ADS131B02-Q1
SBASAA3 – SEPTEMBER 2021
ADS131B02-Q1 Automotive, 2-Channel, 32-kSPS, Simultaneous-Sampling,
24-Bit, Delta-Sigma ADC
1 Features
3 Description
•
The ADS131B02-Q1 is a two-channel, simultaneoussampling, 24-bit, delta-sigma (ΔΣ) analog-to-digital
converter (ADC) that offers wide dynamic range, low
power, and buffered analog inputs, making the device
an excellent fit for automotive battery management
systems (BMS). The ADC inputs can be directly
interfaced to shunt resistors for bidirectional batterycurrent measurements, to resistor-divider networks
for high-voltage measurements, or to temperature
sensors (such as thermistors or analog output
temperature sensors).
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AEC-Q100 qualified for automotive applications:
– Temperature grade 1: –40°C to +125°C, TA
Functional Safety-Capable
– Documentation available to aid functional safety
system design
2 simultaneous-sampling, differential input ADCs
Programmable data rate: Up to 32 kSPS
Programmable gain: Up to 128
Noise performance:
– 0.82 μVRMS at 1 kSPS, gain = 8
Global-chop mode to remove offset drift over
temperature and time
High-impedance analog inputs for direct sensor
connection
Integrated negative charge pump allows input
signal measurements below ground
Crosstalk between channels: –120 dB
Low-drift internal reference: 1.2 V
Precision internal oscillator
CRC on communications and register map
Analog and digital supplies: 2.7 V to 3.6 V
Low power consumption: 3 mW at 3.3-V AVDD
and DVDD
2 Applications
•
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EV charging stations
– DC e-metering
Automotive battery management systems (BMS):
– Current-shunt measurements
– Voltage measurements using external resistor
dividers
– Temperature measurements using thermistors
or analog output temperature sensors
Energy storage systems (ESS)
The individual ADC channels can be independently
configured depending on the sensor input. A lownoise, programmable gain amplifier (PGA) provides
gains ranging from 1 to 128 to amplify low-level
signals. The device features a global-chop mode
to remove offset drift over temperature and time.
Additionally, this device integrates offset and gain
calibration registers to help remove signal-chain
errors.
A low-drift, 1.2-V reference and precision oscillator
are integrated into the device reducing printed circuit
board (PCB) area. Optional cyclic redundancy checks
(CRCs) on the data input, data output, and register
map maintain communication integrity.
The complete analog front-end (AFE) is offered in
a 20-pin TSSOP package and is specified over the
automotive temperature range of –40°C to +125°C.
Device Information(1)
PART NUMBER
ADS131B02-Q1
(1)
PACKAGE
TSSOP (20)
BODY SIZE (NOM)
6.50 mm × 4.40 mm
For all available packages, see the orderable addendum at
the end of the data sheet.
AVDD
DVDD
1.2-V
Reference
Oscillator
Clock
Selection
CLKIN
SYNC/RESET
AIN0P
+
'6 ADC
AIN0N
Digital Filter
±
Gain & Offset
Calibration
CS
SCLK
Control &
Serial Interface
DIN
DOUT
AIN1P
+
'6 ADC
AIN1N
±
AGND
Digital Filter
Gain & Offset
Calibration
DRDY
DGND
Simplified Block Diagram
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
ADS131B02-Q1
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SBASAA3 – SEPTEMBER 2021
Table of Contents
1 Features............................................................................1
2 Applications..................................................................... 1
3 Description.......................................................................1
4 Revision History.............................................................. 2
5 Pin Configuration and Functions...................................3
6 Specifications.................................................................. 4
6.1 Absolute Maximum Ratings ....................................... 4
6.2 ESD Ratings .............................................................. 4
6.3 Recommended Operating Conditions ........................5
6.4 Thermal Information ...................................................5
6.5 Electrical Characteristics ............................................6
6.6 Timing Requirements ................................................. 8
6.7 Switching Characteristics ...........................................8
6.8 Timing Diagrams......................................................... 9
6.9 Typical Characteristics.............................................. 10
7 Parameter Measurement Information.......................... 12
7.1 Noise Measurements................................................ 12
