Analog input 6 : single-ended channel 6, differential channel 3 (+)
47
AIN5
Analog input
Analog input 5: single-ended channel 5, differential channel 2 (–)
48
AIN4
Analog input
Analog input 4: single-ended channel 4, differential channel 2 (+)
DESCRIPTION
General-purpose digital input/output 7
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PARAMETER MEASUREMENT INFORMATION
CS(1)
tCSPW
tCSSC
tSCLK
tSPW
SCLK
tSPW
tDIST
DIN
tDIHD
Hi-Z
tDOPD
Hi-Z
DOUT
tCSDO
tDOHD
(1) CS can be tied low.
Figure 1. Serial Interface Timing
SERIAL INTERFACE TIMING CHARACTERISTICS
At TA= –40°C to +105°C and DVDD = 2.7V to 5.25V, unless otherwise noted.
SYMBOL
(1)
(2)
(3)
(4)
DESCRIPTION
MIN
MAX
UNITS
τCLK
2
(1)
tSCLK
SCLK period
tSPW
SCLK high or low pulse width (exceeding max resets SPI interface)
0.8
tCSSC
CS low to first SCLK: setup time
(3)
2.5
τCLK
tDIST
Valid DIN to SCLK rising edge: setup time
10
ns
tDIHD
Valid DIN to SCLK rising edge: hold time
5
ns
tDOPD
SCLK falling edge to valid new DOUT: propagation delay
tDOHD
SCLK falling edge to old DOUT invalid: hold time
tCSDO
CS high to DOUT invalid (3-state)
tCSPW
CS pulse width high
4096 (2)
(4)
τCLK
20
ns
5
τCLK
0
ns
τCLK
2
τCLK = master clock period = 1/fCLK.
Programmable to 256 τCLK.
CS can be tied low.
DOUT load = 20pF || 100kΩ to DGND.
tDRDY
DRDY
tDDO
DOUT
Figure 2. DRDY Update Timing
DRDY UPDATE TIMING CHARACTERISTICS
SYMBOL
t DRDY
tDDO
DESCRIPTION
DRDY high pulse width without data read
Valid DOUT to DRDY falling edge (CS = 0)
TYP
UNITS
1
τCLK
0.5
τCLK
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TYPICAL CHARACTERISTICS
At TA = +25°C, AVDD = +2.5V, AVSS = –2.5V, DVDD = +3.3V, fCLK = 16MHz (external clock) or fCLK = 15.729MHz (internal clock), OPA227
buffer between MUX outputs and ADC inputs, VREFP = +2.048V, and VREFN = –2.048V, unless otherwise noted.
OFFSET WITH 0.5V REFERENCE, CHOPPING ON
OFFSET WITH 4.096V REFERENCE, CHOPPING ON
6000
3500
25 Units,
254 Samples/Unit
25 Units, 256 Samples/Unit
3000
Number of Occurrences
Number of Occurrences
5000
4000
3000
2000
2500
2000
1500
1000
1000
500
0
0
-4
-3
-2
1
0
-1
2
3
-2
1
0
-1
Offset (Output Code)
2
Offset (Output Code)
Figure 3.
Figure 4.
OFFSET vs TEMPERATURE
GAIN ERROR HISTOGRAM
100
40
50
35
CHOP = 1
Number of Occurrences
Normalized Offset (mV)
150 Units From Two Production Sets
0
-50
-100
CHOP = 0
-150
-200
30
25
20
15
10
5
-250
0
10
-15
35
60
85
110
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
1600
1700
1800
1900
2000
-40
Temperature (°C)
Absolute Gain Error (ppm)
Figure 5.
Figure 6.
GAIN DRIFT HISTOGRAM
GAIN ERROR vs TEMPERATURE
30
60
150 Units From Two Production Sets
Normalized Gain Error (ppm)
40
Number of Occurrences
25
20
15
10
5
20
0
-20
-40
-60
-80
-100
-120
0
3.8
2.7
3.3
1.5
2.1
0.3
0.9
-0.9
-0.3
-1.5
-2.1
-2.7
-3.3
-3.8
-140
-40
-15
10
35
60
85
110
Temperature (°C)
Gain Drift (ppm/°C)
Figure 7.
8
Figure 8.
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TYPICAL CHARACTERISTICS (continued)
At TA = +25°C, AVDD = +2.5V, AVSS = –2.5V, DVDD = +3.3V, fCLK = 16MHz (external clock) or fCLK = 15.729MHz (internal
clock), OPA227 buffer between MUX outputs and ADC inputs, VREFP = +2.048V, and VREFN = –2.048V, unless otherwise
noted.
INTEGRAL NONLINEARITY vs VREF
INTEGRAL NONLINEARITY vs INPUT LEVEL
10
8
9
6
4
Linearity Error (ppm)
Linearity Error (ppm)
8
7
6
5
4
3
VREF = 4.096V
2
0
-2
-4
2
TA = -40°C
TA = -10°C
TA = +25°C
-6
1
-8
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
-5
-4
-3
-2
TA = +55°C
TA = +85°C
TA = +105°C
-1
Figure 9.
INL vs TEMPERATURE
2
3
4
5
OUTPUT SPECTRUM
0
f = 1kHz, -0.5dBFS
DRATE[1:0] = 11
32768 Points
-20
6
-40
Level (dBFS)
5
INL (ppm)
1
Figure 10.
7
4
3
-60
-80
-100
-120
-140
2
-160
1
-180
0
-200
-40
10
-15
35
60
85
110
1
Temperature (°C)
100
1k
10k
100k
Figure 12.
TEMPERATURE SENSOR VOLTAGE vs TEMPERATURE
TEMPERATURE SENSOR READING HISTOGRAM
8
220
ADS1158 and Test PCB Temperatures
Forced Together
35 Units From Two Production Sets
7
Number of Occurrences
200
190
180
170
160
ADS1158 Only Temperature Forced,
Test PCB in Free Air
150
140
6
5
4
3
2
1
130
120
0
-40
-20
0
20
40
60
80
100
120
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
210
10
Frequency (Hz)
Figure 11.
Temperature Sensor Voltage (mV)
0
VIN (V)
VREF (V)
Temperature (°C)
Temperature Reading (°C)
Figure 13.
Figure 14.
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TYPICAL CHARACTERISTICS (continued)
At TA = +25°C, AVDD = +2.5V, AVSS = –2.5V, DVDD = +3.3V, fCLK = 16MHz (external clock) or fCLK = 15.729MHz (internal
clock), OPA227 buffer between MUX outputs and ADC inputs, VREFP = +2.048V, and VREFN = –2.048V, unless otherwise
noted.
SENSOR BIAS CURRENT SOURCE RATIO vs
TEMPERATURE
SENSOR BIAS CURRENT SOURCE RATIO HISTOGRAM
14
17.5
17.0
10
Ratio (mA/mA)
Number of Occurrences
12
18.0
25 Units From
One Production Lot
8
6
4
16.5
16.0
15.5
15.0
2
14.5
0
14.0
-40
14.0 14.5 15.0 15.5 16.0 16.5 17.0 17.5 18.0 18.5 19.0
10
-15
35
Figure 15.
SUPPLY CURRENT vs TEMPERATURE
4
Unipolar
AVSS = 0V, AVDD = 5V
AVDD/AVSS
0.8
6
0.6
4
0.4
2
0.2
3
Current (mA)
8
DVDD Current (mA)
AVDD/AVSS Current (mA)
110
POWER-DOWN CURRENT vs TEMPERATURE
1.0
2
1
AVSS/AVDD
DVDD
0
0
0
-15
85
Figure 16.
10
-40
60
Temperature (°C)
Ratio (mA/mA)
10
35
60
85
110
-40
10
-15
Temperature (°C)
35
60
85
110
Temperature (°C)
Figure 17.
Figure 18.
POWER-DOWN CURRENT vs TEMPERATURE
140
Bipolar
AVSS = -2.5V, AVDD = 2.5V
120
Current (mA)
100
AVSS
80
60
40
20
AVDD
0
-40
-15
10
35
60
85
110
Temperature (°C)
Figure 19.
10
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OVERVIEW
The ADS1158 is a flexible, 16-bit, low-noise ADC
optimized for fast multi-channel, high-resolution
measurement systems. The converter provides a
maximum channel scan rate of 23.7kSPS, giving a
complete 16-channel scan in less than 700μs.
The ADS1158 converter consists of a fourth-order,
delta-sigma modulator followed by a programmable
digital filter. The modulator measures the differential
input signal, VIN = (ADCINP – ADCINN), against the
differential reference input, VREF = (VREFP –
VREFN). The digital filter receives the modulator
signal and provides a low-noise digital output. The
ADC channel block controls the multiplexer
Auto-Scan feature. Channel Auto-Scan occurs at a
maximum rate of 23.7kSPS. Slower scan rates can
be used with corresponding increases in resolution.
Figure 20 shows the block diagram of the ADS1158.
The input multiplexer selects which analog input pins
connect
to
the
multiplexer
output
pins
(MUXOUTP/MUXOUTN). External signal conditioning
can be used between the multiplexer output pins and
the ADC input pins (ADCINP/ADCINN) or the
multiplexer output can be routed internally to the ADC
inputs without external circuitry. Selectable current
sources within the input multiplexer can be used to
bias sensors or detect for a failed sensor. On-chip
system function readings provide readback of
temperature, supply voltage, gain, offset, and external
reference.
AVDD
DVDD
Communication is handled over an SPI-compatible
serial interface with a set of simple commands to
control the ADS1158. Onboard registers store the
various settings for the input multiplexer, sensor
detect bias, data rate selection, etc. Either an
external 32.768kHz crystal, connected to pins XTAL1
and XTAL2, or an external clock applied to pin CLKIO
can be used as the clock source. When using the
external crystal oscillator, the system clock is
available as an output for driving other devices or
controllers. General-purpose digital I/Os (GPIO)
provide input and output control of eight pins.
GPIO[7:0]
CLKIO CLKSEL PLLCAP XTAL2
XTAL1
Clock Control
GPIO
AIN0
Sensor
Bias
AIN1
CS
AIN2
SPI
Interface
AIN3
AIN4
DOUT
DRDY
AIN6
AIN8
DIN
Temperature
Supply Monitor
AIN5
AIN7
SCLK
16-Channel
MUX
Control
Logic
ADC Channel Control
PWDN
RESET
START
AIN9
AIN10
Internal Ref
AIN11
AIN12
Ext Ref Monitor
AIN13
Digital Filter
ADC
AIN14
AIN15
AINCOM
AVSS
MUXOUTP MUXOUTN
ADCINP
ADCINN VREFN VREFP
GND
Figure 20. ADS1158 Block Diagram
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MULTIPLEXER INPUTS
A simplified diagram of the input multiplexer is
illustrated in Figure 22. The multiplexer connects one
of 16 single-ended external inputs, one of eight
differential external inputs, or one of the on-chip
internal variables to the ADC inputs. The output of the
channel multiplexer can be routed to external pins
and then to the input of the ADC. This flexibility
allows for use of external signal conditioning. See the
External Multiplexer Loop section.
Electrostatic discharge (ESD) diodes protect the
analog inputs. To keep these diodes from turning on,
make sure the voltages on the input pins do not go
below AVSS by more than 100mV, and likewise do
not exceed AVDD by more than 100mV:
AVSS – 100mV < (Analog Inputs) < AVDD + 100mV.
The load presented by the switched capacitor can be
modeled with an effective resistance (Reff) of 40kΩ for
fCLK = 16MHz. Note that the effective impedance of
the reference inputs loads an external reference with
a non-zero source impedance.
AVDD
ESD
Diodes
VREFP
3pF
VREFN
ESD
Diodes
Overdriving the multiplexer inputs may affect the
conversions of other channels. See the Input
Overload Protection description in the Hardware
Considerations segment of the Applications section.
