Texas Instruments | Octal Current Input, 20-Bit Analog-to-Digital Converter (Rev. B) | Datasheet | Texas Instruments Octal Current Input, 20-Bit Analog-to-Digital Converter (Rev. B) Datasheet

Texas Instruments Octal Current Input, 20-Bit Analog-to-Digital Converter (Rev. B) Datasheet
DDC118
SBAS325B − JUNE 2004 − REVISED APRIL 2009
Octal Current Input, 20-Bit
Analog-To-Digital Converter
FEATURES
D
D
D
D
D
D
D
D
APPLICATIONS
SINGLE-CHIP SOLUTION TO DIRECTLY
MEASURE EIGHT LOW-LEVEL CURRENTS
HIGH PRECISION, TRUE INTEGRATING
FUNCTION
INTEGRAL LINEARITY:
±0.01% of Reading ±0.5ppm of FSR
VERY LOW NOISE: 5.2ppm of FSR
LOW POWER: 13.5mW/channel
ADJUSTABLE DATA RATE: Up to 3.125kSPS
PROGRAMMABLE FULL SCALE
DAISY-CHAINABLE SERIAL INTERFACE
AVDD
VREF
DVDD
CLK
CONV
IN1
RANGE0
Dual
Switched
Integrator
∆Σ
Modulator
Digital
Filter
RANGE1
Control
RANGE2
TEST
CLK_4X
IN3
HISPD/LOPWR
Dual
Switched
Integrator
RESET
IN2
Dual
Switched
Integrator
∆Σ
Modulator
Digital
Filter
FORMAT
D
D
D
D
CT SCANNER DAS
PHOTODIODE SENSORS
INFRARED PYROMETERS
LIQUID/GAS CHROMATOGRAPHY
Protected by US Patent #5841310
DESCRIPTION
The DDC118 is a 20-bit, octal channel, current-input
analog-to-digital (A/D) converter. It combines both
current-to-voltage and A/D conversion so that eight
low-level current output devices, such as photodiodes, can
be directly connected to its inputs and digitized.
For each of the eight inputs, the DDC118 provides a
dual-switched integrator front-end. This design allows for
continuous current integration: while one integrator is
being digitized by the onboard A/D converter, the other is
integrating the input current. Adjustable full-scale ranges
from 12pC to 350pC and adjustable integration times from
50µs to 1s allow currents from fAs to µAs to be measured
with outstanding precision. Low-level linearity is ±0.5ppm
of the full-scale range and noise is 5.2ppm of the full-scale
range.
IN4
DCLK
Dual
Switched
Integrator
DCLK
IN5
DVALID
Dual
Switched
Integrator
∆Σ
Modulator
Digital
Filter
Digital
Input/Output
DOUT
IN7
DOUT
Dual
Switched
Integrator
DIN
IN6
Dual
Switched
Integrator
∆Σ
Modulator
DIN
Digital
Filter
IN8
Dual
Switched
Integrator
AGND
DGND
Two modes of operation are provided. In Low-Power
mode, total power dissipation is only 13.5mW per channel
with a maximum data rate of 2.5kSPS. High-Speed mode
supports data rates up to 3.125kSPS with a corresponding
dissipation of 18mW per channel.
The DDC118 has a serial interface designed for
daisy-chaining in multi-device systems. Simply connect
the output of one device to the input of the next to create
the chain. Common clocking feeds all the devices in the
chain so that the digital overhead in a multi-DDC118
system is minimal.
The DDC118 is a single-supply device using a +5V analog
supply and supporting a +2.7V to +5.25V digital supply.
Operating over the industrial temperature range of −40°C
to +85°C, the DDC118 is offered in a QFN-48 package.
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.
All trademarks are the property of their respective owners.
Copyright  2002−2009, Texas Instruments Incorporated
! ! www.ti.com
""#
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SBAS325B − JUNE 2004 − REVISED APRIL 2009
ABSOLUTE MAXIMUM RATINGS(1)
Analog Input Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 750µA
AVDD to DVDD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . −0.3V to +6V
AVDD to AGND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . −0.3V to +6V
DVDD to DGND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . −0.3V to +6V
AGND to DGND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ±0.2V
VREF Input to AGND . . . . . . . . . . . . . . . . . . 2.0V to AVDD + 0.3V
Analog Input to AGND . . . . . . . . . . . . . . . . . . . . . . . −0.3V to +0.7V
Digital Input Voltage to DGND . . . . . . . . . . . −0.3V to DVDD + 0.3V
Digital Output Voltage to DGND . . . . . . . . . −0.3V to AVDD + 0.3V
Operating Temperature . . . . . . . . . . . . . . . . . . . . . . −40°C to +85°C
Storage Temperature . . . . . . . . . . . . . . . . . . . . . . . −60°C to +150°C
Junction Temperature (TJ) . . . . . . . . . . . . . . . . . . . . . . . . . . . +150°C
(1) 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.
2
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 package and ordering information, see the Package
Option Addendum located at the end of this data sheet.
""#
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SBAS325B − JUNE 2004 − REVISED APRIL 2009
ELECTRICAL CHARACTERISTICS
At TA = +25°C, AVDD = +5V, DVDD = 3V, VREF = +4.096V, Range 5 (250pC), and continuous mode operation, unless otherwise noted.
Low-Power Mode: TINT = 400µs and CLK = 4MHz; High-Speed Mode: TINT = 320µs and CLK = 4.8MHz.
Low-Power Mode
PARAMETER
TEST CONDITIONS
ANALOG INPUT RANGE
Range 0
Range 1
Range 2
Range 3
Range 4
Range 5
Range 6
Range 7
Negative Full-Scale Range
Input Current(2)
MIN
TYP
10.2
12
13.8
47.5
50
52.5
95
100
105
142.5
150
157.5
190
200
210
237.5
250
262.5
285
300
315
332.5
350
367.5
−0.4% of Positive Full-Scale Range
750
DYNAMIC CHARACTERISTICS
Data Rate
Integration Time, TINT
High-Speed Mode
MAX
Continuous Mode
Non-continuous Mode, Range 1 to 7
2.5
1,000,000
400
50
System Clock Input (CLK)
CLK_4X = 0
CLK_4X = 1
Data Clock (DCLK)
MIN
TYP
MAX
∗(1)
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
4
16
16
pC
pC
pC
pC
pC
pC
pC
pC
pC
µA
3.125
kSPS
µS
µS
4.8
19.2
MHz
MHz
MHz
∗
320
UNITS
∗
ACCURACY
Noise, Low-Level Input(3)
CSENSOR(4) = 50pF, Range 5 (250pC)
Integral Linearity Error(6)
Resolution
Input Bias Current
Range Error Match(7)
Range Sensitivity to VREF
Offset Error
Offset Error Match(7)
DC Bias Voltage(9)
Power-Supply Rejection Ratio
Internal Test Signal
Internal Test Accuracy
FORMAT = 1
FORMAT = 0
All Ranges
VREF = 4.096 ± 0.1V
Range 5 (250pC)
Low-Level Input (< 1% FSR)
at dc
5.2
6.5
±0.01% Reading ± 0.5ppm FSR, typ
±0.025% Reading ± 1.0ppm FSR, max
20
16
0.1
10
0.1
0.5
1:1
±400
±1000
±100
±0.05
±2
±25
±200
11
±10
5.5
∗
∗
7
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
∗
ppm of
FSR(5), rms
Bits
Bits
pA
% of FSR
ppm of FSR
ppm of FSR
mV
ppm of FSR/V
pC
%
PERFORMANCE OVER TEMPERATURE
Offset Drift
±0.5
±3(8)
Offset Drift Stability
±0.2
±1(8)
DC Bias Voltage Drift(9)
Input Bias Current Drift
Range Drift(10)
3
0.01
25
1(8)
REFERENCE
Voltage
Input Current(11)
TA = +25°C to +45°C
4.000
Average Value
4.096
150
4.200
∗
190
∗
ppm of
FSR/°C
ppm of FSR/
minute
µV/°C
pA/°C
ppm/°C
V
µA
(1) ∗ indicates that specification is the same as Low-Power Mode.
(2) Exceeding maximum input current specification may damage device.
(3) Input is less than 1% of full scale.
(4) C
SENSOR is the capacitance seen at the DDC118 inputs from wiring, photodiode, etc.
(5) FSR is Full-Scale Range.
(6) A best-fit line is used in measuring nonlinearity.
(7) Matching between side A and side B of the same input.
(8) Ensured by design, not production tested.