8 Detailed Description......................................................13
8.1 Overview................................................................... 13
8.2 Functional Block Diagram......................................... 13
8.3 Feature Description...................................................14
8.4 Device Functional Modes..........................................23
8.5 Programming............................................................ 27
8.6 Register Map.............................................................37
9 Application and Implementation.................................. 53
9.1 Application Information............................................. 53
9.2 Typical Application.................................................... 56
10 Power Supply Recommendations..............................59
10.1 CAP Pin Capacitor Requirement............................ 59
10.2 Power-Supply Sequencing......................................59
10.3 Power-Supply Decoupling.......................................59
11 Layout........................................................................... 59
11.1 Layout Guidelines................................................... 59
11.2 Layout Example...................................................... 60
12 Device and Documentation Support..........................61
12.1 Receiving Notification of Documentation Updates..61
12.2 Support Resources................................................. 61
12.3 Trademarks............................................................. 61
12.4 Electrostatic Discharge Caution..............................61
12.5 Glossary..................................................................61
13 Mechanical, Packaging, and Orderable
Information.................................................................... 61
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
DATE
September 2021
2
REVISION
*
NOTES
Initial Release
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5 Pin Configuration and Functions
AVDD
1
20
DVDD
AGND
2
19
DGND
AIN0P
3
18
CAP
AIN0N
4
17
CLKIN
AIN1N
5
16
DIN
AIN1P
6
15
DOUT
NC
7
14
SCLK
NC
8
13
DRDY
NC
9
12
CS
NC
10
11
SYNC/RESET
Not to scale
Figure 5-1. PW Package, 20-Pin TSSOP, Top View
Table 5-1. Pin Functions
PIN
NAME
NO.
DESCRIPTION(1)
TYPE
AGND
2
Supply
AIN0N
4
Analog input
Negative analog input 0
AIN0P
3
Analog input
Positive analog input 0
AIN1N
5
Analog input
Negative analog input 1
AIN1P
6
Analog input
Positive analog input 1
AVDD
1
Supply
CAP
18
Analog output
CLKIN
17
Digital input
External clock input
CS
12
Digital input
Chip select; active low
DGND
19
Supply
DIN
16
Digital input
DOUT
15
Digital output
Serial data output
DRDY
13
Digital output
Data ready; active low
DVDD
Analog ground
Analog supply. Connect a 1-µF capacitor to AGND.
Digital low-dropout (LDO) regulator output.
Connect a 220-nF capacitor to DGND.
Digital ground
Serial data input
20
Supply
7, 8, 9, 10
-
SCLK
14
Digital input
Serial data clock
SYNC/RESET
11
Digital input
Conversion synchronization or system reset; active low
NC
(1)
Digital I/O supply. Connect a 1-µF capacitor to DGND.
Leave unconnected or connect to AGND
See the Unused Inputs and Outputs section for details on how to connect unused pins.
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6 Specifications
6.1 Absolute Maximum Ratings
See (1)
Power-supply voltage
MIN
MAX
AVDD to AGND
–0.3
3.9
AGND to DGND
–0.3
0.3
DVDD to DGND
–0.3
3.9
CAP to DGND
–0.3
2.2
UNIT
V
Analog input voltage
AINxP, AINxN
AGND – 1.6
AVDD + 0.3
V
Digital input voltage
CS, CLKIN, DIN, SCLK, SYNC/RESET
DGND – 0.3
DVDD + 0.3
V
Input current
Continuous, all pins except power-supply pins
Temperature
(1)
–10
10
Junction, TJ
150
Storage, Tstg
–60
150
mA
°C
Operation outside the Absolute Maximum Ratings may cause permanent device damage. Absolute Maximum Ratings do not imply
functional operation of the device at these or any other conditions beyond those listed under Recommended Operating Conditions.
If used outside the Recommended Operating Conditions but within the Absolute Maximum Ratings, the device may not be fully
functional, and this may affect device reliability, functionality, performance, and shorten the device lifetime.
6.2 ESD Ratings
VALUE
V(ESD)
(1)
4
Electrostatic discharge
Human-body model (HBM),
per AEC Q100-002(1)
HBM ESD classification level 2
Charged-device model (CDM),
per AEC Q100-011
CDM ESD classification level C4B
UNIT
±2000
Corner pins
±750
All other non-corner pins
±500
V
AEC Q100-002 indicates that HBM stressing shall be in accordance with the ANSI/ESDA/JEDEC JS-001 specification.