The converter supports two modes of channel access
through the multiplexer: the Auto-Scan mode and the
Fixed-Channel mode. These modes are selected by
the MUXMOD bit of register CONFIG0. The
Auto-Scan mode scans through the selected
channels automatically, with break-before-make
switching. The Fixed-Channel mode requires the user
to set the channel address for each channel
measured.
VOLTAGE REFERENCE INPUTS
(VREFP, VREFN)
The voltage reference for the ADS1158 ADC is the
differential voltage between VREFP and VREFN:
VREF = VREFP – VREFN. The reference inputs use a
structure similar to that of the analog inputs with the
circuitry on the reference inputs shown in Figure 21.
12
Reff = 40kW
(fCLK = 16MHz)
AVSS
Figure 21. Simplified Reference Input Circuit
ESD diodes protect the reference inputs. To keep
these diodes from turning on, make sure the voltages
on the reference pins do not go below AVSS by more
than 100mV, and likewise do not exceed AVDD by
100mV:
AVSS - 100mV < (VREFP or VREFN) < AVDD + 100mV
A high-quality reference voltage is essential to
achieve the best performance from the ADS1158.
Noise and drift on the reference degrade overall
system performance. It is especially critical that
special care be given to the circuitry that generates
the reference voltages and the layout when operating
in the low-noise settings (that is, with low data rates)
to prevent the voltage reference from limiting
performance. See the Reference Inputs description in
the Hardware Considerations segment of the
Applications section.
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VREFP
VREFN
Multiplexer
Reference/Gain Monitor
AIN0
AIN1
AIN2
Temperature Sensor Monitor
AVDD
AIN3
1x
AIN4
2x
AIN5
8x
1x
AIN6
AVSS
AIN7
Supply Monitor
AIN8
AVDD
AVSS
AIN9
AIN10
AIN11
NOTE: ESD diodes not shown.
Internal
Reference
AIN12
AVSS
AIN13
AIN14
ADC
AIN15
AINCOM
ADCINN
ADCINP
Offset Monitor
MUXOUTP
Sensor Bias
(AVDD - AVSS)/2
MUXOUTN
AVSS AVDD
Figure 22. Input Multiplexer
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ADC INPUTS
The ADS1158 ADC inputs (ADCINP, ADCINN)
measure the input signal using internal capacitors
that are continuously charged and discharged. The
left side of Figure 24 shows a simplified schematic of
the ADC input circuitry; the right side of Figure 24
shows the input circuitry with the capacitors and
switches replaced by an equivalent circuit. Figure 23
shows the ON/OFF timings of the switches shown in
Figure 24. S1 switches close during the input
sampling phase. With S1 closed, CA1 charges to
ADCINP, CA2 charges to ADCINN, and CB charges to
(ADCINP – ADCINN). For the discharge phase, S1
opens first and then S2 closes. CA1 and CA2 discharge
to approximately AVSS + 1.3V and CB discharges to
0V. This two-phase sample/discharge cycle repeats
with a period of tSAMPLE = 2/fCLK.
inputs. The average value of this current can be used
to calculate an effective impedance (Reff) where Reff =
VIN/IAVERAGE. These impedances scale inversely with
fCLK. For example, if fCLK is reduced by a factor of
two, the impedances will double.
As with the multiplexer and reference inputs, ESD
diodes protect the ADC inputs. To keep these diodes
from turning on, make sure the voltages on the input
pins do not go below AVSS by more than 100mV,
and likewise do not exceed AVDD by more than
100mV.
tSAMPLE
ON
S1
OFF
ON
S2
The charging of the input capacitors draws a transient
current from the source driving the ADS1158 ADC
OFF
Figure 23. S1 and S2 Switch Timing for Figure 24
AVSS + 1.3V
AVSS + 1.3V
S2
ReffA = 190kW
CA1 = 0.65pF
S1
Equivalent
Circuit
ADCINP
ADCINP
ReffB = 78kW
CB = 1.6pF
S1
(fCLK = 16MHz)
ADCINN
ADCINN
ReffA = 190kW
CA2 = 0.65pF
S2
Reff = tSAMPLE/CX
AVSS + 1.3V
AVSS + 1.3V
RAIN = ReffB || 2ReffA
NOTE: ESD input diodes not shown.
Figure 24. Simplified ADC Input Structure
14
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MASTER CLOCK (fCLK)
The ADS1158 oversamples the analog input at a high
rate. This oversampling requires a high-frequency
master clock to be supplied to the converter. As
shown in Figure 25, the clock comes from either an
internal oscillator (with external crystal), or an
external clock source.
50W
CLKSEL XTAL1
XTAL2
32.768kHz
CLKIO
Clock Output
(15.729MHz)
AVSS
0V to -2.5V
PLLCAP
(1)
22nF
CLKENB
Bit
4.7pF
(1) Parallel resonant type. CL = 12.5pF, ESR = 35kΩ (max). Place
the crystal and load capacitors as close as possible to the device
pins.
Internal Master Clock (fCLK)
MUX
4.7pF
Figure 26. Crystal Oscillator Connection
CLKIO
Table 1. System Clock Source
Oscillator
and PLL
CLKSEL
PIN
CLKENB
BIT
CLOCK SOURCE
CLKIO FUNCTION
PLL
0
32.768kHz
crystal oscillator
0
Disabled
(internally grounded)
Figure 25. Clock Generation Block Diagram
0
32.768kHz
crystal oscillator
1
Output (15.729MHz)
1
External clock input
X
Input (16MHz)
CLKSEL
XTAL1
XTAL2
The CLKSEL pin determines the source of the
system clock, as shown in Table 1. The CLKIO pin
functions as an input or as an output. When the
CLKSEL pin is set to '1', CLKIO is configured as an
input to receive the master clock. When the CLKSEL
pin is set to '0', the crystal oscillator generates the
clock. The CLKIO pin can then be configured to
output the master clock. When the clock output is not
needed, it can be disabled to reduce device power
consumption.
Crystal Oscillator
An on-chip oscillator and phase-locked loop (PLL)
together with an external crystal can be used to
generate the system clock. For this mode, tie the
CLKSEL pin low. A 22nF PLL filter capacitor,
connected from the PLLCAP pin to the AVSS pin, is
required. The internal clock of the PLL can be output
to the CLKIO to drive other converters or controllers.
If not used, disable the clock output to reduce device
power consumption; see Table 1 for settings. The
clock output is enabled by a register bit setting
(default is ON). Figure 26 shows the oscillator
connections. Place these components as close to the
pins as possible to avoid interference and coupling.
Do not connect XTAL1 or XTAL2 to any other logic.
The oscillator start-up time may vary, depending on
the crystal and ambient temperature. The user should
verify the oscillator start-up time.
Table 2. Approved Crystal Vendors
VENDOR
CRYSTAL PRODUCT
Epson
C-001R
Epson
MC-306 32.7680K-A0
Epson
FC-135 32.7680KA-A0
ECS
ECS-.327-12.5-17-TR
External Clock Input
When using an external clock to operate the device,
apply the master clock to the CLKIO pin. For this
mode, the CLKSEL pin is tied high. CLKIO then
becomes an input, as shown in Figure 27.
50W
CLKIO
2.7V
to 5V
Clock Input
(16MHz)
DVDD
CLKSEL
XTAL1
XTAL2
PLLCAP
No Connection
Figure 27. External Clock Connection
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Make sure to use a clock source clean from jitter or
interference. Ringing or under/overshoot should be
avoided. A 50Ω resistor in series with the CLKIO pin
(placed close to the source) can often help.
ADC
The ADC block of the ADS1158 is composed of two
blocks: a modulator and a digital filter.
Modulator
The modulator converts the analog input voltage into
a pulse code modulated (PCM) data stream. When
the level of differential analog input (ADCINP –
ADCINN) is near the level of the reference voltage,
the '1' density of the PCM data stream is at its
highest. When the level of the differential analog input
is near zero, the PCM '0' and '1' densities are nearly
equal. The fourth-order modulator shifts the
quantization noise to a high frequency (out of the
passband) where the digital filter can easily remove it.
The modulator continuously chops the input, resulting
in excellent offset and offset drift performance. It is
important to note that offset or offset drift that
originates from the external circuitry is not removed
by the modulator chopping. These errors can be
effectively removed by using the external chopping
feature of the ADS1158 (see the External Chopping
section).
Digital Filter
The programmable low-pass digital filter receives the
modulator output and produces a high-resolution
digital output. By adjusting the amount of filtering,
tradeoffs can be made between resolution and data
rate—filter more for higher resolution, filter less for
higher data rate. The filter consists of two sections, a
fixed filter followed by a programmable filter.
Figure 28 shows the block diagram of the filter. Data
are supplied to the filter from the analog modulator at
a rate of fCLK/2. The fixed filter is a fifth-order sinc
filter with a decimation value of 64 that outputs data
at a rate of fCLK/128. The second stage of the filter is
a programmable averager (first-order sinc filter) with
the number of averages set by the DRATE[1:0] bits.
The data rate depends upon the system clock
frequency (fCLK) and the converter configuration. The
data rate can be computed by Equation 1 or
Equation 2:
Data rate (Auto-Scan):
fCLK
128(411b - DR + 4.26525 + TD) ´ 2CHOP
(1)
Data rate (Fixed-Channel mode):
fCLK
128[411b - DR + CHOP(4.26525 + TD)] ´ 2CHOP
(2)
Where:
DR = DRATE[1:0] register bits (binary).
CHOP = Chop register bit.
TD = time delay value given in Table 4 from the
DLY[2:0] register bits (128/fCLK periods).
Modulator Rate = fCLK/2
Analog
Modulator
Data Rate = fCLK/128
5
sinc
Filter
Data Rate
(1)
= fCLK/(128 ´ Num_Ave)
Programmable
Averager
Num_Ave
(1) Data rate for Fixed-Channel mode, Chop = 0, Delay = 0.
Figure 28. Block Diagram of Digital Filter
16
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Table 3 shows a listing of the averaging and data
rates for each of the four DRATE[1:0] register
settings for the Auto-Scan and Fixed-Channel modes,
with CHOP, DLY = 0. Note that the data rate scales
directly with fCLK. For example, reducing fCLK by 2x
reduces the maximum data rate by 2x.
Figure 30 shows the response with averaging set to 4
(DRATE[1:0] = 10). 4-reading, post-averaging
produces three equally-spaced notches between
each main notch of the sinc5 filter. The frequency
response of DRATE[1:0] = 01 and 00 follows a similar
pattern, but with 15 and 63 equally-spaced notches
between the main sinc5 notches, respectively.
FREQUENCY RESPONSE
5
½H(f)½ = ½Hsinc (f)½ ´ ½HAverager(f)½ =
sin
128p ´ f
fCLK
64 ´ sin
2p ´ f
fCLK
5
sin
´
0
Data Rate
Auto-Scan Mode
(23.739kSPS)
-20
-40
Gain (dB)
The low-pass digital filter sets the overall frequency
response for the ADS1158. The filter response is the
product of the responses of the fixed and
programmable filter sections and is given by
Equation 3:
128p ´ Num_Ave ´ f
fCLK
Data Rate
Fixed-Channel Mode
(125kSPS)
-60
-80
-100
-120
128p ´ f
Num_Ave ´ sin
fCLK
-140
0
125
250
(3)
The low-pass filter has notches (or zeros) at the data
output rate and multiples thereof. The sinc5 part of
the filter produces wide notches at fCLK/128 and
multiples thereof. At these frequencies, the filter has
zero gain. Figure 29 shows the response with no post
averaging. Note that in Auto-Scan mode, the data
rate is reduced while retaining the same frequency
response as in Fixed-Channel mode.
With programmable averaging, the wide notches
produced by the sinc5 filter remain, but a number of
narrow notches are superimposed in the response.
The number of the superimposed notches is
determined
by
the
number
of
readings
averaged (minus one).