(9) Voltage produced by the DDC118 at its input which is applied to the sensor.
(10)Range drift does not include external reference drift.
(11)Input reference current decreases with increasing T
INT (see the Voltage Reference section, page 11).
(12)Data format is Straight Binary with a small offset. The number of bits in the output word is controlled by the FORMAT pin (see text).
3
""#
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SBAS325B − JUNE 2004 − REVISED APRIL 2009
ELECTRICAL CHARACTERISTICS (continued)
At TA = +25°C, AVDD = +5V, DVDD = 3V, VREF = +4.096V, Range 5 (250pC), and continuous mode operation, unless otherwise noted.
Low-Power Mode: TINT = 400µs and CLK = 4MHz; High-Speed Mode: TINT = 320µs and CLK = 4.8MHz.
Low-Power Mode
PARAMETER
DIGITAL INPUT/OUTPUT
Logic Levels
VIH
VIL
VOH
VOL
Input Current (IIN)
Data Format(12)
POWER-SUPPLY REQUIREMENTS
Analog Power-Supply Voltage (AVDD)
Digital Power-Supply Voltage (DVDD)
Supply Current
Total Analog Current
Total Digital Current
Total Power Dissipation
Total Power Dissipation per Channel
TEST CONDITIONS
IOH = −500µA
IOL = 500µA
0 < VIN < DVDD
MIN
TYP
0.8DVDD
− 0.1
DVDD − 0.4
High-Speed Mode
MAX
MIN
DVDD + 0.1
0.2DVDD
∗
∗
0.4
±10
DVDD = +3V
DVDD = +3V
DVDD = +3V
5.25
5.25
21
1
108
13.5
150
18.75
∗
∗
28
1.34
144
18
(1) ∗ indicates that specification is the same as Low-Power Mode.
(2) Exceeding maximum input current specification may damage device.
(3) Input is less than 1% of full scale.
(4) C
SENSOR is the capacitance seen at the DDC118 inputs from wiring, photodiode, etc.
(5) FSR is Full-Scale Range.
(6) A best-fit line is used in measuring nonlinearity.
(7) Matching between side A and side B of the same input.
(8) Ensured by design, not production tested.
(9) Voltage produced by the DDC118 at its input which is applied to the sensor.
(10)Range drift does not include external reference drift.
(11)Input reference current decreases with increasing T
INT (see the Voltage Reference section, page 11).
(12)Data format is Straight Binary with a small offset. The number of bits in the output word is controlled by the FORMAT pin (see text).
4
MAX
∗
∗
∗
Straight Binary
4.75
2.7
TYP
UNITS
∗
∗
V
V
V
V
µA
∗
∗
V
V
200
25
mA
mA
mW
mW
""#
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SBAS325B − JUNE 2004 − REVISED APRIL 2009
CONV
DGND
DVALID
DGND
CLK
DGND
DCLK
DCLK
DGND
48
47 46
45
44
43
42
41
40
39
38 37
QFN
DVDD
DGND
Top View
DGND
PIN CONFIGURATION
DOUT 1
36 DIN
DOUT 2
35 DIN
CLK_4X 3
34 NC
FORMAT 4
33 NC
HISPD/LOPWR 5
32 RESET
RANGE0 6
31 TEST
DDC118
16
17
18
19
20
21
22
23 24
AGND
14 15
AIN4
13
AIN1
25 AGND
AIN5
26 AGND
AGND 12
AIN2
AGND 11
AIN6
27 AVDD
AGND
VREF 10
AIN3
28 AGND
AGND
29 DGND
AGND 9
AIN7
RANGE2 8
AIN8
30 DGND
AGND
RANGE1 7
PIN DESCRIPTIONS
PIN
NUMBER
FUNCTION
DOUT
1
Digital Output
DESCRIPTION
Serial Data Output
DOUT
2
Digital Output
Serial Data Output: Complementary Signal (optional, see text on page 13)
CLK_4X
3
Digital Input
Master Clock Divider Control: 0 = divide by 1, 1 = divide by 4
FORMAT
4
Digital Input
Digital Output Word Format: 0 = 16 Bits, 1 = 20 Bits
HISPD/LOPWR
5
Digital Input
Mode Control: 0 = Low-Power, 1 = High-Speed
RANGE0
6
Digital Input
Range Control 0 (least significant bit)
RANGE1
7
Digital Input
Range Control 1
RANGE2
8
Digital Input
Range Control 2 (most significant bit)
AGND
9, 11-13, 18, 19, 24-26, 28
Analog
VREF
10
Analog Input
External Voltage Reference Input, 4.096V Nominal
AIN8
14
Analog Input
Analog Input 8
AIN7
16
Analog Input
Analog Input 7
AIN6
20
Analog Input
Analog Input 6
AIN5
22
Analog Input
Analog Input 5
AIN4
15
Analog Input
Analog Input 4
AIN3
17
Analog Input
Analog Input 3
AIN2
21
Analog Input
Analog Input 2
AIN1
23
Analog Input
Analog Input 1
AVDD
27
Analog
Analog Power Supply, 5V Nominal
DGND
29, 30, 38, 41, 43, 45, 47, 48
Digital
Digital Ground
TEST
31
Digital Input
Test Mode Control
RESET
32
Digital Input
Resets the Digital Circuitry, Active Low
NC
33, 34
—
DIN
35
Digital Input
Serial Data Input: Complementary Signal (optional, see text on page 13)
DIN
36
Digital Input
Serial Data Input
DVDD
37
Digital
DCLK
39
Digital Input
Serial Data Clock Input: Complementary Signal (optional, see text on page 13)
DCLK
40
Digital Input
Serial Data Clock Input
CLK
42
Digital Input
Master Clock Input
DVALID
44
Digital Output
CONV
46
Digital Input
Analog Ground
No connection. These pins must be left unconnected.
Digital Power Supply, 3V Nominal
Data Valid Output, Active Low
Conversion Control Input: 0 = Integrate on Side B, 1 = Integrate on Side A
5
""#
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SBAS325B − JUNE 2004 − REVISED APRIL 2009
TYPICAL CHARACTERISTICS
At TA = +25°C, characterization done with Range 5 (250pC), AVDD = +5V, DVDD = 3V, VREF = +4.096V, and Low-Power Mode: TINT = 400µs and CLK = 4MHz,
unless otherwise noted.
NOISE vs CSENSOR
NOISE vs CSENSOR
45
Noise (ppm of FSR, rms)
Noise (ppm of FSR, rms)
40
CSENSOR Range Range Range Range Range Range Range Range
(pF)
0
1
2
3
4
5
6
7
Range 1
35
0
23.6
7.3
5.2
4.4
4.2
4.0
3.8
3.7
24
30.8
10.4
6.7
5.5
4.9
4.5
4.3
4.1
50
36.3
12.3
8.2
6.5
5.6
5.1
4.8
4.4
75
41.3
14.4
8.9
7.2
6.0
5.4
5.1
4.7
15
100
46.1
16.0
10.0
8.0
6.7
5.9
5.4
5.0
10
150
57.0
18.8
11.9
9.2
7.8
6.8
6.1
5.7
200
68.1
21.7
13.5
10.2
8.6
7.6
6.8
6.4
300
89.3
27.7
16.3
12.5
10.6
9.0
8.1
7.4
500
134.0
38.9
22.4
16.6
13.5
11.7
10.4
9.5
30
25
Range 2
20
5
Range 7
0
0
100
200
300
400
500
CSENSOR (pF)
NOISE vs INPUT LEVEL
NOISE vs TINT
6
8
7
Noise (ppm of FSR, rms)
Noise (ppm of FSR, rms)
CSENSOR = 50pF
5
4
CSENSOR = 0pF
3
2
1
6
CSENSOR = 50pF
5
CSENSOR = 0pF
4
3
2
1
Range 5
Range 5
0
0
0.1
1
10
100
0
1000
10
20
TINT (ms)
50
60
70
80
90
100
2000
CSENSOR = 50pF
All Ranges
1500
12
Range 1
10
Range Drift (ppm)
Noise (ppm of FSR, rms)
40
RANGE DRIFT vs TEMPERATURE
NOISE vs TEMPERATURE
14
Range 3
Range 2
8
6
4
1000
500
0
−500
−1000
Range 7
2
−1500
0
−40
−15
10
35
Temperature (_C)
6
30
Input Level (% of Full−Scale)
60
85
−2000
−40
−15
10
35
Temperature (_ C)
60
85
""#
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SBAS325B − JUNE 2004 − REVISED APRIL 2009
TYPICAL CHARACTERISTICS (continued)
At TA = +25°C, characterization done with Range 5 (250pC), AVDD = +5V, DVDD = 3V, VREF = +4.096V, and Low-Power Mode: TINT = 400µs and CLK = 4MHz,
unless otherwise noted.