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6.3 Recommended Operating Conditions
over operating ambient temperature range (unless otherwise noted)
MIN
NOM
MAX
AVDD to AGND
2.7
3.3
3.6
AGND to DGND
–0.3
0
0.3
DVDD to DGND
2.7
3.3
3.6
UNIT
POWER SUPPLY
Analog power supply
Digital power supply
V
V
ANALOG INPUTS(1)
VAINxP,
VAINxN
Absolute input voltage
VIN
Differential input voltage
Gain = 1, 2
AGND – 0.1
AVDD – 1.2
Gain = 4, 8, 16, 32, 64, 128
AGND – 0.3
AVDD – 2.4
VIN = VAINxP - VAINxN
–VREF / Gain
VREF / Gain
V
V
EXTERNAL CLOCK SOURCE(2)
fCLKIN
External clock frequency
High-resolution mode
0.3
8.192
8.2
Low-power mode
0.3
4.096
4.15
0.3
2.048
2.08
40%
50%
60%
Very-low-power mode
Duty cycle
MHz
DIGITAL INPUTS
Input voltage
DGND
DVDD
V
–40
125
°C
TEMPERATURE
TA
(1)
(2)
Operating ambient temperature
The subscript "x" signifies the channel. For example, the positive analog input of channel 0 is named AIN0P. See the Pin Configuration
and Functions section for the pin names.
An external clock is not required when the internal oscillator is used.
6.4 Thermal Information
ADS131B02-Q1
THERMAL
METRIC(1)
PW (TSSOP)
UNIT
20 PINS
RθJA
91.5
°C/W
RθJC(top) Junction-to-case (top) thermal resistance
31.4
°C/W
RθJB
Junction-to-board thermal resistance
43.0
°C/W
ΨJT
Junction-to-top characterization parameter
2.0
°C/W
ΨJB
Junction-to-board characterization parameter
42.5
°C/W
RθJC(bot) Junction-to-case (bottom) thermal resistance
N/A
°C/W
(1)
Junction-to-ambient thermal resistance
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report.
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6.5 Electrical Characteristics
minimum and maximum specifications apply from TA = –40°C to +125°C; typical specifications are at TA = 25°C; all
specifications are at AVDD = 3.3 V, DVDD = 3.3 V, external clock, fCLKIN = 8.192 MHz, high-resolution mode, all channels, all
gains, data rate = 4 kSPS, all channels enabled, and global-chop mode disabled (unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
ANALOG INPUTS
Zin
Global-chop disabled
25
Differential input impedance Global-chop enabled
300
All power modes, all data rates
Absolute input current
Differential input current
MΩ
See Table 8-2
Global-chop disabled, VAINxP = VAINxN = 0 V
±1
Global-chop enabled, VAINxP = VAINxN = 0 V
±1
Global-chop disabled, VAINxP = VAINxN = 0 V
±50
Global-chop enabled, VAINxP = VAINxN = 0 V
±30
nA
pA
ADC CHARACTERISTICS
Resolution
24
Gain settings
1, 2, 4, 8, 16, 32, 64, 128
High-resolution mode, fCLKIN = 8.192 MHz
fDATA
Data rate
Bits
250
32k
Low-power mode, fCLKIN = 4.096 MHz
125
16k
Very-low-power mode, fCLKIN = 2.048 MHz
62.5
8k
SPS
ADC PERFORMANCE
INL
Integral nonlinearity (best fit) Differential-ended input
Offset error (input referred)
Global-chop disabled
–800
±200
800
Global-chop enabled
–4
±0.4
4
Global-chop disabled, gain = 1 to 4
Offset drift
Offset error long-term drift
Gain error
Gain drift
Gain error long-term drift
CMRR