500
625
Figure 29. Frequency Response, DRATE[1:0] = 11
0
Data Rate
Auto-Scan Mode
(15.123kSPS)
-20
-40
Gain (dB)
The digital filter attenuates noise on the modulator
output, including noise from within the ADS1158 and
external noise present within the ADS1158 input
signal. Adjusting the filtering by changing the number
of averages used in the programmable filter changes
the filter bandwidth. With a higher number of
averages, the bandwidth is reduced and more noise
is attenuated.
375
Frequency (kHz)
Data Rate
Fixed-Channel Mode
(31.25kSPS)
-60
-80
-100
-120
-140
0
125
250
375
500
625
Frequency (kHz)
Figure 30. Frequency Response, DRATE[1:0] = 10
Table 3. Data Rates (1)
(1)
(2)
(3)
DRATE[1:0]
Num_Ave (2)
DATA RATE AUTO-SCAN
MODE (SPS) (3)
DATA RATE FIXED-CHANNEL
MODE (SPS)
–3dB BANDWIDTH
(Hz)
11
1
23739
125000
25390
10
4
15123
31250
12402
01
16
6168
7813
3418
00
64
1831
1953
869
fCLK = 16MHz, Chop = 0, and Delay = 0.
Num_Ave is the number of averages performed by the digital filter second stage.
In Auto-Scan mode, the data rate listed is for a single channel; the effective data rate for multiple channels (on a per-channel basis) is
the value shown in Figure 29 and Figure 30 divided by the number of active channels in a scan loop.
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ALIASING
The digital filter low-pass characteristic repeats at
multiples of the modulator rate of fCLK/2. Figure 31
shows the response plotted out to 16MHz at the data
rate of 125kSPS (Fixed-Channel mode). Notice how
the responses near dc, 8MHz, and 16MHz are the
same. The digital filter attenuates high-frequency
noise on the ADS1158 inputs up to the frequency
where the response repeats. However, noise or
frequency components present on the analog input
where the response repeats alias into the passband.
For most applications, an anti-alias filter is
recommended to remove this noise. A simple
first-order input filter with a pole at 200kHz
provides –34dB rejection at the first image frequency.
applying asynchronous step inputs, the settling time
is somewhat different. The step-input settling time
diagrams (Figure 32 and Figure 33) show the
converter step response with an asynchronous step
input. For most modes of operation, the analog input
must be stable for one complete conversion cycle to
provide settled data. In Fixed-Channel mode
(DRATE[1:0] = 11), the input must be stable for five
complete conversion cycles.
Data Not Settled
Settled Data
1
DRDY
2
Step Input
0
Figure 32. Asynchronous Step-Input Settling
Time (DRATE[1:0] = 10, 01, 00)
DRATE[1:0] = 11
125kSPS
Fixed-Channel Mode
-20
Gain (dB)
-40
Data Not Settled
-60
1
DRDY
-80
Settled Data
2
6
-100
Step Input
-120
-140
0
4
8
12
Figure 33. Asynchronous Step-Input Settling
Time (Fixed-Channel Mode, DRATE[1:0] = 11)
16
Frequency (MHz)
Figure 31. Frequency Response Out to 16MHz
Referring to Figure 29 and Figure 30, frequencies
present on the analog input above the Nyquist rate
(sample rate/2) are first attenuated by the digital filter
and then aliased into the passband.
SETTLING TIME
The design of the ADS1158 provides fully-settled
data when scanning through the input channels in
Auto-Scan mode. The DRDY flag asserts low when
the data for each channel are ready. It may be
necessary to use the automatic switch time delay
feature to provide time for settling of the external
buffer and associated components after channel
switching. When the converter is started (START pin
transitions high or Start Command) with stable inputs,
the first converter output is fully settled. When
18
Table 4. Effective Data Rates with Switch-Time
Delay (Auto-Scan Mode) (1)
DLY
[2:0]
TIME
DELAY
(128/fCLK
periods)
TIME
DELAY
(μS)
DRATE
[1:0] =
11
DRATE
[1:0] =
10
DRATE
[1:0] =
01
DRATE
[1:0] =
00
000
0
0
23739
15123
6168
1831
001
1
8
19950
13491
5878
1805
010
2
16
17204
12177
5614
1779
011
4
32
13491
10191
5151
1730
100
8
64
9423
7685
4422
1639
101
16
128
5878
5151
3447
1483
110
32
256
3354
3104
2392
1247
111
48
384
2347
2222
1831
1075
(1)
Time delay and data rates scale with fCLK. If Chop = 1, the
data rates are half those shown. fCLK = 16MHz, Auto-Scan
mode.
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EXTERNAL MULTIPLEXER LOOP
The external multiplexer loop consists of two
differential multiplexer output pins and two differential
ADC input pins. The user may use external
components (buffering/filtering, single-ended to
differential conversion, etc.) to form a signal
conditioning loop. For best performance, the ADC
input should be buffered and driven differentially.
To bypass the external multiplexer loop, connect the
ADC input pins directly to the multiplexer output pins,
or select internal bypass connection (BYPASS = 0 of
CONFIG0). Note that the multiplexer output pins are
active regardless of the bypass setting.
Use of the switch time delay register reduces the
effective channel data rate. Table 4 shows the actual
data rates derived from Equation 1, when using the
switch time delay feature.
When pulse converting, where one channel is
converted with each START pin pulse or each pulse
command, the application software may provide the
required time delay between pulses. However, with
Chop = 1, the switch time delay feature may continue
to be necessary to allow for settling.
In estimating the time delay that may be required,
Table 5 lists the time delay-to-time constant ratio (t/τ)
and the corresponding final settled data in % and
number of bits.
SWITCH TIME DELAY
When using the ADS1158 in the Auto-Scan mode,
where the converter automatically switches from one
channel to the next, the settling time of the external
signal conditioning circuit becomes important. If the
channel does not fully settle after the multiplexer
channel is switched, the data may not be correct. The
ADS1158 provides a switch time delay feature which
automatically provides a delay after channel switching
to allow the channel to settle before taking a reading.
The amount of time delay required depends primarily
on the settling time of the external signal conditioning.
Additional consideration may be needed to account
for the settling of the input source arising from the
transient generated from channel switching.
Table 5. Settling Time
t/τ (1)
FINAL SETTLING
(%)
FINAL SETTLING
(Bits)
1
63
2
3
95
5
5
99.3
7
7
99.9
10
10
99.995
14
15
99.998
16
(1) Multiple time
(τ1 2 + τ2 2+…).
constants
can
be
approximated
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SENSOR BIAS
An integrated current source provides a means to
bias an external sensor (for example, a diode
junction); or, it verifies the integrity of a sensor or
sensor connection. When the sensor fails to an open
condition, the current sources drive the inputs of the
converter to positive full-scale. The biasing is in the
form of differential currents (programmable 1.5μA or
24μA), connected to the output of the multiplexer.
Figure 34 shows a simplified diagram of ADS1158
input structure with the external sensor modeled as a
resistance RS between two input pins. The two 80Ω
series resistors, RMUX, model the ADS1158 internal
resistances. RL represents the effective input
resistance of the ADC input or external buffer. When
the sensor bias is enabled, they source ISDC to one
selected input pin (connected to the MUXOUTP
channel) and sink ISDC from the other selected input
pin (connected to the MUXOUTN channel). The
signal measured with the biasing enabled equals the
total IR drop: ISDC[(2RMUX + RS) ‫ ׀׀‬RL]. Note that when
the sensor is a direct short (that is, RS = 0), there
continues to be a small signal measured by the
ADS1158 when the biasing is enabled: ISDC[2RMUX ‫׀׀‬
RL].
AVDD
ISDC
80W
MUXOUTP
ADCINP
RS
The time to charge the external capacitance is given
in Equation 4:
ISDC
dV
=
dt
C
(4)
It is also important to note that the low impedance
(65kΩ) of the direct ADC inputs or the impedance of
the external signal conditioning loads the current
sources. This low impedance limits the ability of the
current source to pull the inputs to positive full-scale
for open-channel detection.
OPEN-SENSOR DETECTION
For open-sensor detection, set the biasing to either
1.5μA or 24μA. Then select the channel and read the
output code. When a sensor opens, the positive input
is pulled to AVDD and the negative input is pulled to
AVSS. Because of this configuration, the output code
trends toward positive full-scale. Note that the
interaction of the multiplexer resistance with the
current source may lead to degradation in converter
linearity. It is recommended to enable the current
source only periodically to check for open inputs and
discard the associated data.
RL
80W
ADCINN
MUXOUTN
EXTERNAL DIODE BIASING
The current source can be used to bias external
diodes for temperature sensing. Scan the appropriate
channels with the current source set to 24µA.
Re-scan the same channels with the current source
set to 1.5µA. The difference in diode voltage readings
resulting from the two bias currents is directly
proportional to temperature.
ISDC
AVSS
Figure 34. Sensor Bias Structure
20
The current source is connected to the output of the
multiplexer. For unselected channels, the current
source is not connected. This configuration means
that when a new channel is selected, the current
source charges stray sensor capacitance, which may
slow the rise of the sensor voltage. The automatic
switch time delay feature can be used to apply an
appropriate time delay before a conversion is started
to provide fully settled data (see the Switch Time
Delay section).
Note that errors in current ratio, diode and cable
resistance, or the non-ideality factor of the diode can
lead to errors in temperature readings. These effects
can be compensated by characterization or by
calibrating the diode at known temperatures.
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EXTERNAL CHOPPING
GPIO DIGITAL PORT (GPIOx)
The modulator of the ADS1158 incorporates a
chopping front-end that removes offset errors to
provide excellent offset and offset drift performance.
However, offset and offset drift that originate from
external signal conditioning are not removed by the
modulator. The ADS1158 has an additional chopping
feature that removes external offset errors (CHOP =
1).
The ADS1158 has eight dedicated general-purpose
digital input/output (GPIO) pins. The digital I/O pins
are individually configurable as either inputs or as
outputs through the GPIOC (GPIO-Configure)
register. The GPIOD (GPIO-Data) register controls
the level of the pins. When reading the GPIOD
register, the data returned are the level of the pins,
whether they are programmed as inputs or outputs.
As inputs, a write to the GPIOD has no effect. As
outputs, a write to the GPIOD sets the output value.
With external chopping enabled, the converter takes
two readings in succession on the same channel. The
first reading is taken with one polarity and the second
reading is taken with the opposite polarity. The
converter averages the two readings and cancels the
offset, as shown in Figure 35. With chopping enabled,
the effective reading reduces to half of the nominal
reading rate.
During Standby and Power-Down modes, the GPIO
remains active. If configured as inputs, these pins
must be driven (do not float). If configured as outputs,
the pins are driven. The GPIO pins are set as inputs
after power-on or after a reset. Figure 36 shows the
GPIO port structure.
Multiplexer
(chopping)
MUXOUTP
AINn
GPIO Data (read)
ADCINP
Optional
Signal
Conditioning
GPIO Pin
ADC
GPIO Data (write)
AINn
MUXOUTN
ADCINN
Figure 35. External Chopping
GPIO Control
Note that because the inputs are reversed under
control of the ADS1158, a delay time may be
necessary to provide time for external signal
conditioning to fully settle before the second phase of
the reading sequence starts (see the Switch Time
Delay section).
External chopping can be used to reduce total offset
errors and offset drift over temperature. Note that
chopping must be disabled (CHOP = 0) in order to
take the internal monitor readings.
Figure 36. GPIO Port Pin
POWER-DOWN INPUT (PWDN)
The PWDN pin controls the power-down mode of the
converter. In power-down mode, all internal circuitry
is deactivated including the oscillator and the clock
output. Hold PWDN low for at least two fCLK cycles to
engage power-down. The register settings are
retained during power-down. When the pin is returned
high, the converter requires a wake-up time before
readings can be taken, as shown in the Power-Up
Timing section. Note that in power-down mode, the
inputs of the ADS1158 must continue to be driven
and the device continues to drive the outputs.