IB vs TEMPERATURE
OFFSET DRIFT vs TEMPERATURE
10
100
Offset Drift (ppm of FSR)
All Ranges
IB (pA)
1
0.1
50
0
−50
−100
0.01
25
35
45
55
65
75
25
85
35
45
55
65
75
85
Temperature (_ C)
Temperature (_ C)
ANALOG SUPPLY CURRENT vs TEMPERATURE
DIGITAL SUPPLY CURRENT vs TEMPERATURE
25
2.5
Low−Power Mode
Low−Power Mode
DVDD = 5V
2.0
Current (mA)
Current (mA)
20
15
10
5
1.5
DVDD = 3V
1.0
0.5
0
−40
0
−15
10
35
60
−40
85
−15
10
Temperature (_C)
POWER CONSUMPTION HISTOGRAM
40
85
OFFSET DRIFT HISTOGRAM AT ROOM TEMPERATURE
1000
30
Occurences
25
20
15
Range 5
Repeated measurement
of offset drift over a
one minute interval.
800
600
400
10
200
5
16.00
15.75
15.50
15.25
15.00
14.75
14.50
14.25
14.00
13.75
13.50
13.25
13.00
12.75
12.50
12.25
0
12.00
Occurences (%)
60
1200
Low−Power Mode
Data collected
from multiple lots.
35
35
Temperature (_C)
0
−1.0
−0.6
−0.2
0.2
0.6
1.0
Offset Drift (ppm of FSR/minute)
Power per Channel (mW)
7
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SBAS325B − JUNE 2004 − REVISED APRIL 2009
THEORY OF OPERATION
The block diagram of the DDC118 is shown in Figure 1.
The device contains eight identical input channels that
perform the function of current-to-voltage integration
followed by a multiplexed A/D conversion. Each input has
two integrators so that the current-to-voltage integration
can be continuous in time. The output of the sixteen
integrators are switched to four delta-sigma (∆Σ)
converters via four four-input multiplexers. With the
AVDD
VREF
DDC118 in the continuous integration mode, the output of
the integrators from one side of the inputs will be digitized
while the other eight integrators are in the integration
mode, as illustrated in the timing diagram in Figure 2. This
integration and A/D conversion process is controlled by
the system clock, CLK. The results from side A and side
B of each signal input are stored in a serial output shift
register. The DVALID output goes low when the shift
register contains valid data.
DVDD
CLK
CONV
IN1
RANGE0
Dual
Switched
Integrator
∆Σ
M odulato r
Digital
Filter
RANGE1
C ontro l
RANGE2
TEST
CLK_4X
IN3
HISPD/LOPWR
Dual
Switched
Integrator
RESET
IN2
Dual
Switched
Integrator
∆Σ
M odulato r
Digital
Filter
FORMAT
IN4
DCLK
Dual
Switched
Integrator
DCLK
IN5
DVALID
Dig ital
Dual
Switched
Integrator
∆Σ
Digital
M odulato r
Filter
In pu t/Output
DOUT
IN7
DOUT
Dual
Switched
Integrator
DIN
IN6
Dual
Switched
Integrator
∆Σ
Digital
M odulato r
Filter
IN8
Dual
Switched
Integrator
AGND
DGND
Figure 1. DDC118 Block Diagram
8
DIN
""#
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SBAS325B − JUNE 2004 − REVISED APRIL 2009
The digital interface of the DDC118 provides the digital
results via a synchronous serial interface consisting of
differential data clocks (DCLK and DCLK), a valid data pin
(DVALID), differential serial data output pins (DOUT and
DOUT), and differential serial data input pins (DIN and
DIN). The DDC118 contains only four A/D converters, so
the conversion process is interleaved (see Figure 2). The
integration and conversion process is fundamentally
independent of the data retrieval process. Consequently,
the CLK frequency and DCLK frequencies need not be the
same. DIN and DIN are only used when multiple
converters are cascaded, and otherwise should both be
tied to DGND.
implement the integration cycle. The timing relationships
of all of the switches shown in Figure 3 are illustrated in
Figure 4. Figure 4 is used to conceptualize the operation
of the integrator input stage of the DDC118 and should not
be used as an exact timing tool for design. See Figure 5 for
the block diagrams of the reset, integrate, wait and convert
states of the integrator section of the DDC118. This
internal switching network is controlled externally with the
convert
pin
(CONV),
range
selection
pins
(RANGE0-RANGE2), and the system clock (CLK). For the
best noise performance, CONV must be synchronized
with the rising edge of CLK. It is recommended that CONV
toggle within ±10ns of the rising edge of CLK.
DEVICE OPERATION
The noninverting inputs of the integrators are connected to
ground. Consequently, the DDC118 analog ground should
be as clean as possible. The range switches, along with
the internal and external capacitors (CF), are shown in
parallel between the inverting input and output of the
operational amplifier. At the beginning of a conversion, the
switches SA/D, SINTA, SINTB, SREF1, SREF2, and SRESET
are set (see Figure 4).
Basic Integration Cycle
The topology of the front end of the DDC118 is an analog
integrator as shown in Figure 3. In this diagram, only Input
IN1 is shown. This representation of the input stage
consists of an operational amplifier, a selectable feedback
capacitor network (CF), and several switches that
IN1, IN2, IN5, and IN6,
Integrator A
Integrate
Integrate
IN1, IN2, IN5, and IN6,
Integrator B
Integrate
Integrate
IN3, IN4, IN7, and IN8,
Integrator A
Integrate
Integrate
IN3, IN4, IN7, and IN8,
Integrator B
Integrate
Conversion in Progress
IN1B
IN2B
IN5B
IN6B
IN3B
IN4B
IN7B
IN8B
IN1A
IN2A
IN5A
IN6A
IN3A
IN4A
IN7A
IN8A
Integrate
IN1B
IN2B
IN5B
IN6B
IN3B
IN4B
IN7B
IN8B
IN1A
IN2A
IN5A
IN6A
IN3A
IN4A
IN7A
IN8A
DVALID
Figure 2. Basic Integration and Conversion Timing for the DDC118 (continuous mode)
SREF1
VREF
3pF
50pF
RANGE2
25pF
RANGE1
12.5pF
Input
Current
Photodiode
RANGE0
SINTA
SREF2
IN1
ESD
Protection
Diodes
SA/D1A
SRESET
SINTB
To Converter
Integrator A
Integrator B (same as A)
Figure 3. Basic Integration Configuration for Input 1, shown with a 250pC (CF = 62.5pF) Input Range
9
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SBAS325B − JUNE 2004 − REVISED APRIL 2009
CONV
CLK
SINTA
SINTB
SREF1
SREF2
SRESET
Integrate
Convert
Wait
W a it
Wait
R e se t
Convert
W a it
Configuration of
Integrator A
R e se t
SA/D1A
VREF
Integrator A
Voltage Output
Figure 4. Basic Integration Timing Diagram (as shown in Figure 3)
SREF1
CF
VREF
SINT
SREF2
CF
IN
SREF1
VREF
To Converter
SRESET
SA/D
SINT
SREF2
IN
To Converter
SRESET
SA/D
a) Reset Configuration
CF
SREF1
b) Wait Configuration
VREF
SINT
SREF2
CF
IN
SRESET
SREF1
VREF
To Converter
SA/D
SINT
SREF2
IN
SRESET
c) Integrate Configuration
To Converter
SA/D
d) Convert Configuration
Figure 5. Diagrams for the Four Configurations of the Front End Integrators of the DDC118
10
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Voltage Reference
At the completion of an A/D conversion, the charge on the
integration capacitor (CF) is reset with SREF1 and SRESET
(see Figure 4 and Figure 5a). In this manner, the selected
capacitor is charged to the reference voltage, VREF. Once
the integration capacitor is charged, SREF1 and SRESET
are switched so that VREF is no longer connected to the
amplifier circuit while it waits to begin integrating (see
Figure 5b). With the rising edge of CONV, SINTA closes,
which begins the integration of side A. This process puts
the integrator stage into its integrate mode (see Figure 5c).
The external voltage reference is used to reset the
integration capacitors before an integration cycle begins.