6
Common-mode rejection
ratio
ppm of
FSR
10
100
500
Global-chop disabled, gain = 8 to 128
50
200
Global-chop enabled
10
30
1000 hours at TA = 85°C, global-chop
disabled
0.8
1000 hours at TA = 85°C, global-chop
enabled
0.25
Including error of internal voltage reference,
TA = 25°C
µV
nV/°C
μV
–0.7%
±0.2%
0.7%
Including drift of internal voltage reference,
TA = –40°C to +85°C, gain = 1 to 4
8
30
Including drift of internal voltage reference,
TA = –40°C to +85°C, gain = 8 to 128
7
25 ppm/°C
Including drift of internal voltage reference,
TA = –40°C to +125°C
13
1000 hours at TA = 85°C, gain = 1,
including drift of internal voltage reference
250
At dc, global-chop disabled, gain = 1
96
At dc, global-chop enabled, gain = 1
128
fCM = 50 Hz or 60 Hz, global-chop disabled,
gain = 1
89
fCM = 50 Hz or 60 Hz, global-chop enabled,
gain = 1
106
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dB
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6.5 Electrical Characteristics (continued)
minimum and maximum specifications apply from TA = –40°C to +125°C; typical specifications are at TA = 25°C; all
specifications are at AVDD = 3.3 V, DVDD = 3.3 V, external clock, fCLKIN = 8.192 MHz, high-resolution mode, all channels, all
gains, data rate = 4 kSPS, all channels enabled, and global-chop mode disabled (unless otherwise noted)
PARAMETER
PSRR
Power-supply rejection ratio
Input-referred noise
TEST CONDITIONS
MIN
AVDD at dc, global-chop disabled, gain = 1
81
AVDD at dc, global-chop enabled, gain = 1
116
DVDD at dc, global-chop disabled, gain = 1
109
DVDD at dc, global-chop enabled, gain = 1
117
Gain = 1
5.42
Gain = 8
1.29
All gains, all data rates
MAX
UNIT
dB
µVRMS
See Table 7-1
During fast start-up
Crosstalk
TYP
1.5
fIN = 50 Hz or 60 Hz
mVRMS
–120
dB
1.2
V
INTERNAL VOLTAGE REFERENCE
VREF
Internal reference voltage
INTERNAL OSCILLATOR
fOSC
Frequency
8.192
Accuracy
Frequency long-term drift
–5%
1000 hours at TA = 85°C
±0.5%
MHz
2.5%
0.2%
DIGITAL INPUTS/OUTPUTS
VIL
Logic input level, low
VIH
Logic input level, high
VOL
Logic output level, low
IOL = –1 mA
VOH
Logic output level, high
IOH = 1 mA
IIN
Input current
DGND < VDigital Input < DVDD
DGND
0.2 DVDD
V
0.8 DVDD
DVDD
V
0.2 DVDD
V
0.8 DVDD
V
–1
1
µA
POWER SUPPLY
IAVDD
Analog supply current
IDVDD
Digital supply current(1)
High-resolution mode, gain = 1, 2
2.9
3.6
High-resolution mode, gain = 4 to 128
3.3
4.2
Low-power mode, gain = 1, 2
1.5
2
Low-power mode, gain = 4 to 128
1.7
Very-low-power mode, gain = 1, 2
0.8
Very-low-power mode, gain = 4 to 128
0.9
Standby mode
0.4
Internal oscillator
140
High-resolution mode
0.3
Low-power mode
Very-low-power mode
Standby mode(2)
PD
Power dissipation
µA
0.4
0.15
0.2
0.1
0.14
1.2
mA
µA
10.6
13.2
High-resolution mode, gain = 4 to 128
11.9
15.2
5.4
7.3
3
4.4
Very-low-power mode, gain = 1, 2
(1)
(2)
1.2
High-resolution mode, gain = 1, 2
Low-power mode, gain = 1, 2
mA
mW
Currents measured with SPI idle.
External clock stopped.