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Table 6. Wake-Up Times
POWER-UP TIMING
When powering up the device or taking the PWDN
pin high to wake the device, a wake-up time is
required before readings can be taken. When using
the internal oscillator, the wake-up time is composed
of the oscillator start-up time and the PLL lock time,
and if the supplies are also being powered, there is a
reset interval time of 218 fCLK cycles. Note that CLKIO
is not valid during the wake-up period, as shown in
Figure 37.
tWAKE
INTERNAL
OSCILLATOR(1)
CONDITION
tWAKE
EXTERNAL CLOCK
PWDN or CLKSEL
tOSC
2/fCLK
AVDD – AVSS
tOSC + 218/fCLK
218/fCLK
(1) Wake-up times for the internal oscillator operation are typical
and may vary depending on crystal characteristics and layout
capacitance. The user should verify the oscillator start-up
times (tOSC = oscillator start-up time).
POWER-UP SEQUENCE
tWAKE
CLKIO
The analog and digital supplies should be applied
before any analog or digital input is driven. The power
supplies may be sequenced in any order. The internal
master reset signal is generated from the analog
power supply (AVDD – AVSS), when the level
reaches approximately 3.2V. The power-up master
reset signal is functionally the same as the Reset
Command and the RESET input pin.
PWDN
or
CLKSEL
or
Reset Input (RESET)
(1)
AVDD - AVSS
Device Ready
3.2V, typical
(1) Shown with DVDD stable.
Figure 37. Device Wake Time with
Internal Oscillator
When using the device with an external clock, the
wake-up time is 2/fCLK periods when waking up with
the PWDN pin and 218/fCLK periods when powering
the supplies, all after a valid CLKIO is applied, as
shown in Figure 38.
This pin selects the source of the system clock: the
crystal oscillator or an external clock. Tie CLKSEL
low to select the crystal oscillator. When using an
external clock (applied to the CLKIO pin), tie CLKSEL
high.
This pin serves either as a clock output or clock input,
depending on the state of the CLKSEL pin. When
using an external clock, apply the clock to this pin
and set the CLKSEL pin high. When using the
internal oscillator, this pin has the option of providing
a clock output. The CLKENB bit of register CONFIG0
enables the clock output (default is enabled).
CLKIO
PWDN,
CLKSEL
or
(1)
3.2V, typical
Device Ready
(1) Shown with DVDD stable.
Figure 38. Device Wake Time with External Clock
Table 6 summarizes the wake-up times using the
internal oscillator and the external clock operations.
22
Clock Select Input (CLKSEL)
Clock Input/Output (CLKIO)
tWAKE
AVDD - AVSS
When RESET is held low for at least two fCLK cycles,
all registers are reset to their default values and the
digital filter is cleared. When RESET is released high,
the device is ready to convert data.
Start Input (START)
The START pin is an input that controls the ADC
process. When the START pin is taken high, the
converter starts converting the selected input
channels. When the START pin is taken low, the
conversion in progress runs to completion and the
converter is stopped. The device then enters one of
the two idle modes (see the Idle Modes section for
more details). See the Conversion Control section for
details of using the START pin.
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Data Ready Output (DRDY)
The DRDY pin is an output that asserts low to
indicate when new channel data are available to read
(the previous conversion data are lost). DRDY returns
high after the first falling edge of SCLK during a data
read operation. If the data are not read (no SCLK
pulses), DRDY remains low until new channel data
are available once again. DRDY then pulses high,
then low to indicate new data are available; see
Figure 39.
DRDY
SCLK
DRDY is usually connected to an interrupt of a
controller, DSP, or connected to a controller port pin
for polling in a software loop. Channel data can be
read without the use of DRDY. Read the data using
the register format read and check the Status Byte
when the NEW bit = 1, which indicates new channel
data.
Output Data Scaling and Over-Range
The ADS1158 is scaled such that the output data
code resulting from an input voltage equal to ±VREF
has a margin of 6.6% before clipping. This
architecture allows operation of applied input signals
at or near full-scale without overloading the converter.
Specifically, the device is calibrated so that:
1LSB = VREF/7800h,
DRDY with SCLK
and the output clips when:
tDRDYPLS
DRDY
|VIN| ≥ 1.06 × VREF.
Table 7 summarizes the ideal output codes versus
input signals.
SCLK
DRDY without SCLK
tDRDYPLS =
1
fCLK
Figure 39. DRDY Timing
(See Figure 2 for the DRDY Pulse)
Table 7. Ideal Output Code versus Input Signal
INPUT SIGNAL VIN
(ADCINP – ADCINN)
IDEAL OUTPUT CODE (1)
≥ +1.06 VREF
7FFFh
Maximum positive full-scale before output clipping
+VREF
7800h
VIN = +VREF
+1.06 VREF/(215 – 1)
0001h
+1LSB
0
0000h
Bipolar Zero
–1.06 VREF/(215 – 1)
FFFFh
–1LSB
–VREF
87FFh
VIN = –VREF
8000h
Maximum negative full-scale before output clipping
15
15
≤ –1.06 VREF × (2 /2
(1)
DESCRIPTION
– 1)
Ideal output code –0.5LSB excludes effects of noise, linearity, offset, and gain errors.
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Reference Reading (REF)
INTERNAL SYSTEM READINGS
Analog Power-Supply Reading (VCC)
The analog power-supply voltage of the ADS1158
can be monitored by reading the VCC register. The
supply voltage is routed internal to the ADS1158 and
is measured and scaled using an internal reference.
The supply readback channel outputs the difference
between AVDD and AVSS (AVDD – AVSS), for both
single and dual configurations. Note that it is required
to disable chopping (CHOP = 0) before taking this
reading.
The scale factor of Equation 5 converts the code
value to volts:
Code
Total Analog Supply Voltage (V) =
3072 (C00h)
(5)
When the power supply falls below the minimum
specified operating voltage, the full operation of the
ADS1158 cannot be ensured. Note that when the
total analog supply voltage falls to below
approximately 4.3V, the returned data are set to zero.
The SUPPLY bit in the status byte is then set. The bit
clears when the total supply voltage rises
approximately 50mV higher than the lower trip point.
The digital supply (DVDD) may be monitored by
looping-back the supply voltage to an input channel.
A resistor divider may be required for bipolar supply
operation to reduce the DVDD level to within the
range of the analog supply.
Gain Reading (GAIN)
In this configuration, the external reference is
connected both to the analog input and to the
reference input of the ADC. The data from this
register indicate the gain of the device.
The following scale factor (Equation 6) converts the
code value to device gain:
Code
Device Gain (V/V) =
30720 (7800h)
(6)
To correct the device gain error, the user software
can divide each converter data value by the device
gain. Note that this corrects only for gain errors
originating within the ADC; system gain errors that
occur because of an external gain stage error or
because of reference errors are not compensated.
Note that it is also required to disable chopping
(CHOP = 0) before taking this reading.
24
In this configuration, the external reference is
connected to the analog input and an internal
reference is connected to the reference of the ADC.
The data from this register indicate the magnitude of
the external reference voltage.
The scale factor of Equation 7 converts the code
value to external reference voltage:
Code
External Reference (V) =
3072 (C00h)
(7)
This readback function can be used to check for
missing or an out-of-range reference. If the reference
input pins are floating (not connected), internal
biasing pulls them to the AVSS supply. This pull
causes the output code to tend toward '0'. Bypass
capacitors connected to the external reference pins
may slow the response of the pins when open. When
reading this register immediately after power-on,
verify that the reference has settled to ensure an
accurate reading. Note that it is required to disable
chopping (CHOP = 0) before taking this reading.
Temperature Reading (TEMP)
The ADS1158 contains an on-chip temperature
sensor. This sensor uses two internal diodes with one
diode having a current density of 16x of the other.
The difference in current densities of the diodes
yields a difference voltage that is proportional to
absolute temperature.
As a result of the low thermal resistance of the
package to the printed circuit board (PCB), the
internal device temperature tracks the PCB
temperature closely. Note also that self-heating of the
ADS1158 causes a higher reading than the
temperature of the surrounding PCB. Note that it is
required to disable chopping (CHOP = 0) before
taking this reading.
The scale factor of Equation 8 converts the
temperature reading to °C. Before using the equation,
the temperature reading code must first be scaled to
microvolts.
Temperature (°C) =
Temp Reading(mV) - 168,000mV
Temp Sensor Coefficient
+ 25°C
(8)
Where Temp Sensor Coeff = 563μV/°C (if the
ADS1158 and test PCB temperatures are forced
together), or 394μV/°C if only the ADS1158
temperature is forced and the test PCB is in free
air.
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Offset Reading (OFFSET)
Data Ready, Index to Next Channel
The differential output of the multiplexer is shorted
together and set to a common-mode voltage of
(AVDD – AVSS)/2. Ideally, the code from this register
function is 0h, but varies because of the noise of the
ADC and offsets stemming from the ADC and
external signal conditioning. This register can be used
to calibrate or track the offset of the ADS1158 and
external signal conditioning. The chop feature of the
ADC can automatically remove offset and offset drift
from the external signal conditioning; see the External
Chopping section.
CONVERSION CONTROL
The conversions of the ADS1158 are controlled by
the START pin. Conversions begin when the START
pin is taken high and conversions are stopped when
the START pin is taken low. For continuous
conversions, tie the START pin high. The START pin
can also be tied low and the conversions controlled
by the PULSE convert command. The PULSE
convert command converts one channel (only) for
each command sent. In this way, channel
conversions can be stepped without the need to
toggle the START pin.
START Pin
As shown in Figure 40, when the START pin is taken
high, conversions start beginning with the current
channel. The device continues to convert all of the
programmed channels, in a continuous loop, until the
START pin is taken low. When this occurs, the
conversion in process completes, and the device
enters the standby or sleep mode and waits for a new
start condition. When DRDY asserts low, the
conversion data are ready. Figure 42 shows the
START pin to DRDY timing. The order in which
channel data are converted is described in Table 9.
When the last selected channel in the program list
has been converted, the device continues
conversions starting with the highest priority channel.
If there is only one channel selected in the Auto-Scan
mode, the converter remains fixed on one channel. A
write operation to any of the multiplexer channel
select registers sets the channel pointer to the
highest priority channel (see Table 10). In
Fixed-Channel mode, the channel pointer remains
fixed.
Idle Mode
Converting
Idle
DRDY
START Pin
Figure 40. Conversion Control, Auto-Scan Mode
Pulse Convert Command
Figure 41 also shows the start of conversions with the
rising edge of the START pin. If the START pin is
taken high, and then low before completion of the
conversion cycle (8 τCLK before DRDY asserts low),
only the current channel is converted and the device
enters the standby or sleep modes and waits for a
new start condition. Figure 42 shows the START pin
to DRDY timing. The same function of conversion
control is possible using the Pulse Convert command
(with the START pin low). In this operation, the data
from one channel are converted with each Pulse
Convert command. The Pulse convert command
takes effect when the command byte is completely
shifted in (eighth falling edge of SCLK). After
conversion, if more than one channel is enabled
(Auto-Scan mode), the converter indexes to the next
selected channel after completing the conversion.
Data Ready, Index to Next Channel
Converting
Idle
Converting
DRDY
START Pin
or
Pulse Convert
Command
Figure 41. Pulse Conversion, Auto-Scan Mode
DRDY
tSDSU
tDRHD
START Pin
SYMBOL
DESCRIPTION
MIN
UNIT
tSDSU
START to DRDY Setup Time
to Halt Further Conversions
8
tCLK
tDRHD
DRDY to START Hold Time
to Complete Current Conversion
8
tCLK
Figure 42. START Pin and DRDY Timing
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GPIO Linked START Pin Control
The START pin can be controlled directly by software
by connecting externally a GPIO port pin to the
START pin. (Note that an external pull-down resistor
is recommended to keep the GPIO from floating until
the GPIO is configured as an output). For this mode
of control, the START pin is effectively controlled by
writing to the GPIO Data Register (GPIOD), with the
write operation setting or resetting the appropriate bit.