It is also used by the ∆Σ converter while the converter is
measuring the voltage stored on the integrators after an
integration cycle ends. During this sampling, the external
reference must supply the charge needed by the ∆Σ
converter. For an integration time of 400µs, this charge
translates to an average VREF current of approximately
150µA. The amount of charge needed by the ∆Σ converter
is independent of the integration time; therefore,
increasing the integration time lowers the average current.
For example, an integration time of 800µs lowers the
average VREF current to 75µA.
Charge from the input signal is collected on the integration
capacitor, causing the voltage output of the amplifier to
decrease. The falling edge of CONV stops the integration
by switching the input signal from side A to side B (SINTA
and SINTB). Prior to the falling edge of CONV, the signal on
side B was converted by the A/D converter and reset
during the time that side A was integrating. With the falling
edge of CONV, side B starts integrating the input signal.
Now the output voltage of the side A operational amplifier
is presented to the input of the ∆Σ A/D converter (see
Figure 5d).
It is critical that VREF be stable during the different modes
of operation (see Figure 5). The ∆Σ converter measures
the voltage on the integrator with respect to VREF. Since
the integrator capacitors are initially reset to VREF, any
drop in VREF from the time the capacitors are reset to the
time when the converter measures the integrator output
will introduce an offset. It is also important that VREF be
stable over longer periods of time because changes in
VREF correspond directly to changes in the full-scale
range. Finally, VREF should introduce as little additional
noise as possible.
Integration Capacitors
There are eight different capacitors available on-chip for
both sides of every channel in the DDC118. These internal
capacitors are trimmed in production to achieve the
specified performance for range error of the DDC118. The
range control pins (RANGE0-RANGE2) change the
capacitor value for all four integrators. Consequently, all
inputs and both sides of each input will always have the
same full-scale range. Table 1 shows the capacitor value
selected for each range selection.
For these reasons, it is strongly recommended that the
external reference source be buffered with an operational
amplifier, as shown in Figure 6. In this circuit, the voltage
reference is generated by a 4.096V reference. A low-pass
filter to reduce noise connects the reference to an
operational amplifier configured as a buffer. This amplifier
should have low noise, and input/output common-mode
ranges that support VREF. Following the buffer are
capacitors placed close to the DDC118 VREF pin. Even
though the circuit in Figure 6 might appear to be unstable
because of the large output capacitors, it works well for
most operational amplifiers. It is NOT recommended that
series resistance be placed in the output lead to improve
stability since this can cause a drop in VREF, which
producing large offsets.
Table 1. Range Selection of the DDC118
RANGE2
RANGE1
RANGE0
CF
(pF, typ)
INPUT RANGE
(pC, typ)
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
3
12.5
25
37.5
50
62.5
75
87.5
−0.048 to 12
–0.2 to 50
–0.4 to 100
–0.6 to 150
–0.8 to 200
–0.1 to 250
–1.2 to 300
–1.4 to 350
+5V
+5V
0.10µF
0.47µF
7
2
1
REF3140
10kΩ
3
OPA350
+
+
10µF
3
To VREF
Pin 10 of
the DDC118
6
2
0.10µF
10µF
0.1µF
4
Figure 6. Recommended External Voltage Reference Circuit for Best Low-Noise Operation with the DDC118
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DDC118 Frequency Response
Test Mode
The frequency response of the DDC118 is set by the front
end integrators and is that of a traditional continuous time
integrator, as shown in Figure 7. By adjusting TINT, the
user can change the 3dB bandwidth and the location of the
notches in the response. The frequency response of the
∆Σ converter that follows the front end integrator is of no
consequence because the converter samples a held
signal from the integrators. That is, the input to the ∆Σ
converter is always a DC signal. Since the output of the
front end integrators are sampled, aliasing can occur.
Whenever the frequency of the input signal exceeds
one-half of the sampling rate, the signal will fold back down
to lower frequencies.
When Test Mode is used, the inputs (IN1, IN2, IN3, IN4,
IN5, IN6, IN7, and IN8) are disconnected from the DDC118
integrators to enable the user to measure a zero input
signal regardless of the current supplied to the inputs. In
addition, packets of charge can be transferred to the
integrators in 11pC intervals to measure non-zero values.
The test mode works with both the continuous and
non-continuous modes. The timing diagram for the test
mode is shown in Figure 8 with the timing specifications
given in Table 2.
To enter Test Mode, hold TEST high while CONV
transitions. If TEST is held high during the entire
integration period, the integrators measure a zero value.
This mode can be used to help debug a design or perform
diagnostic tests. To apply packets of charge during Test
Mode, simply strobe TEST low then high before the next
CONV transition. Each rising edge of TEST causes
approximately 11pC of charge to be transferred to the
integrators. This charge transfer is independent of the
integration time. Data retrieval during Test Mode is
identical to normal operation. To exit Test Mode, take
TEST low and allow several cycles after exiting before
using the data.
0
G ain (dB)
−10
−20
−30
−40
−50
1
TINT
0.1
TINT
10
TINT
100
TINT
Frequency
Figure 7. Frequency Response of the DDC118
Test Mode Enabled: Inputs Disconnected
Test Mode Disabled
Test Mode Disabled
Action
Integrate B
Integrate A
0pC into B
11pC into A
22pC into B
33pC into A
Integrate B
Integrate A
CONV
t4
t6
t2
TEST
t1
t3
t5
t4
Figure 8. Timing Diagram of the Test Mode of the DDC118
Table 2. Timing for the DDC118 in the Test Mode
12
SYMBOL
DESCRIPTION
MIN
t1
Setup Time for Test Mode Enable
100
TYP
MAX
UNITS
ns
t2
Setup Time for Test Mode Disable
100
ns
t3
Hold Time for Test Mode Enable
100
ns
t4
From Rising Edge of TEST to the Edge of CONV while Test Mode
Enabled
1
µs
t5
Falling Edge to Rising Edge of TEST
1
µs
t6
Rising Edge to Falling Edge of TEST
1
µs
""#
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SBAS325B − JUNE 2004 − REVISED APRIL 2009
DIGITAL INTERFACE
The digital interface of the DDC118 provides the digital
results via a synchronous serial interface consisting of
differential data clocks (DCLK and DCLK), a valid data pin
(DVALID), differential serial data output pins (DOUT and
DOUT), and differential serial data input pins (DIN and
DIN). The DDC118 contains only four A/D converters, so
the conversion process is interleaved (see Figure 2,
page 9). The integration and conversion processes are
independent of the data retrieval process. Consequently,
the CLK frequency and DCLK frequencies need not be the
same. DIN and DIN are used when multiple converters are
cascaded. Cascading or daisy-chaining greatly simplifies
the interconnection and routing of the digital outputs in
cases where a large number of converters are needed.
Refer to the Cascading Multiple Converters section of this
data sheet for more detail.
High-Speed and Low-Power Modes
(HISPD/LOPWR)
The HISPD/LOPWR input controls the power dissipation
and in turn, the maximum allowable CLK frequency and
data rate, as shown in Table 4. With HISPD/LOPWR = 0,
the Low-Power Mode is selected with a typical 13.5mW/
channel and a maximum data rate of 2.5kSPS. Setting
HISPD/LOPWR = 1 selects the High-Speed Mode, which
supports a maximum data rate of 3.125kSPS with a corresponding typical power of 18.0mW/channel.
Table 4. HISPD/LOPWR Pin Operation
HISPD/
LOPWR
MODE
TYPICAL
POWER/
CHANNEL
MAXIMUM
CLK FREQUENCY
(CLK_4X = 0)
MAXIMUM
DATA
RATE
0
Low-Power
13.5mW/ch
4.0MHz
2.5kSPS
1
High-Speed
18.0mW/ch
4.8MHz
3.125kSPS
Data Valid (DVALID)
Complementary Signals (DCLK, DIN, and DOUT)
The DDC118 provides optional complementary inputs
(DCLK, DIN) to help reduce digital coupling to the analog
inputs. If using these inputs, connect a complementary
signal to each. If these inputs are not connected on the
DDC118, they should be tied to DGND. DOUT is a
complementary output designed to drive DIN. If not using
DOUT, leave it floating.
System and Data Clocks (CLK and CONV)
The system clock is supplied to CLK and the data clock is
supplied to DCLK. Make sure the clock signals are
clean—avoid overshoot or ringing. For best performance,
generate both clocks from the same clock source. DCLK
should be disabled by taking it low after the data has been
shifted out or while CONV is transitioning.
When using multiple DDC118s, pay close attention to the
DCLK distribution on the printed circuit board (PCB). In
particular, make sure to minimize skew in the DCLK signal
as this can lead to timing violations in the serial interface
specifications. See the Cascading Multiple Converters
section for more details.