The data takes effect on the eighth falling edge of the
data byte write. The START pin can then be
controlled by the serial interface.
Initial Delay
As seen in Figure 43, when a start convert condition
occurs, the first reading from ADS1158 is delayed for
a number of clock cycles. This delay allows fully
settled data to occur at the first data read. Data reads
thereafter are available at the full data rate. The
number of clock cycles delayed before the first
reading is valid depends on the data rate setting, and
whether exiting the Standby or Sleep mode. Table 8
lists the delayed clock cycles versus data rate.
Fully-Settled Data
Power-Down mode. In Converting mode, the device
is actively converting channel data. The device power
dissipation is the highest in this mode. This mode is
divided into two sub-modes: Auto-Scan and
Fixed-Channel.
The next mode is the Idle mode. In this mode, the
device is not converting channel data. The device
remains active, waiting for input to start conversions.
The power consumption is reduced from that of the
Converting mode. This mode also has two
sub-modes: Standby and Sleep.
The last mode is Power-Down mode. In this mode, all
functions of the converter are disabled to reduce
power consumption to a minimum.
CONVERTING MODES
The ADS1158 has two converting modes: Auto-Scan
and Fixed-Channel. In Auto-Scan mode, the channels
to be measured are pre-selected in the address
register settings. When a convert condition is present,
the converter automatically measures and sequences
through the channels either in a continuous loop or
pulse-step fashion, depending on the trigger
condition.
In Fixed-Channel mode, the channel address is
selected in the address register settings before
acquiring channel data. When a convert condition is
present, the device converts a single channel, either
continuously or in pulse-step fashion, depending on
the trigger condition. The data rate in this mode is
higher than in Auto-Scan mode because the input
channels are not indexed for each reading.
DRDY
Initial Delay
Start
Condition
Figure 43. Start Condition to First Data
The selection of converting modes is set with bit
MUXMOD of register CONFIG0.
OPERATING MODES
The operating modes of the ADS1158 are defined in
three basic states: Converting mode, Idle mode, and
Table 8. Start Condition to DRDY Delay, Chop = 0, DLY[2:0] = 000
INITIAL DELAY (Standby Mode)
(fCLK cycles)
DRATE[1:0]
26
Fixed-Channel
Auto-Scan
INITIAL DELAY (Sleep Mode)
(fCLK cycles)
Fixed-Channel
Auto-Scan
11
802
708
866
772
10
1186
1092
1250
1156
01
2722
2628
2786
2692
00
8866
8772
8930
8836
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Auto-Scan Mode
Fixed-Channel Mode
The ADS1158 provides 16 analog inputs that can be
configured in combinations of eight differential inputs
or 16 single-ended inputs. The device also provides
an additional five internal system measurements.
Taken together, the device allows a total of 29
possible channel measurements. The converter
automatically scans and measures the selected
channels, either in a continuous loop or pulse-step
fashion, under the control of the START pin or Start
command software. The channels are selected for
measurement in registers MUXDIF, MUXSG0,
MUXSG1, and SYSRED. When any of these registers
are written, the internal channel pointer is set to the
channel address with the highest priority (see
Table 10).
In this mode, any of the 16 analog input channels
(AIN0–AIN15) can be selected for the positive ADC
input and any analog input channels can be selected
for the negative ADC input. New channel
configurations must be selected by the MUXSCH
DRDY asserts low when the channel data are ready;
see Figure 41 and Figure 40. At the same time, the
converter indexes to the next selected channel and, if
the START pin is high, starts a new channel
conversion. Otherwise, if pulse converting, the device
enters the Idle mode.
For example, if channels 3, 4, 7, and 8 are selected
for measurement in the list, the ADS1158 converts
the channels in that order, skipping all other
channels. After channel 8 is converted, the device
starts over, beginning at the top of the channel list,
channel 3.
The following guidelines can be used when selecting
input channels for Auto-Scan measurement:
1. For differential measurements, adjacent input
pins (AIN0/AIN1, AIN2/AIN3, AIN4/AIN5, etc.) are
pre-set as differential pairs. Even number
channels from each pair represent the positive
input to the ADC and odd number channels within
a pair represent the negative input (for example,
AIN0/AIN1: AIN0 is the positive channel, AIN1 is
the negative channel.)
2. For single-ended measurements, use AIN0
through AIN15 as single-ended inputs; AINCOM
is the shared common input among them. Note:
AINCOM does not need to be at ground potential.
For example, AINCOM can be tied to VREFP or
VREFN; or any potential between (AVSS –
100mV) and (AVDD + 100mV).
3. Combinations of differential, single-ended inputs,
and internal system registers can be used in a
scan.
register before converting a different channel. Note
that the AINCOM input and the internal system
registers cannot be referenced in this mode.
Idle Modes
When the START pin is taken low, the device
completes the conversion of the current channel and
then enters one of the Idle modes, Standby or Sleep.
In the Standby mode, the internal biasing of the
converter is reduced. This state provides the fastest
wake-up response when re-entering the run state. In
Sleep mode, the internal biasing is reduced further to
provide lower power consumption than the Standby
mode. This mode has a slower wake-up response
when re-entering the Converting mode (see Table 8).
Selection of these modes is set under bit IDLMOD of
register CONFIG1.
POWER-DOWN MODE
In power-down mode, both the analog and digital
circuitry are completely disabled.
SERIAL INTERFACE
The ADS1158 is operated via an SPI-compatible
serial interface by writing data to the configuration
registers, using commands to control the converter
and finally reading back the channel data. The
interface consists of four signals: CS, SCLK, DIN,
and DOUT.
Chip Select (CS)
CS is an input that selects the device for serial
communication. CS is active low. When CS is high,
read or write commands in progress are aborted and
the serial interface is reset. Additionally, DOUT goes
to a 3-state condition and inputs on DIN are ignored.
DRDY indicates when data are ready, independent of
CS.
The converter may be operated using CS to actively
select and deselect the device, or with CS tied low
(always selected). CS must stay low for the entire
read or write operation. When operating with CS tied
low, the number of SCLK pulses must be carefully
controlled to avoid false command transmission.
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Serial Clock (SCLK) Operation
Reading DATA
The serial clock (SCLK) is an input that is used to
clock data into (DIN) and out of (DOUT) the
ADS1158. This input is a Schmitt-trigger input that
has a high degree of noise immunity. However, it is
recommended to keep SCLK as clean as possible to
prevent glitches from inadvertently shifting the data.
Data are shifted into DIN on the rising edge of SCLK
and data are shifted out of DOUT on the falling edge
of SCLK. If SCLK is held inactive for 4096 or 256 fCLK
cycles (SPIRST bit of register CONFIG0), read or
write operations in progress terminate and the SPI
interface resets. This timeout feature can be used to
recover lost communication when a serial interface
transmission is interrupted or inadvertently glitched.
DRDY goes low to indicate that new conversion data
are ready. The data may be read via a direct data
read (Channel Data Read Direct) or in a register
format (Channel Data Read Register). A direct data
read requires the data to be read before the next
occurrence of DRDY or the data are corrupted. This
type of data read requires synchronization with DRDY
to avoid this conflict. When reading data in the
register format, the data may be read at any time
without concern to DRDY. The NEW bit of the
STATUS byte indicates that the data register has
been refreshed with new converter data since the last
read operation. The data are shifted out MSB first
after the STATUS byte.
Data Input (DIN) and Data Output (DOUT)
Operation
It should be noted that on system power-up, if the
ADS1158 interface signals are floating or undefined,
the interface could wake in an unknown state. This
condition is remedied by resetting the interface in
three ways: toggle the RESET pin low then high;
toggle the CS pin high then low; or hold SCLK
inactive for 218 + 4096 fCLK cycles.
The data input pin (DIN) is used to input data to the
ADS1158. The data output pin (DOUT) is used to
output data from the ADS1158. Data on DIN is shifted
into the converter on the rising edge of SCLK while
data are shifted out on DOUT on the falling edge of
SCLK. DOUT 3-states when CS is high to allow
multiple devices to share the line.
SPI Bus Sharing
The ADS1158 can be connected to a shared SPI bus.
DOUT 3-states when CS is deselected (high). When
the ADS1158 is connected to a shared bus, data can
be read only by the Channel Data Read command
format.
COMMUNICATION PROTOCOL
Communicating with the ADS1158 involves shifting
data into the device (via the DIN pin) or shifting data
out of the device (via the DOUT pin) under control of
the SCLK input.
28
Channel Data Read Direct
Channel data can be accessed from the ADS1158 in
two ways: Direct data read or data read with register
format. With Direct read, the DIN input pin is held
inactive (high or low) for at least the first three SCLK
transitions. When the first three bits are 000 or 111,
the device detects a direct data read and channel
data are output. After the device detects this read
format, commands are ignored until either CS is
toggled, an SPI timeout occurs or the device is reset.
The Channel Data Read command does not have
this requirement.
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Channel Data Read Command
Concurrent with the first SCLK transition, channel
data are output on the DOUT output pin. A total of 16
or 24 SCLK transitions complete the data read
operation. The number of shifts depend on whether
the status byte is enabled. The data must be
completely shifted out before the next occurrence of
DRDY or the remaining data are corrupted. It is
recommended to monitor DRDY to synchronize the
start of the read operation to avoid data corruption.
Before DRDY asserts low, the MSB of the Status byte
or the MSB of the data are output on DOUT (CS =
'0'), as shown in Figure 44. In this format, reading the
data a second time within the same DRDY frame
returns data = 0.
To read channel data in this mode (register format),
the first three bits of the command byte to be shifted
into the device are 001. The MUL bit must be set
because this command is a multiple byte read. The
remaining bits are don’t care but must be clocked to
the device. During this time, ignore any data that
appear on DOUT until the command completes.
These data should be ignored. Beginning with the
eighth SCLK falling edge (command byte completed),
the MSB of the channel data are restarted on DOUT.
The user clocks the data on the following rising edge
of SCLK. A total of 32 SCLK transitions complete the
data read operation. Unlike the direct read mode, the
channel data can be read during a DRDY transition
without data corruption. This mode is recommended
when DRDY is not used and the data are polled to
detect for the occurrence of new data or when CS is
tied low to avoid the necessity for an SPI timeout that
otherwise occurs when reading data directly. This
option avoids conflicts with DRDY, as shown in
Figure 45.
COMMAND DESCRIPTION
Commands may be sent to the ADS1158 with CS tied
low. However, after the Channel Data Read Direct
operation, it is necessary to toggle CS or an SPI
timeout must occur to reset the interface before
sending a command.
DRDY
CS
(1)
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
SCLK
(2)
DOUT
Data Byte 1 (MSB)
Status Byte
Data Byte 2 (LSB)
DIN
(hold inactive)
(3)
(1) No SCLK activity.
(2) Optional for Auto-Scan mode, disabled for Fixed-Channel mode. See Table 12, Status Byte.
(3) After the channel data read operation, CS must be toggled or an SPI timeout must occur before sending commands.
Figure 44. Channel Data Read Direct (No Command)
CS
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
SCLK
DIN
DOUT
Command Byte 1
Don't Care
Don't Care
Data
(2)
Don't Care
Data
(1)
(2)
(1) After the prescribed number of registers are read, then one or more additional commands can be issued in succession.
(2) Three bytes for channel data register read. See Table 12, Status Byte. One or more bytes for register read, depending on MUL bit.
Figure 45. Register and Channel Data (Register Format) Read
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Register Read Command
Beginning with the eighth SCLK rising edge
(command byte completed), the MSB of the data are
shifted in. The remaining seven SCLK rising edges
complete the write to a single register. If MUL = '1',
the data to the next register can be written by
supplying additional SCLKs. The operation terminates
when the last register is accessed (address = 09h),
as shown in Figure 46.
To read register data, the first three bits of the
command byte to be shifted into the device are 010.
These bits are followed by the multiple register read
bit (MUL). If MUL = '1', then multiple registers can be
read in sequence beyond the desired register. If
MUL = '0', only data from the addressed register can
be read. The last four bits of the command word are
the beginning register address bits. During this time,
the invalid data may appear on DOUT until the
command is completed. These data should be
ignored. Beginning with the eighth falling edge of
SCLK (command byte completed), the MSB of the
register data are output on DOUT. The remaining
eight SCLK transitions complete the read of a single
register. If MUL = '1', the data from the next register
can be read in sequence by supplying additional
SCLKs. The operation terminates when the last
register is accessed (address = 09h); see Figure 45.
CONTROL COMMANDS
Pulse Convert Command
See Conversion Control section.
Reset Command
The Reset command resets the ADC. All registers
are reset to their default values. A conversion in
process continues but will be invalid when completed
(DRDY low). This conversion data should be
discarded. Note that the SPI interface may require
reset for this command, or any command, to function.
To ensure device reset under a possible locked SPI
interface condition, do one of the following: 1) toggle
CS high then low and send the reset command; or 2)
hold SCLK inactive for 256/fCLK or 4096/fCLK and send
the reset command. The control commands are
illustrated in Figure 47.
Register Write Command
To write register data, the first three bits of the
command byte to be shifted into the device are 011.
These bits are followed by the multiple register read
bit (MUL). If MUL = '1', then multiple registers can be
written in sequence beyond the desired register. If
MUL = '0', only data to the addressed register can be
written. The remaining four bits of the command word
are the beginning register address bits. During this
time, the invalid data may appear on DOUT until the
command is completed. These data should be
ignored.
CS
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
SCLK
Command Byte
DIN
Register Data
(1)
Register Data
(1)(2)
(1) One or more bytes, depending on MUL bit.
(2) After the prescribed number of registers are read, then one or more additional commands can be issued in succession.
Figure 46. Register Write Operation
CS
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
SCLK
DIN
Command 1
Command 2
(1)
Command 3
(1)
(1) One or more additional commands can be issued in succession.
Figure 47. Control Command Operation
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CHANNEL DATA
The data read operation outputs either three bytes (one byte for status and two bytes for data), or two bytes for
data only. The selection of the 3-byte or 2-byte data read is set by the bit STAT in register CONFIG0 (see
Table 12, Status Byte, for options). In the 3-byte read, the first byte is the status byte and the following two bytes
are the data bytes. The MSB (Data15) of the data are shifted out first.
Table 9. CHANNEL DATA FORMAT
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
1
BYTE
STATUS
NEW
OVF
SUPPLY
CHID4
CHID3
CHID2
CHID1
CHID0
2
MSB
Data15
Data14
Data13
Data12
Data11
Data10
Data9
Data8
3
LSB
Data7
Data6
Data5
Data4
Data3
Data2
Data1
Data0
STATUS BYTE
BIT STATUS.7, NEW
The NEW bit is set when the results of a Channel Data Read Command returns new channel data. The bit
remains set indefinitely until the channel data are read. When the channel data are read again before the
converter updates with new data, the previous data are output and the NEW bit is cleared. If the channel data
are not read before the next conversion update, the data from the previous conversion is lost. As shown in
Figure 48, the NEW bit emulates the operation of the DRDY output pin. To emulate the function of the DRDY
output pin in software, the user reads data at a rate faster than the converter data rate. The user then polls the
NEW bit to detect for new channel data.
0 = Channel data have not been updated since the last read operation.
1 = Channel data have been updated since the last read operation.
DRDY
NEW Bit
Data Reads
(register format)
Figure 48. NEW Bit Operation
BIT STATUS.6, OVF
When this bit is set, it indicates that the differential voltage applied to the ADC inputs have exceeded the range
of the converter |VIN| > 1.06VREF. During over-range, the output code of the converter clips to either positive FS
(VIN ≥ 1.06 × VREF) or negative FS (VIN ≤ –1.06 × VREF). This bit, with the MSB of the data, can be used to
detect positive or negative over-range conditions. Note that because of averaging incorporated within the digital
filter, the absence of this bit does not assure that the modulator of the ADC has not saturated as a result of
possible transient input overload conditions.
BIT STATUS.5, SUPPLY
This bit indicates that the analog power-supply voltage (AVDD – AVSS) is below a preset limit. The SUPPLY bit
is set when the value falls below 4.3V (typically) and is reset when the value rises 50mV higher (typically) than
the lower trip point. The output data of the ADC may not be valid under low power-supply conditions.
BITS CHID[4:0] CHANNEL ID BITS
The Channel ID bits indicate the measurement channel of the acquired data. Note that for Fixed-Channel mode,
the Channel ID bits are undefined. See Table 10 for the channel ID, the measurement priority, and the channel
description for Auto-Scan Mode.
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BITS DATA[15:0] OF DATA BYTES
The ADC output data are 16 bits wide (DATA[15:0]). DATA15 is the most significant bit (MSB) and DATA0 is the
least significant bit (LSB). The data are coded in binary twos complement (BTC) format.
Table 10. Channel ID and Measurement Order (Auto-Scan Mode)
32
BITS CHID[4:0]
PRIORITY
CHANNEL
DESCRIPTION
00h
1 (highest)
DIFF0 (AIN0–AIN1)
Differential 0
01h
2
DIFF1 (AIN2–AIN3)
Differential 1
02h
3
DIFF2 (AIN4–AIN5)
Differential 2
03h
4
DIFF3 (AIN6–AIN7)
Differential 3
04h
5
DIFF4 (AIN8– AIN9)
Differential 4
05h
6
DIFF5 (AIN10–AIN11)
Differential 5
06h
7
DIFF6 (AIN12–AIN13)
Differential 6
07h
8
DIFF7 (AIN14–AIN15)
Differential 7
08h
9
AIN0
Single-ended 0
09h
10
AIN1
Single-ended 1
0Ah
11
AIN2
Single-ended 2
0Bh
12
AIN3
Single-ended 3
0Ch
13
AIN4
Single-ended 4
0Dh
14
AIN5
Single-ended 5
0Eh
15
AIN6
Single-ended 6
0Fh
16
AIN7
Single-ended 7
10h
17
AIN8
Single-ended 8
11h
18
AIN9
Single-ended 9
12h
19
AIN10
Single-ended 10
13h
20
AIN11
Single-ended 11
14h
21
AIN12
Single-ended 12
15h
22
AIN13
Single-ended 13
16h
23
AIN14
Single-ended 14
17h
24
AIN15
Single-ended 15
18h
25
OFFSET
Offset
1Ah
26
VCC
AVDD – AVSS supplies
Temperature
1Bh
27
TEMP
1Ch
28
GAIN
Gain
1Dh
29 (lowest)
REF
External reference
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COMMAND AND REGISTER DEFINITIONS
Commands are used to read channel data, access the configuration registers, and control the conversion
process. If the command is a register read or write operation, one or more data bytes follow the command byte.
If bit MUL = 1 in the command byte, then multiple registers can be read or written in one command operation
(see the MUL bit). Commands can be sent back-to-back without toggling CS; however, after a channel Data
Read Direct operation, CS must be toggled or an SPI timeout must occur before sending a command. The data
read by command does not require CS to be toggled.
The command byte consists of three fields: the Command Bits (C[2:0]), multiple register access bit (MUL), and
the Register Address Bits (A[3:0]); see the Command Byte register.
Command Byte
7
6
5
4
3
2
1
0
C2
C1
C0
MUL
A3
A2
A1
A0
Bits C[2:0]—Command Bits
These bits code the command within the command byte.
C[2:0]
DESCRIPTION
COMMENTS
000
Channel data read direct (no command)
001
Channel data read command (register format)
010
Register read command
011
Register write command
100
Pulse convert command
101
Reserved
110
Reset command
111
Channel data read direct (no command)
Toggle CS or allow SPI timeout before sending command
Set MUL = 1; status byte always included in data
A[3:0] = 0000
MUL, A[3:0] are don't care
MUL, A[3:0] don't care
Toggle CS or allow SPI timeout before sending command
Bit 4 MUL: Multiple Register Access
0 = Disable Multiple Register Access
1 = Enable Multiple Register Access
This bit enables the multiple register access. This option allows writing or reading more than one register in a
single command operation. If only one register is to be read or written, set MUL = '0'. For multiple register
access, set MUL = '1'. The read or write operation begins at the addressed register. The ADS1158 automatically
increments the register address for each register data byte subsequently read or written. The multiple register
read or write operations complete after register address = 09h (device ID register) has been accessed.
The multiple register access is terminated in one of three ways:
1. The user takes CS high. This action resets the SPI interface.
2. The user holds SCLK inactive for 4096 fCLK cycles. This action resets the SPI interface.
3. Register address = 09h has been accessed. This completes the command and the ADS1158 is then ready
for a new command. Note for the Channel Data Read command, this bit must be set to read the three data
bytes (one status byte and two data bytes).
A[3:0] Register Address Bits
These bits are the register addresses for a register read or write operation; see Table 11.
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REGISTERS
Table 11. Register Map
ADDRESS
Bits A[3:0]
REGISTER
NAME
DEFAULT
VALUE
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
00h
CONFIG0
0Ah
0
SPIRST
MUXMOD
BYPAS
CLKENB
CHOP
STAT
0
01h
CONFIG1
83h
IDLMOD
DLY2
DLY1
DLY0
SBCS1
SBCS0
DRATE1
DRATE0
02h
MUXSCH
00h
AINP3
AINP2
AINP1
AINP0
AINN3
AINN2
AINN1
AINN0
03h
MUXDIF
00h
DIFF7
DIFF6
DIFF5
DIFF4
DIFF3
DIFF2
DIFF1
DIFF0
04h
MUXSG0
FFh
AIN7
AIN6
AIN5
AIN4
AIN3
AIN2
AIN1
AIN0
05h
MUXSG1
FFh
AIN15
AIN14
AIN13
AIN12
AIN11
AIN10
AIN9
AIN8
06h
SYSRED
00h
0
0
REF
GAIN
TEMP
VCC
0
OFFSET
07h
GPIOC
FFh
CIO7
CIO6
CIO5
CIO4
CIO3
CIO2
CIO1
CIO0
08h
GPIOD
00h
DIO7
DIO6
DIO5
DIO4
DIO3
DIO2
DIO1
DIO0
09h
ID
9Bh
ID7
ID6
ID5
ID4
ID3
ID2
ID1
ID0
CONFIG0: CONFIGURATION REGISTER 0 (Address = 00h)
7
6
5
4
3
2
1
0
0
SPIRST
MUXMOD
BYPAS
CLKENB
CHOP
STAT
0
Default = 0Ah.
Bit 7
Must be 0 (default)
Bit 6
SPIRST SPI Interface Reset Timer
This bit sets the number of fCLK cycles in which SCLK is inactive until the SPI interface resets. This bit
places a lower limit on the frequency of SCLK in which to read or write data to the device. The SPI
interface only is reset and not the device itself. When the SPI interface is reset, it is ready for a new
command.
0 = Reset when SCLK inactive for 4096fCLK cycles (256µs, fCLK = 16MHz) (default).
1 = Reset when SCLK inactive for 256fCLK cycles (16µs, fCLK = 16MHz).
Bit 5
MUXMOD
This bit sets either the Auto-Scan or Fixed-Channel mode of operation.
0 = Auto-Scan mode (default)
In Auto-Scan mode, the input channel selections are eight differential channels (DIFF0–DIFF7) and 16
single-ended channels (AIN0–AIN15). Additionally, five internal monitor readings can be selected.