System Clock Divider (CLK_4X)
The DVALID signal indicates that data is ready. Data
retrieval may begin after DVALID goes low. This signal is
generated using an internal clock divided down from the
system clock CLK. The phase relationship between this
internal clock and CLK is set when power is first applied
and is random. Since the user must synchronize CONV
with CLK, the DVALID signal will have a random phase
relationship with CONV. This uncertainty is ± 1/fCLK.
Polling DVALID eliminates any concern about this
relationship. If data read back is timed from CONV, wait the
maximum value of t7 or t8 to insure data is valid.
Reset (RESET)
The DDC118 is reset asynchronously by taking the
RESET input low, as shown in Figure 9. Make sure the
reset pulse is at least 50µs wide. After resetting the
DDC118, wait at least four conversions before using the
data. It is very important to make sure the RESET is glitch
free to avoid unintended resets. The RESET pin is used
during power-up; see the Power-Up Sequence section for
more details.
> 50µs
RESET
The CLK_4X input enables an internal divider on the
system clock as shown in Table 3. When CLK_4X = 1, the
system clock is divided by four. This allows a 4X faster
system clock, which in turn provides a finer quantization of
the integration time as the CONV signal needs to be
synchronized with the system clock for the best
performance.
Table 3. CLK_4X Pin Operation
CLK_4X
PIN
CLK DIVIDER
VALUE
TYPICAL CLK
FREQUENCY
INTERNAL CLOCK
FREQUENCY
0
1
4MHz
4MHz
1
4
16MHz
4MHz
Figure 9. Reset Timing
Convert (CONV)
CONV controls the integration time (TINT). For optimum
analog performance, make sure CONV is synchronized to
CLK.
This recommendation implies that while SPEED is low,
TINT needs to be adjusted in steps of 250ns if CLK_4X is
low and CLK = 4MHz. If CLK_4X is high and CLK =
16MHz, this allows TINT to be adjusted in steps of 62.5ns.
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Conversion Rate
The conversion rate of the DDC118 is set by a combination
of the integration time (determined by the user) and the
speed of the A/D conversion process. The A/D conversion
time is primarily a function of the system clock (CLK)
speed. One A/D conversion cycle encompasses the
conversion of two signals (one side of each dual integrator
feeding the modulator) and the reset time for each of the
integrators involved in the two conversions. In most
situations, the A/D conversion time is shorter than the
integration time. If this condition exists, the DDC118 will
operate in the continuous mode. When the DDC118 is in
the continuous mode, the sensor output is continuously
integrated by one of the two sides of each input.
In the event that the A/D conversion takes longer than the
integration time, the DDC118 will switch into a
non-continuous mode. In non-continuous mode, the A/D
converter is not able to keep pace with the speed of the
integration process. Consequently, the integration
process is periodically halted until the digitizing process
catches up. These two basic modes of operation for the
DDC118—continuous and non-continuous modes—are
described below.
CONV|mbsy
1
2
CONV × mbsy
Ncont
Ncont
CONV
3
Int A
Cont
CONV × mbsy
CONV
4
5
CONV × mbsy
Int B/Meas A
Cont
CONV × mbsy
Int A/Meas B
Cont
CONV
6
CONV × mbsy
Int B
Cont
CONV
7
Ncont
8
CONV × mbsy
Ncont
CONV|mbsy
Continuous and Non-Continuous Operational
Modes
Figure 10 shows the state diagram of the DDC118. In all,
there are eight states. Table 5 provides a brief explanation
of each state.
Table 5. State Descriptions
STATE
MODE
DESCRIPTION
1
Ncont
Complete m/r/az of side A, then side B (if previous
state is state 4). Initial power-up state when CONV
is initially held HIGH.
2
Ncont
Prepare side A for integration.
3
Cont
Integrate on side A.
4
Cont
Integrate on side B; m/r/az on side A.
5
Cont
Integrate on side A; m/r/az on side B.
6
Cont
Integrate on side B.
7
Ncont
Prepare side B for integration.
8
Ncont
Complete m/r/az of side B, then side A (if previous
state is state 5). Initial power-up state when CONV
is initially held LOW.
Four signals are used to control progression around the
state diagram: CONV, mbsy, and their complements. The
state machine uses the level as opposed to the edges of
CONV to control the progression. mbsy is an internallygenerated signal not available to the user. It is active
whenever a measurement/reset/auto-zero (m/r/az) cycle
is in progress.
14
Figure 10. Integrate/Measure State Diagram
During the cont mode, mbsy is not active when CONV
toggles. The non-integrating side is always ready to begin
integrating when the other side finishes its integration.
Consequently, monitoring the current status of CONV is all
that is needed to know the current state. Cont mode
operation corresponds to states 3-6. Two of the states, 3
and 6, only perform an integration (no m/r/az cycle).
mbsy becomes important when operating in the ncont
mode, states 1, 2, 7, and 8. Whenever CONV is toggled
while mbsy is active, the DDC118 will enter or remain in
either ncont state 1 (or 8). After mbsy goes inactive, state
2 (or 7) is entered. This state prepares the appropriate side
for integration. In the ncont states, the inputs to the
DDC118 are grounded.
One interesting observation from the state diagram is that
the integrations always alternate between sides A and B.
This relationship holds for any CONV pattern and is
independent of the mode. States 2 and 7 insure this
relationship during the ncont mode.
When power is first applied to the DDC118, the beginning
state is either 1 or 8, depending on the initial level of CONV.
For CONV held high at power-up, the beginning state is 1.
Conversely, for CONV held low at power-up, the beginning
state is 8. In general, there is a symmetry in the state
diagram between states 1-8, 2-7, 3-6, and 4-5. Inverting
CONV results in the states progressing through their
symmetrical match.
""#
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TIMING EXAMPLES
measurement cycles are underway. The internal signal
mbsy is shown next. Finally, DVALID is given. DVALID
goes active low when data is ready to be retrieved from the
DDC118. It stays low until DCLK is taken high and then
back low by the user. The text below the DVALID pulse
indicates the side of the data available to be read, and
arrows help match the data to the corresponding
integration. The signals illustrated in Figure 11 through
Figure 19 are drawn at approximately the same scale.
Cont Mode
A few timing diagrams help illustrate the operation of the
state machine. These diagrams are shown in Figure 11
through Figure 19. Table 6 gives generalized timing
specifications in units of CLK periods for CLK_4X = 0. If
CLK_4X = 1, these values increase by a factor of four
because of the internal clock divider. Values (in µs) for
Table 6 can be easily found for a given CLK. For example,
if CLK = 4MHz, then a CLK period = 0.25µs. t6 in Table 6
would then be 367.50 ± 0.125µs.
In Figure 11, the first state is ncont state 8. The DDC118
always powers up in the ncont mode. In this case, the first
state is 8 because CONV is initially low. After the first two
states, cont mode operation is reached and the states
begin toggling between 4 and 5. From now on, the input is
being continuously integrated, either on side A or side B.
The time needed for the m/r/az cycle, or t6, is the same time
that determines the boundary between the cont and ncont
modes described earlier in the Overview section. DVALID
goes low after CONV toggles in time t7, indicating that data
is ready to be retrieved. As shown in Figure 11, there are
two values for t6 and t7. The reason for this is discussed in
the Special Considerations section.
Table 6. Timing Specifications Generalized in
CLK Periods
DESCRIPTION
VALUE
(CLK periods with CLK_4X = 0)
t6
t7
Cont mode m/r/az cycle
1470 ± 0.5
Cont mode data ready
1380 ± 0.5
t8
t9
1st ncont mode data ready
1379 ± 1
2nd ncont mode data ready
1450
t10
Ncont mode m/r/az cycle
2901 ± 1
SYMBOL
Figure 11 shows a few integration cycles beginning with
initial power-up for a cont mode example. The top signal
is CONV and is supplied by the user. The next line
indicates the current state in the state diagram. The
following two traces show when integrations and
See Figure 12 for the timing diagram of the internal
operations occurring during continuous mode operation.
Table 7 gives the timing specifications in the continuous
mode.