These selections are made in registers MUXDIF, MUXSG0, MUXSG1, and SYSRED. In this mode,
settings in register MUXSCH have no effect. See the Auto-Scan Mode section for more details.
1 = Fixed-Channel mode
In Fixed-Channel mode, any of the analog input channels may be selected for the positive
measurement and the negative measurement channels. The inputs are selected in register MUXSCH.
In this mode, registers MUXDIF, MUXSG0, MUXSG1, and SYSRED have no effect. Note that it is not
possible to select the internal monitor readings in this mode.
Bit 4
BYPAS
This bit selects either the internal or external connection from the multiplexer output to the ADC input.
0 = ADC inputs use internal multiplexer connection (default).
1 = ADC inputs use external ADC inputs (ADCINP and ADCINN).
Note that the Temperature, VCC, Gain, and Reference internal monitor readings automatically use the
internal connection, regardless of the BYPAS setting. The Offset reading uses the setting of BYPAS.
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Bit 3
CLKENB
This bit enables the clock output on pin CLKIO. The clock output originates from the device crystal
oscillator and PLL circuit.
0 = Clock output on CLKIO disabled.
1 = Clock output on CLKIO enabled (default).
Note: If the CLKSEL pin is set to '1', the CLKIO pin is a clock input only. In this case, setting this bit
has no effect.
Bit 2
CHOP
This bit enables the chopping feature on the external multiplexer loop.
0 = Chopping disabled (default)
1 = Chopping enabled
The chopping feature corrects for offset originating from components used in the external multiplexer
loop; see the External Chopping section.
Note that for Internal System readings (Temperature, VCC, Gain, and Reference), the CHOP bit must
be 0.
Bit 1
STAT Status Byte Enable
When reading channel data from the ADS1158, a status byte is normally included with the conversion
data. However, in some ADS1158 operating modes, the status byte can be disabled. Table 12, Status
Byte, shows the modes of operation and the data read formats in which the status byte can be
disabled.
0 = Status byte disabled
1 = Status byte enabled (default)
Bit 0
Must be 0
Table 12. Status Byte
CHANNEL DATA
READ COMMAND
CHANNEL DATA
READ DIRECT
Auto-Scan
Always enabled
Enabled/disabled by STAT bit
Fixed-Channel
Always enabled (byte is undefined)
Always disabled
MODE
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CONFIG1: CONFIGURATION REGISTER 1 (Address = 01h)
7
6
5
4
3
2
1
0
IDLMOD
DLY2
DLY1
DLY0
SBCS1
SBCS0
DRATE1
DRATE0
Default = 83h.
Bit 7
IDLMOD
This bit selects the Idle mode when the device is not converting, Standby or Sleep. The Sleep mode
offers lower power consumption but has a longer wake-up time to re-enter the run mode; see the Idle
Modes section.
0 = Select standby mode
1 = Select sleep mode (default)
Bits
6–4
DLY[2:0]
These bits set the amount of time the converter delays after indexing to a new channel but before
starting a new conversion. This value should be set large enough to allow for the full settling of
external filtering or buffering circuits used between the MUXOUTP, MUXOUTN, and ADCINP,
ADCINN pins; see the Switch Time Delay section. (default = 000)
Bits
3–2
SBCS[1:0]
These bits set the sensor bias current source.
0 = Sensor bias current source off (default)
1 = 1.5µA source
3 = 24µA source
Bits
1–0
DRATE[1:0]
These bits set the data rate of the converter. Slower reading rates yield increased resolution. The
actual data rates shown in the table can be slower, depending on the use of Switch Time Delay or the
Chop feature. See the Switch Time Delay section. The reading rate scales with the master clock
frequency.
DRATE[1:0]
DATA RATE
AUTO-SCAN MODE
(SPS)
DATA RATE
FIXED-CHANNEL MODE
(SPS)
11
23739
125000
10
15123
31250
01
6168
7813
00
1831
1953
fCLK = 16MHz, Chop = 0, Delay = 0.
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MUXSCH: MULTIPLEXER FIXED-CHANNEL REGISTER (Address = 02h)
7
6
5
4
3
2
1
0
AINP3
AINP2
AINP1
AINP0
AINN3
AINN2
AINN1
AINN0
Default = 00h.
This register selects the input channels of the multiplexer to be used for the Fixed-Channel mode. The MUXMOD
bit in register CONFIG0 must be set to '1'. In this mode, bits AINN[3:0] select the analog input channel for the
negative ADC input, and bits AINP[3:0] select the analog input channel for the positive ADC input. See the
Fixed-Channel Mode section.
MUXDIF: MULTIPLEXER DIFFERENTIAL INPUT SELECT REGISTER (Address = 03h)
7
6
5
4
3
2
1
0
DIFF7
DIFF6
DIFF5
DIFF4
DIFF3
DIFF2
DIFF1
DIFF0
Default = 00h.
MUXSG0: MULTIPLEXER SINGLE-ENDED INPUT SELECT REGISTER 0 (Address = 04h)
7
6
5
4
3
2
1
0
AIN7
AIN6
AIN5
AIN4
AIN3
AIN2
AIN1
AIN0
Default = FFh.
MUXSG1: MULTIPLEXER SINGLE-ENDED INPUT SELECT REGISTER 1 (Address = 05h)
7
6
5
4
3
2
1
0
AIN15
AIN14
AIN13
AIN12
AIN11
AIN10
AIN9
AIN8
Default = FFh.
SYSRED: SYSTEM READING SELECT REGISTER (Address = 06h)
7
6
5
4
3
2
1
0
0
0
REF
GAIN
TEMP
VCC
0
OFFSET
Default = 00h.
These four registers select the input channels and the internal readings for measurement in Auto-Scan mode.
For differential channel selections (DIFF0…DIFF7), adjacent input pins (AIN0/AIN1, AIN2/AIN3, etc.) are pre-set
as differential inputs. All single-ended inputs are measured with respect to the AINCOM input. AINCOM may be
set to any level within ±100mV of the analog supply range. Channels not selected are skipped in the
measurement sequence. Writing to any of these four registers resets the internal channel pointer to the channel
with the highest priority (see Table 10). Note that the bits indicated as '0' must be set to 0.
0 = Channel not selected within a reading sequence.
1 = Channel selected within a reading sequence.
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GPIOC: GPIO CONFIGURATION REGISTER (Address = 07h)
7
6
5
4
3
2
1
0
CIO7
CIO6
CIO5
CIO4
CIO3
CIO2
CIO1
CIO0
Default = FFh.
This register configures the GPIO pins as inputs or as outputs. Note that the default configurations of the port
pins are inputs and as such they should not be left floating. See the GPIO Digital Port section.
0 = GPIO is an output; 1 = GPIO is an input (default).
CIO[7:0] GPIO Configuration
bit
bit
bit
bit
bit
bit
bit
bit
7
6
5
4
3
2
1
0
CIO7,
CIO6,
CIO5,
CIO4,
CIO3,
CIO2,
CIO1,
CIO0,
digital
digital
digital
digital
digital
digital
digital
digital
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
configuration bit
configuration bit
configuration bit
configuration bit
configuration bit
configuration bit
configuration bit
configuration bit
for
for
for
for
for
for
for
for
pin GPIO7
pin GPIO6
pin GPIO5
pin GPIO4
pin GPIO3
pin GPIO2
pin GPIO1
pin GPIO0
GPIOD: GPIO DATA REGISTER (Address = 08h)
7
6
5
4
3
2
1
0
DIO7
DIO6
DIO5
DIO4
DIO3
DIO2
DIO1
DIO0
Default = 00h.
This register is used to read and write data to the GPIO port pins. When reading this register, the data returned
corresponds to the state of the GPIO external pins, whether they are programmed as inputs or as outputs. As
outputs, a write to the GPIOD sets the output value. As inputs, a write to the GPIOD has no effect. See the
GPIO Digital Port section.
0 = GPIO is logic low (default); 1 = GPIO is logic high.
DIO[7:0] GPIO Data
bit
bit
bit
bit
bit
bit
bit
bit
7
6
5
4
3
2
1
0
DIO7,
DIO6,
DIO5,
DIO4,
DIO3,
DIO2,
DIO1,
DIO0,
digital
digital
digital
digital
digital
digital
digital
digital
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
data
data
data
data
data
data
data
data
bit
bit
bit
bit
bit
bit
bit
bit
for pin
for pin
for pin
for pin
for pin
for pin
for pin
for pin
GPIO7
GPIO6
GPIO5
GPIO4
GPIO3
GPIO2
GPIO1
GPIO0
ID: DEVICE ID REGISTER (Address = 09h)
7
6
5
4
3
2
1
0
ID7
ID6
ID5
ID4
ID3
ID2
ID1
ID0
Default = 9Bh.
NOTE: Except for bit ID4, the ID byte can change at any time without notice.
ID[7:0] ID bits
Factory-programmed ID bits. Read-only.
Bit 4
38
ID4
0 = ADS1258 (24-bit ADC)
1 = ADS1158 (16-bit ADC)
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APPLICATION INFORMATION
HARDWARE CONSIDERATIONS
The following summarizes the design and layout
considerations when using the ADS1158:
a. Power Supplies: The converter accepts a single
+5V supply (AVDD = +5V and AVSS = AGND) or
dual, bipolar supplies (typically AVDD = +2.5V,
AVSS = –2.5V). Dual supply operation
accommodates true bipolar input signals, within a
±2.5V range. Note that the maximum negative
input voltage to the multiplexer is limited to
AVSS – 100mV, and the maximum positive input
voltage is limited to AVDD + 100mV. The range
for the digital power supply (DVDD) is 2.7V to
5.25V. For all supplies, use a 10μF tantalum
capacitor, bypassed with a 0.1μF ceramic
capacitor, placed close to the device pins.
Alternatively, a single 10μF ceramic capacitor can
be used. The supplies should be relatively free
from noise and should not be shared with devices
that produce voltage spikes (such as relays, LED
display drivers, etc.). If a switching power supply
is used, the voltage ripple should be low (< 2mV).
The analog and digital power supplies may be
sequenced in any order.
b. Analog (Multiplexer) Inputs: The 16-channel
analog input multiplexer can accommodate 16
single-ended inputs, eight differential input pairs,
or combinations of either. These options permit
freedom in choosing the input channels. The
channels do not have to be used consecutively.
Unassigned channels are skipped by the device.
In the Fixed-Channel mode, any of the analog
inputs (AIN0 to AIN15) can be addressed for the
positive input and for the negative input. The
full-scale range of the device is 2.13VREF, but the
absolute analog input voltage is limited to 100mV
beyond the analog supply rails. Input signals
exceeding the analog supply rails (for example,
±10V) must be divided prior to the multiplexer
inputs.
c. Input Overload Protection: Overdriving the
multiplexer inputs may affect the conversions of
other channels. In the case of input overload,
external Schottky diode clamps and series
resistor are recommended, as shown in
Figure 49.
AVDD
BAT54SWTI
10kW
Input
AINx
typ.
AVSS
Figure 49. Input Overload Protection
d. ADC Inputs: The external multiplexer loop of the
ADS1158 allows for the inclusion of signal
conditioning between the output of the multiplexer
and the input of the ADC. Typically, an amplifier
provides gain, buffering, and/or filtering to the
input signal. For best performance, the ADC
inputs should be driven differentially. A differential
in/differential out or a single-ended-to-differential
driver is recommended. If the driver uses higher
supply voltages than the device itself (for
example, ±15V), attention should be paid to
power-supply
sequencing
and
potential
over-voltage fault conditions. Protection resistors
and/or external clamp diodes may be used to
protect the ADC inputs. A 1nF or higher capacitor
should be used directly across the ADC inputs.
e. Reference Inputs: It is recommended to use a
10μF tantalum capacitor with a 0.1μF ceramic
capacitor directly across the reference pins,
VREFP and VREFN. The reference inputs should
be driven by a low-impedance source. For rated
performance, the reference should have less than
3μVRMS broadband noise. For references with
higher noise, external filtering may be necessary.