CONV
State
8
Integration
Status
7
6
5
4
5
Integrate B
Integrate A
Integrate B
Integrate A
m/r/az
Status
m/r/az B
m/r/az A
m/r/az B
t6
mbsy
DVALID
t7
t=0
Power−Up
Side B
Data
Side A
Data
Side B
Data
SYMBOL
DESCRIPTION
VALUE (CLK = 4MHz, CLK_4X = 0)
VALUE (CLK = 4.8MHz, CLK_4X = 0)
t6
Cont Mode m/r/az Cycle
367.50 ± 0.125µs
306.25 ± 0.104µs
t7
Cont Mode Data Ready
345.00 ± 0.125µs
287.5 ± 0.104µs
Figure 11. Continuous Mode Timing
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End Integration Side B
Start Integration Side A
End Integration Side A
Start Integration Side B
TINT
CONV
TINT
Side A
A/D Conversion
Inputs 1, 2, 5, and 6 (Internal)
End Integration Side A
Start Integration Side B
Side A
t14
Side B
t12
Side A
A/D Conversion
Inputs 3, 4, 7, and 8 (Internal)
Side B
t 13
t12
t 13
t 14
DVALID
Side A
Data Ready
Side B
Data Ready
Figure 12. Timing Diagram of the Internal Operation in Continuous Mode of the DDC118
Table 7. Timing for the Internal Operation in Continuous Mode
CLK = 4MHz, CLK_4X = 0
SYMBOL
TINT
t12
t13
t14
16
DESCRIPTION
MIN
Integration Period (continuous mode)
400
TYP
CLK = 4.8MHz, CLK_4X = 0
MAX
MIN
1,000,000
320
TYP
MAX
UNITS
1,000,000
µs
169.5
141.25
µs
A/D Conversion Reset Time (internally controlled)
4
3.333
µs
Integrator and A/D Conversion Reset Time
(internally controlled)
23
19.167
µs
A/D Conversion Time (internally controlled)
""#
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Ncont Mode
Non-continuous mode of operation is intended for Ranges
1 to 7. It is not recommended to use Range 0 when
operating in non-continuous mode. Figure 13 illustrates
operation in the ncont mode. The integrations come in
pairs (that is, sides A/B or sides B/A) followed by a time
during which no integrations occur. During that time, the
previous integrations are being measured, reset and
auto-zeroed. Before the DDC118 can advance to states 3
or 6, both sides A and B must be finished with the m/r/az
cycle which takes time t10. When the m/r/az cycles are
completed, time t11 is needed to prepare the next side for
integration. This time is required for the ncont mode
because the m/r/az cycle of the ncont mode is slightly
different from that of the cont mode. After the first
integration ends, DVALID goes low in time t8. This time is
the same as in the cont mode. The second data will be
ready in time t9 after the first data is ready. One result of the
naming convention used in this data sheet is that when the
DDC118 is operating in the ncont mode, it passes through
both ncont mode states and cont mode states. For
example, in Figure 13, the state pattern is 3, 4, 1, 2, 3, 4,
1, 2, 3, 4 ... where 3 and 4 are cont mode states. Ncont
mode, by definition, means that for some portion of the
time, neither side A nor B is integrating. States that perform
an integration are labeled cont mode states, while those
that do not are called ncont mode states. Since
integrations are performed in the ncont mode, just not
continuously, some cont mode states must be used in a
ncont mode state pattern.
CONV
State
3
4
1
2
3
4
1
2
t 11
Integration
Status
m/r/az
Status
Int A
Int B
Int A
m/r/az A
Int B
m/r/az A
m/r/az B
m/r/az B
t 10
mbsy
t9
DVALID
t8
Side A
Data
Side B
Data
Side A
Data
Side B
Data
SYMBOL
DESCRIPTION
VALUE (CLK = 4MHz, CLK_4X = 0)
VALUE (CLK = 4.8MHz, CLK_4X = 0)
t8
t9
t10
t11
1st ncont Mode Data Ready
2nd ncont Mode Data Ready
ncont Mode m/r/az Cycle
Prepare Side for Integration
344.75 ± 0.25µs
362.5µs
725.25 ± 0.25µs
≥ 18µs
287.292 ± 0.208µs
302.083µs
604.375 ± 0.208µs
≥ 15µs
Figure 13. Non-Continuous Mode Timing
17
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Start Integration Side A
Start Integration Side A
End Integration Side A
Start Integration Side B
End Integration Side B
Release
State
Wait State
TINT
t17
CONV
TINT
t 16
A/D Conversion
Inputs 1, 2, 5, and 6
t12
A/D Conversion
Inputs 3, 4, 7, and 8
t12
t13
t 15
DVALID
Side A
Data Ready
Side B
Data Ready
Figure 14. Conversion Detail for the Internal Operation of Non-Continuous Mode with Side A Integrated
First
Table 8. Internal Timing for the DDC118 in Non-Continuous Mode
CLK = 4MHz, CLK_4X = 0
SYMBOL
TINT
DESCRIPTION
MIN
Integration Time (non-continuous mode)
TYP
400
t12
A/D Conversion Time (internally controlled)
t13
A/D Conversion Reset Time (internally controlled)
t15
Integrator and A/D Conversion Reset Time
(internally controlled)
t16
Total A/D Conversion and Reset Time (internally controlled)
t17
Release Time
CLK = 4.8MHz, CLK_4X = 0
MAX
MIN
1,000,000
320
MAX
1,000,000
UNITS
µs
169.5
141.25
µs
4
3.333
µs
19.5
16.25
µs
604.375 ± 0.208
µs
725.25 ± 0.25
18
TYP
µs
15
Start Integration Side A
Start Integration Side A
End Integration Side A
Start Integration Side B
End Integration Side B
Release
State
Wait State
TINT
t17
CONV
TINT
t 16
A/D Conversion
Inputs 1, 2, 5, and 6
t12
A/D Conversion
Inputs 3, 4, 7, and 8
t12
t13
t 15
DVALID
Side A
Data Ready
Side B
Data Ready
Figure 15. Internal Operation Timing Diagram of Non-Continuous Mode with Side B Integrated First
18
""#
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SBAS325B − JUNE 2004 − REVISED APRIL 2009
cycle CONV signal with TINT = 512 CLK periods. Care
must be exercised when using a square wave to generate
CONV. There are certain integration times that must be
avoided since they produce very short intervals for state 2
(or state 7 if CONV is inverted). As seen in the state
diagram, the state progresses from 2 to 3 as soon as
CONV is high. The state machine does not insure that the
duration of state 2 is long enough to properly prepare the
next side for integration (t11). This must be done by the
user with proper timing of CONV. For example, if CONV is
a square wave with TINT = 970 CLK periods, state 2 will
only be 9 CLK periods long; therefore, t11 will not be met.
Looking at the state diagram, one can see that the CONV
pattern needed to generate a given state progression is not
unique. Upon entering states 1 or 8, the DDC118 remains
in those states until mbsy goes low, independent of CONV.
As long as the m/r/az cycle is underway, the state machine
ignores CONV (see Figure 10, page 14). The top two
signals in Figure 16 are different CONV patterns that
produce the same state. This feature allows flexibility in
generating ncont mode CONV patterns. For example, the
DDC118 Evaluation Fixture operates in the ncont mode by
generating a square wave with pulse width < t6. Figure 17
illustrates operation in the ncont mode using a 50% duty
CONV1
CONV2
mbsy
State
3
4
1
2
3
4
1
2
Figure 16. Equivalent CONV Signals in Non-Continuous Mode
CONV
State
Integration
Status
3
4
Int A
Int B
1
2
3
4
Int A
Int B
1
mbsy
DVALID
Side A
Data
Side B
Data
Side A
Data
Figure 17. Non-Continuous Mode Timing with a 50% Duty Cycle CONV Signal
19
""#
www.ti.com
SBAS325B − JUNE 2004 − REVISED APRIL 2009
Changing Between Modes
Changing from the ncont to cont mode occurs when TINT
is increased so that TINT is always ≥ t6, as shown in
Figure 19 (see also Figure 14 and Table 8, page 18). With
a longer TINT, the m/r/az cycle has enough time to finish
before the next integration begins and continuous
integration of the input signal is possible. For the special
case of the very first integration when changing to the cont
mode, TINT can be < t6. This is allowed because there is
no simultaneous m/r/az cycle on the side B during state
3—there is no need to wait for it to finish before ending the
integration on side A.
Changing from the cont to ncont mode occurs whenever
TINT < t6. Figure 18 shows an example of this transition.
In this figure, the cont mode is entered when the integration
on side A is completed before the m/r/az cycle on side B
is complete. The DDC118 completes the measurement on
sides B and A during states 8 and 7 with the input signal
shorted to ground. Ncont integration begins with state 6.
CONV
State
5
4
5
8
Continuous
Integration
Status
m/r/az
Status
Integrate A
Integrate B
m/r/az B
m/r/az A
7
6
5
Int B
Int A
Non−Continuous
Int A
m/r/az B
m/r/az A
m/r/az B
mbsy
Figure 18. Changing from Continuous Mode to Non-Continuous Mode
CONV
State
3
4
1
2
Non−Continuous
Integration
Status
m/r/az
Status
Int A
Int B
m/r/az A
3
Continuous
Integrate A
m/r/az B
4
Integrate B
m/r/az A
mbsy
Figure 19. Changing from Non-Continuous Mode to Continuous Mode
20
""#
www.ti.com
SBAS325B − JUNE 2004 − REVISED APRIL 2009
DATA FORMAT (FORMAT)
DATA RETRIEVAL
The serial output data is provided in an offset binary code
as shown in Table 9. The digital input pin FORMAT selects
how many bits are used in the output word. When
FORMAT is high (1), 20 bits are used. When FORMAT is
low (0), the lower 4 bits are truncated so that only 16 bits
are used. Note that the LSB size is 16 times bigger when
FORMAT = 0. An offset is included in the output to allow
slightly negative inputs, from board leakages for example,
from clipping the reading. This offset is approximately
0.4% of the positive full-scale.
Table 9. Ideal Output Code(1) vs Input Signal
INPUT
SIGNAL
IDEAL OUTPUT CODE
FORMAT = HIGH (1)
IDEAL OUTPUT CODE
FORMAT = LOW (0)
≥ 100% FS
1111 1111 1111 1111 1111
1111 1111 1111 1111
0.001531% FS
0000 0001 0000 0001 0000
0000 0001 0000 0001
0.001436% FS
0000 0001 0000 0000 1111
0000 0001 0000 0000
0.000191% FS
0000 0001 0000 0000 0010
0000 0001 0000 0000
0.000096% FS
0000 0001 0000 0000 0001
0000 0001 0000 0000
0% FS
0000 0001 0000 0000 0000
0000 0001 0000 0000
−0.3955% FS
0000 0000 0000 0000 0000
0000 0000 0000 0000
In both the continuous and non-continuous modes of
operation, the data from the last conversion is available for
retrieval on the falling edge of DVALID (see Figure 20 and
Table 10). Data is shifted out on the falling edge of the data
clock, DCLK. Make sure not to retrieve data while CONV
changes as this can introduce noise. Stop activity on
DCLK at least 10µs before or after a CONV transition.
Setting the FORMAT pin = 0 (16-bit output word) reduces
the time needed to retrieve data by 20%, since there are
fewer bits to shift out. This time reduction can be useful in
multichannel systems requiring only 16 bits of resolution.
(1) Excludes the effects of noise, INL, offset, and gain errors.
CLK
t18
DVALID
t20
t20
t19
DCLK
t21
DOUT
Input 8
MSB
Input 8
LSB
Input 7
MSB
Input 5
LSB
Input 4
MSB
Input 2
LSB
Input 1
MSB
Input 1
LSB
Input 8
MSB
Figure 20. Digital Interface Timing Diagram for Data Retrieval From a Single DDC118
Table 10. Timing for the DDC118 Data Retrieval
CLK = 4MHz, CLK_4X = 0
SYMBOL
t18
t19
t20
t21
t21A(1)
DESCRIPTION
MIN
TYP
MAX
CLK = 4.8MHz, CLK_4X = 0
MIN
Propagation Delay from Falling Edge of CLK to DVALID LOW
5
5
Propagation Delay from Falling Edge of DCLK to DVALID HIGH
5
5
Hold Time that DOUT is Valid Before the Falling Edge of DVALID
Hold Time that DOUT is Valid After Falling Edge of DCLK
Propagation Delay from Falling Edge of DCLK to Valid DOUT
1.75
TYP
MAX
ns
ns
µs
1.458
5
5
10
UNITS
ns
10
ns
(1) With a maximum load of one DDC118 (4pF typical) with an additional load of (5pF).
21
""#
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SBAS325B − JUNE 2004 − REVISED APRIL 2009
DDC118 devices together to minimize wiring. In this mode
of operation, the serial data output is shifted through
multiple DDC118s, as illustrated in Figure 21.
SPECIAL CONSIDERATIONS
Cascading Multiple Converters
Multiple DDC118 units can be connected in serial
configuration, as illustrated in Figure 21.
See Figure 22 for the timing diagram when the DIN input
is used to daisy-chain several devices. Table 11 gives the
timing specification for data retrieval using DIN.
DOUT can be used with DIN to daisy-chain several
Sensor A B C D E F G H
I
DIN
DOUT
DIN
DOUT
DCLK
DCLK
DVALID
DCLK
DDC118
DDC118
DIN
DIN
IN8
IN7
IN6
IN5
IN4
IN3
IN2
IN1
DOUT
IN6
IN5
IN4
IN3
IN2
IN1
DOUT
DIN
IN8
IN7
IN6
IN5
IN4
IN3
IN2
IN1
DIN
DCLK
DVALID
DCLK
DDC118
DOUT
IN8
IN7
DOUT
Data Retrieval
Outputs
DCLK
DVALID
Data Clock
J K L M N O P
Q R S T U V W X
Figure 21. Daisy-Chained DDC118s
CLK
t18
DVALID
t20
t 20
t19
DCLK
t21
t 23
t22
DIN
Input A
MSB
DOUT
Input A
LSB
Input B
MSB
Input L
LSB
Input M
MSB
Input W
LSB
Input X
MSB
Input X
LSB
Input A
MSB
Figure 22. Timing Diagram When Using the DIN Function of the DDC118
Table 11. Timing for the DDC118 Data Retrieval Using DIN
22
SYMBOL
DESCRIPTION
MIN
TYP
MAX
UNITS
t22
Set-Up Time From DIN to Falling Edge of DCLK
5
ns
t23
Hold Time For DIN After Falling Edge of DCLK
4
ns
""#
www.ti.com
SBAS325B − JUNE 2004 − REVISED APRIL 2009
RETRIEVAL BEFORE CONV TOGGLES
(CONTINUOUS MODE)
NOTE: 128τDCLK is used for FORMAT = low.
where τDCLK is the period of the data clock. For example,
if TINT = 1000µs and DCLK = 10MHz, the maximum
number of DDC118s (FORMAT = high) is shown in
Equation 2:
Date retrieval before CONV toggles is the most
straightforward method. Data retrieval begins soon after
DVALID goes low and finishes before CONV toggles, as
shown in Figure 23. For best performance, data retrieval
must stop t28 before CONV toggles. This method is most
appropriate for longer integration times. The maximum
time available for readback is TINT – t27 – t28. For DCLK =
10MHz and CLK = 4MHz, the maximum number of
DDC118s that can be daisy-chained together (FORMAT =
high) is calculated by Equation 1:
T INT * 355.125ms
160t DCLK
CONV
DVALID
1000ms * 355.125ms
+ 40.30 ³ 40DDC118s
(160)(100ns)
(1)
TINT
TINT
t27
t28
DCLK
…
…
DOUT
…
…
Side B
Data
Side A
Data
CLK = 4MHz, CLK_4X = 0
SYMBOL
(2)
(or 50 for FORMAT = low).
CLK = 4.8MHz, CLK_4X = 0
DESCRIPTION
UNITS
MIN
TYP
MAX
MIN
345.00 ± 0.125
t27
Cont Mode Data Ready
t28
Data Retrieval Shutdown Before Edge of CONV
10
TYP
287.5 ± 0.104
10
MAX
µs
µs
Figure 23. Readback Before CONV Toggles
23
""#
www.ti.com
SBAS325B − JUNE 2004 − REVISED APRIL 2009
RETRIEVAL AFTER CONV TOGGLES
(CONTINUOUS MODE)
of DDC118s that can be daisy-chained together (FORMAT
= high) is calculated by Equation 3:
For shorter integration times, more time is available if data
retrieval begins after CONV toggles and ends before the
new data is ready. Data retrieval must wait t29 after CONV
toggles before beginning. See Figure 24 for an example of
this. The maximum time available for retrieval is
t27 − t29 – t26 (344.875µs – 10µs – 1.75µs for
CLK = 4MHz), regardless of TINT. The maximum number
TINT
CONV
333.125ms
160t DCLK
(3)
NOTE: 128τDCLK is used for FORMAT = low.
For DCLK = 10MHz, the maximum number of DDC118s is
20 (or 26 for FORMAT = low).