Note that when exiting the sleep mode, the
device begins to draw a small current through the
reference pins. Under this condition, the transient
response of the reference driver should be fast
enough to settle completely before the first
reading is taken, or simply discard the first
several readings.
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f. Clock Source: The ADS1158 requires a clock
signal for operation. The clock can originate from
either the crystal oscillator or from an external
clock source. The internal oscillator uses a PLL
circuit and an external 32.768kHz crystal to
generate a 15.7MHz master clock. The PLL
requires a 22nF capacitor from the PLLCAP pin
to AVSS. The crystal and load capacitors should
be placed close to the pins as possible and kept
away from other traces with ac components. A
buffered output of the 15.7MHz clock can be
used to drive other converters or controllers. An
external clock source can be used up to 16MHz.
For best performance, the clock of the SPI
interface controller and the converter itself should
be on the same domain. This configuration
requires that the ratio of the SCLK to device clock
must be limited to 1,1/2,1/4, 1/8, etc.
g. Digital Inputs: It is recommended to source
terminate the digital inputs and outputs of the
device with a 50Ω (typical) series resistor. The
resistors should be placed close to the driving
end of the source (output pins, oscillator, logic
gates, DSP, etc). This placement helps to reduce
the ringing and overshoot on the digital lines.
h. Hardware Pins: START, DRDY, RESET, and
PWDN. These pins allow direct pin control of the
ADS1158. The equivalent of the START and
DRDY pins is provided via commands through
the SPI interface; these pins may be left unused.
The device also has a RESET command. The
PWDN pin places the ADC into very low-power
state
where
the
device
is
inactive.
i. SPI Interface: The ADS1158 has an
SPI-compatible interface. This interface consists
of four signal lines: SCLK, DIN, DOUT, and CS.
When CS is high, the DIN input is ignored and
the DOUT output 3-states. See Chip Select
(CS
) for more details. The SPI
interface can be operated in a minimum
configuration without the use of CS (tie CS low;
see the Serial Interface and Communication
Protocol sections).
j. GPIO: The ADS1158 has eight, userprogrammable digital I/O pins. These pins are
controlled by register settings. The register
setting is default to inputs. If these pins are not
used, tie them high or low (do not float input pins)
or configure them as outputs.
k. QFN Package: See Application Note SLUA271,
40
QFN/SON PCB Attachment for PCB layout
recommendations, available for download at
www.ti.com. The exposed thermal pad of the
ADS1158 should be connected electrically to
AVSS.
CONFIGURATION GUIDE
Configuration of the ADS1158 involves setting the
configuration registers via the SPI interface. After the
device is configured for operation, channel data are
read from the device through the same SPI interface.
The following procedure is recommended to configure
the device:
1. Reset the SPI Interface: Before using the SPI
interface, it may be necessary to recover the SPI
interface. To reset the interface, set CS high or
disable SCLK for 4096 (256) fCLK cycles.
2. Stop the Converter: Set the START pin low to
stop the converter. Although not necessary for
configuration, this command stops the channel
scanning sequence which then points to the first
channel after configuration.
3. Reset the Converter: The reset pin can be
pulsed low or a Reset command can be sent.
Although not necessary for configuration, reset
re-initializes the device into a known state.
4. Configure the Registers: The registers are
configured by writing to them either sequentially
or as a group. The user may configure the
software in either mode. Any write to the
Auto-Scan channel-select registers resets the
channel pointer to the channel of highest priority.
5. Verify Register Data: The register data may be
read
back
for
verification
of
device
communications.
6. Start the Converter: The converter can be
started with the START pin or with a Pulse
Convert command sent through the interface.
7. Read Channel Data: The DRDY asserts low
when data are ready. The channel data can be
read at that time. If DRDY is not used, the
updated channel data can be checked by reading
the NEW bit in the status byte. The status byte
also indicates the origin of the channel data. If
the data for a given channel is not read before
DRDY asserts low again, the data for that
channel is lost and replaced with new channel
data.
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DIGITAL INTERFACE CONNECTIONS
The ADS1158 SPI-compatible interface easily
connects to a wide variety of microcontrollers and
DSPs. Figure 50 shows the basic connection to TI's
MSP430 family of low-power microcontrollers.
Figure 51 shows the connection to microcontrollers
with an SPI interface such as the 68HC11 family, or
TI's MSC12xx family. Note that the MSC12xx
includes a high-resolution ADC; the ADS1158 can be
used to provide additional channels of measurement
or add higher-speed connections. Finally, Figure 52
shows how to connect the ADS1158 to a TMS320x
DSP.
TMS320R2811
ADS1158
DIN
SPISIMO
DOUT
SPISOMI
DRDY
XINT1
SCLK
SPICLK
(1)
SPISTA
CS
(1) CS may be tied low.
Figure 52. Connection to TMS320R2811 DSP
ADS1158
MSP430
GPIO Connections
DIN
P1.3
DOUT
P1.2
DRDY
P1.0
SCLK
P1.6
(1)
P1.4
CS
The ADS1158 has eight GPIO pins. Each pin can be
configured as an input or an output. Note that pins
configured as inputs should not float. The pins can be
used to read key pads, drive LED indicator, etc., by
reading and writing the GPIO data register (GPIOD).
See Figure 53.
3.3V
(1) CS may be tied low.
10kW
Figure 50. Connection to MSP430 Microcontroller
ADS1158
MSC12xx or
68HC11
DIN
MOSI
DOUT
MISO
DRDY
INT
SCLK
SCK
CS
(1)
GPIOx
(Input)
Key Pad
3.3V
LED Indicator
ADS1158
470
GPIOx
(Output)
4.7kW
IO
Figure 53. GPIO Connections
(1) CS may be tied low.
Figure 51. Connection to Microcontrollers with an
SPI Interface
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ADS1158
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ANALOG INPUT CONNECTIONS
Figure 54 shows the ADS1158 interfacing to
high-level ±10V inputs, commonly used in industrial
environments. In this case, bipolar power supplies are
used to avoid the need for input signal level-shifting
that is otherwise required with a single supply. The
input resistors serve both to reduce the level of the
10V input signal to within the ADC range and also
protect the inputs from inadvertent signal over-voltage
up to 30V. The external amplifiers convert the
single-ended inputs to a fully differential output to
drive the ADC inputs. Driving the inputs differentially
maintains good linearity performance. The 2.2nF
capacitor at the ADC inputs is required to bypass the
ADC sampling currents. The 2.5V reference,
REF3125, is filtered and buffered to provide a
low-noise reference input to the ADC. The chop
feature of the ADC can be used to reduce offset and
offset drift of the amplifiers.
For ±1V input signals, the input resistor divider can
be removed and replaced with a series protection
resistor. For 20mA input signals, the input resistor
divider is replaced by a 50Ω resistor, connected from
each input to AINCOM.
+
10mF
Figure 55 illustrates the ADS1158 interfacing to
multiple pressure sensors that have a resistor bridge
output. Each sensor is excited by the +5V single
supply that also powers the ADS1158, and likewise is
used as the ADS1158 reference input; the 6% input
overrange capability accommodates input levels at or
above VREF. The ratiometric connection provides
cancellation of excitation voltage drift and noise. For
best performance, the +5V supply should be free
from glitches or transients. The 5V supply input
amplifiers (two OPA365s) form a differential
input/differential output buffer with the gain set to 10.
The chop feature of the ADS1158 is used to reduce
offset and offset drift to very low levels. The 2.2nF
capacitor at the ADC inputs is required to bypass the
ADC sampling currents. The 47Ω resistors isolate the
operational amplifier outputs from the filter capacitor.
+2.5V
-2.5V
0.1mF
When using Auto-Scan mode to sequence through
the channels, the switch time delay feature
(programmable by registers) can be used to provide
additional settling time of the external components.
+
0.1mF
10mF
+2.5V
+2.5V
AVSS
AVDD
9.09kW
OPA350
AIN0
¼
1kW
AINCOM
+
10kW
10mF
+
-2.5V
0.47mF
100mF
0.1mF
REFN
ADCINN
AIN15
ADCINP
9.09kW
±10V
100W
REF5040
0.1mF
ADS1158
MUXOUTN
¼
1kW
REFP
MUXOUTP
±10V
-2.5V
2.2nF
47W
+2.5V
10kW
20mA Input
AINx
10kW
OPA365
+2.5V
50W
47W
-2.5V
OPA365
-2.5V
NOTE: 0.1μF capacitors not shown.
Figure 54. Multichannel, ±10V Single-Ended Input, Bipolar Supply Operation
42
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+5V
RFI
+
0.1mF
10mF
2kW
RFI
AVSS
AIN0
AVDD
2kW
RFI
REFP
AIN1
RFI
10mF
¼
¼
REFN
ADCINN
AINCOM
ADCINP
AIN15
MUXOUTP
AIN14
2kW
RFI
0.1mF
ADS1158
MUXOUTN
¼
2kW
+
RFI
+5V
2.2nF
47W
OPA365
R2
10kW
R1
2.2kW
R2
10kW
47W
OPA365
NOTE: G = 1 + 2R2/R1. 0.1μF supply bypass capacitor not shown.
Figure 55. Bridge Input, Single-Supply Operation
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ADS1158
SBAS429D – JUNE 2008 – REVISED MARCH 2011
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REVISION HISTORY
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision C (November, 2010) to Revision D
Page
•
Changed default value for ID Register in Table 11 ............................................................................................................ 34
•
Revised description of Device ID Register ......................................................................................................................... 38
Changes from Revision B (September, 2008) to Revision C
Page
•
Added footnotes to temperature sensor reading parameter; added second maximum value for coefficient condition
specification .......................................................................................................................................................................... 3
•
Updated Figure 13 ................................................................................................................................................................ 9
•
Listed additional crystal recommendations in Table 2 ........................................................................................................ 15
•
Changed Equation 8 ........................................................................................................................................................... 24
44
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Product Folder Link(s): ADS1158
PACKAGE OPTION ADDENDUM
www.ti.com
5-Aug-2016
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
Lead/Ball Finish
MSL Peak Temp
(2)
(6)
(3)
Op Temp (°C)
Device Marking
(4/5)
ADS1158IRTCR
ACTIVE
VQFN
RTC
48
2500
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-40 to 105
ADS1158
ADS1158IRTCT
ACTIVE
VQFN
RTC
48
250
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-40 to 105
ADS1158
ADS1158IRTCTG4
ACTIVE
VQFN
RTC
48
250
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-2-260C-1 YEAR
-40 to 105
ADS1158
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(3)
MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4)
There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
(5)
Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation
of the previous line and the two combined represent the entire Device Marking for that device.
(6)
Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish
value exceeds the maximum column width.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
Addendum-Page 1
Samples
PACKAGE OPTION ADDENDUM
www.ti.com
5-Aug-2016
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
Addendum-Page 2
PACKAGE MATERIALS INFORMATION
www.ti.com
12-Feb-2019
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
Package Package Pins
Type Drawing
SPQ
Reel
Reel
A0
Diameter Width (mm)
(mm) W1 (mm)
B0
(mm)
K0
(mm)
P1
(mm)
W
Pin1
(mm) Quadrant
ADS1158IRTCR
VQFN
RTC
48
2500
330.0
16.4
7.3
7.3
1.5
12.0
16.0
Q2
ADS1158IRTCT
VQFN
RTC
48
250
180.0
16.4
7.3
7.3
1.5
12.0
16.0
Q2
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
12-Feb-2019
*All dimensions are nominal
Device
Package Type
Package Drawing
Pins
SPQ
Length (mm)
Width (mm)
Height (mm)
ADS1158IRTCR
VQFN
RTC
48
2500
350.0
350.0
43.0
ADS1158IRTCT
VQFN
RTC
48
250
213.0
191.0
55.0
Pack Materials-Page 2
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