TINT
TINT
DVALID
t27
t29
DCLK
…
DOUT
t26
…
…
…
…
…
Side A
Data
Side B
Data
Side A
Data
CLK = 4MHz, CLK_4X = 0
SYMBOL
DESCRIPTION
MIN
t26
t27
Hold Time that DOUT is Valid Before Falling Edge of DVALID
t29
Data Retrieval Start-Up After Edge of CONV
Cont Mode Data Ready
TYP
MAX
MIN
TYP
MAX
UNITS
1.75
1.458
µs
345.00 ± 0.125
287.5 ± 0.104
µs
10
Figure 24. Readback After CONV Toggles
24
CLK = 4.8MHz, CLK_4X = 0
10
µs
""#
www.ti.com
SBAS325B − JUNE 2004 − REVISED APRIL 2009
RETRIEVAL BEFORE AND AFTER CONV
TOGGLES (CONTINUOUS MODE)
RETRIEVAL: NONCONTINUOUS MODE
Retrieving in noncontinuous mode is slightly different,
compared to the continuous mode. As illustrated in
Figure 26, DVALID goes low in time t30 after the first
integration completes. If TINT is shorter than this time, all
of t31 is available to retrieve data before the other side data
is ready. For TINT > t30, the first integration data is ready
before the second integration completes. Data retrieval
must be delayed until the second integration completes,
leaving less time available for retrieval. The time available
is t31 – (TINT – t30). The second integration’s data must be
retrieved before the next round of integration begins. This
time is highly dependent on the pattern used to generate
CONV. As with the continuous mode, data retrieval must
halt before and after CONV toggles (t28, t29) and be
completed before new data is ready (t26).
For the absolute maximum time for data retrieval, data can
be retrieved before and after CONV toggles. Nearly all of
TINT is available for data retrieval. Figure 25 illustrates
how this is done by combining the two previous methods.
Retrieval during CONV toggling to prevent digital noise, as
discussed previously, and finished before the next data is
ready. The maximum number of DDC118s that can be
daisy-chained together (FORMAT = high) is:
T INT * 20ms * 1.75ms
160t DCLK
NOTE: 128τDCLK is used for FORMAT = low.
For TINT = 400µs and DCLK = 10MHz, the maximum
number of DDC118s is 23 (or 29 for FORMAT = low).
CONV
TINT
TINT
t29
DVALID
t26
t28
DCLK
DOUT
TINT
…
…
…
…
…
…
…
…
…
…
…
…
Side B
Data
SYMBOL
t26
t28
t29
Side A
Data
CLK = 4MHZ, CLK_4X = 0
DESCRIPTION
MIN
Hold Time that DOUT is Valid Before Falling Edge of DVALID
Data Retrieval Shutdown Before Edge of CONV
Data Retrieval Start-Up After Edge of CONV
TYP
CLK = 4.8MHZ, CLK_4X = 0
MAX
MIN
1.75
TYP
MAX
1.458
10
10
10
10
UNITS
µs
µs
µs
Figure 25. Readback Before and After CONV Toggles
T IN T
CONV
TIN T
T IN T
T IN T
DVALID
t3 0
SYMBOL
t30
t31
t3 1
DCLK
…
…
D OUT
…
…
Side A
Data
Side B
Data
DESCRIPTION
1st ncont Mode Data Ready
2nd ncont Mode Data Ready
CLK = 4MHz, CLK_4X = 0
MIN
TYP
MAX
CLK = 4.8MHz, CLK_4X = 0
MIN
TYP
MAX
UNITS
344.75 ± 0.25
362.500
287.292 ± 0.208
302.083
µs
µs
Figure 26. Readback in Non-Continuous Mode
25
""#
www.ti.com
SBAS325B − JUNE 2004 − REVISED APRIL 2009
POWER-UP SEQUENCING
Prior to power-up, all digital and analog inputs must be low.
After the power supplies have settled, release RESET
after time t32. (See Figure 28 and Table 12.) Wait for time
t33 to begin applying the digital signals CONV and CLK.
The first CONV pulse will complete the release state and
begin integration.
VA
AVDD
10µF
DDC118
VD
DVDD
LAYOUT
AGND
0.1µF
10µF
DGND
0.1µF
POWER SUPPLIES AND GROUNDING
Both AVDD and DVDD should be as quiet as possible. It
is particularly important to eliminate noise from AVDD that
is non-synchronous with the DDC118 operation. Figure 27
illustrates two acceptable ways to supply power to the
DDC118. The first case shows two separate +5V supplies
for AVDD and DVDD. In this case, each +5V supply of the
DDC118 should be bypassed with 10µF solid tantalum
capacitors and 0.1µF ceramic capacitors. The second
case shows the DVDD power supply derived from the
AVDD supply with a < 10Ω isolation resistor. In both cases,
the 0.1µF capacitors should be placed as close to the
DDC118 package as possible. It is recommended that
both the analog and digital grounds (AGND and DGND) be
connected to a single ground plane on the printed circuit
board (PCB).
Separate Supplies
+5V
AVDD
10µF
AGND
0.1µF
DDC118
< 10Ω
DVDD
DGND
0.1µF
One +5V Supply
Figure 27. Power-Supply Connection Options
THERMAL PAD
It is strongly recommended that the thermal pad on the
DDC118 be connected to ground on the PCB. No PCB
traces should be routed underneath the thermal pad.
AVDD
DVDD
t32
Release State
RESET
Start Integration
t 33
CONV
t34
CLK
…
Integrate Side B
Figure 28. Timing Diagram at Power-Up of the DDC118
Table 12. Timing for the DDC118 Power-Up Sequence
26
SYMBOL
DESCRIPTION
MIN
TYP
MAX
UNITS
t32
Power Supplies Settled to RESET Release
10
ms
t33
RESET Release to CONV, CLK Begin
50
µs
t34
First CONV Pulse Width
50
µs
""#
www.ti.com
SBAS325B − JUNE 2004 − REVISED APRIL 2009
Shielding Analog Signal Paths
currents between the PCB traces can exceed the input
bias current of the DDC118 if shielding is not implemented.
Figure 29 illustrates an acceptable approach to this
problem. A PC ground plane is placed around the inputs
of the DDC118. This shield helps minimize coupled noise
into the input pins.
As with any precision circuit, careful PCB layout ensures
the best performance. It is essential to make short, direct
interconnections
and
avoid
stray
wiring
capacitance—particularly at the analog input pins. Digital
signals should be kept as far from the analog input signals
as possible on the PCB.
This approach reduces leakage effects by surrounding
these sensitive pins with a low impedance analog ground.
Leakage currents from other portions of the circuit will flow
harmlessly to the low impedance analog ground rather
than into the analog input stage of the DDC118.
Input shielding practices should be taken into
consideration when designing the circuit layout for the
DDC118. The inputs to the DDC118 are high impedance
and extremely sensitive to extraneous noise. Leakage
Digital I/O and Digital Power
48
47
46
45
44
43
42
41
40
39
38
37
1
36
2
35
3
34
4
33
5
32
6
31
DDC118
7
30
8
29
9
28
10
27
11
26
12
25
13
14
15
16
17
Analog
Ground
18
19
20
21
22
23
Analog
Ground
IN8 IN4 IN7 IN3
Analog Power
24
Analog
Ground
IN6 IN2 IN5 IN1
Figure 29. Recommended Shield for DDC118 Layout Design
27
www.ti.com
SBAS325B − JUNE 2004 − REVISED APRIL 2009
Revision History
DATE
REV
4/09
B
PAGE
SECTION
1
Front Page
9
Theory of Operation
DESCRIPTION
Updated front page appearance.
Changed last sentence of first paragraph on page 9.
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
28
PACKAGE OPTION ADDENDUM
www.ti.com
9-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)
DDC118IRTCR
ACTIVE
VQFN
RTC
48
2500
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-3-260C-168 HR
-40 to 85
DDC118
DDC118IRTCT
ACTIVE
VQFN
RTC
48
250
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-3-260C-168 HR
-40 to 85
DDC118
DDC118IRTCTG4
ACTIVE
VQFN
RTC
48
250
Green (RoHS
& no Sb/Br)
CU NIPDAU
Level-3-260C-168 HR
-40 to 85
DDC118
(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
9-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
DDC118IRTCR
VQFN
RTC
48
2500
330.0
16.4
7.3
7.3
1.5
12.0
16.0
Q2
DDC118IRTCT
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)
DDC118IRTCR
VQFN
RTC
48
2500
350.0
350.0
43.0
DDC118IRTCT
VQFN
RTC
48
250
213.0
191.0
55.0
Pack Materials-Page 2
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IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT OF THIRD
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