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6.6 Timing Requirements
over operating ambient temperature range, and DOUT load = 20 pF || 100 kΩ (unless otherwise noted)
MIN
MAX
UNIT
2.7 V ≤ DVDD ≤ 3.6 V
tw(CLL)
Pulse duration, CLKIN low
49
ns
tw(CLH)
Pulse duration, CLKIN high
49
ns
tc(SC)
SCLK period
40
ns
tw(SCL)
Pulse duration, SCLK low
20
ns
tw(SCH)
Pulse duration, SCLK high
20
ns
tw(CSH)
Pulse duration, CS high
15
ns
td(CSSC)
Delay time, first SCLK rising edge after CS falling edge
16
ns
td(SCCS)
Delay time, CS rising edge after final SCLK falling edge
10
ns
tsu(DI)
Setup time, DIN valid before SCLK falling edge
5
ns
th(DI)
Hold time, DIN valid after SCLK falling edge
8
ns
tsu(SY)
Setup time, SYNC/RESET valid before CLKIN rising edge
tw(SYL)
Pulse duration, SYNC/RESET low for synchronization
tw(RSL)
Pulse duration, SYNC/RESET low to generate device reset
10
ns
1
2047
2048
tMCLK
tMCLK
6.7 Switching Characteristics
over operating ambient temperature range, and DOUT load = 20 pF || 100 kΩ (unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
2.7 V ≤ DVDD ≤ 3.6 V
tp(CSDO)
Propagation delay time, CS falling edge to
DOUT driven
50
ns
tp(SCDO)
Progapation delay time, SCLK rising edge to
valid new DOUT
20
ns
tp(CSDOZ)
Propagation delay time, CS rising edge to
DOUT high impedance
75
ns
tw(DRH)
Pulse duration, DRDY high
4
tMCLK
tw(DRL)
Pulse duration, DRDY low
4
tMCLK
SPI timeout
tPOR
Power-on-reset time
32768
Measured from supplies at 90%
to first DRDY rising edge
tREGACQ Register default acquisition time
8
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tMCLK
250
µs
5
µs
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6.8 Timing Diagrams
tw(CLH)
tw(CLL)
CLKIN
tw(DRL)
DRDY
tw(DRH)
§
CS
tw(SCL)
td(CSSC)
td(SCCS)
tc(SC)
tw(SCH)
tw(CSH)
§
SCLK
tsu(DI)
th(DI)
§ §
DIN
tp(CSDO)
tp(SCDO)
MSB - 1
tw(CSDOZ)
§ §
MSB
DOUT
LSB + 1
LSB
SPI settings are CPOL = 0 and CPHA = 1. CS transitions must take place when SCLK is low.
Figure 6-1. SPI Timing Diagram
§
CLKIN
tsu(SY)
tw(SYL)
tw(RSL)
§
SYNC/RESET
Figure 6-2. SYNC/RESET Timing Requirements
Supplies
90%
tPOR
DRDY
Figure 6-3. Power-On-Reset Timing
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6.9 Typical Characteristics
at TA = 25°C, AVDD = 3.3 V, DVDD = 3.3 V, fCLKIN = 8.192 MHz, data rate = 4 kSPS, and gain = 1 (unless otherwise noted)
4
Channel 0
Channel 1
200
100
0
-100
-200
-300
-40
-20
0
20
40
60
80
Temperature (°C)
100
120
Offset Error (input referred) (V)
Offset Error (input referred) (V)
300
3
2
1
0
-1
-2
-3
Channel 0
Channel 1
-4
-40
140
-20
Gain = 8, global-chop mode disabled
100
120
140
4
Gain = 1
Gain = 4
Gain = 8
Gain = 16
200
100
0
-100
-200
-20
0
20
40
60
80
Temperature (°C)
100
120
Offset Error (input referred) (PV)
Offset Error (input referred) (PV)
40
60
80
Temperature (°C)
Figure 6-5. Offset Error vs Temperature
300
3
2
1
0
-1
-2
Gain = 1
Gain = 4
Gain = 8
Gain = 16
-3
-4
-40
140
-20
0
Global-chop mode disabled
20
40
60
80
Temperature (°C)
100
120
140
Global-chop mode enabled
Figure 6-6. Offset Error vs Temperature
Figure 6-7. Offset Error vs Temperature
0
0.5
Gain = 1
Gain = 4
Gain = 8
Gain = 16
0.4
-50
Gain Error (ppm)
0.3
0.2
Gain Error (%)
20
Gain = 8, global-chop mode enabled
Figure 6-4. Offset Error vs Temperature
-300
-40
0
0.1
0
-0.1
-0.2
-100
-150
-200
-0.3
-250
-0.4
-0.5
-40
0
-20
0
20
40
60
80
Temperature (°C)
100
120
140
100
200
300
400 500 600
Time (hours)
700
800
900 1000
Gain = 1, including error of internal voltage reference
Including error of internal voltage reference
Figure 6-8. Gain Error vs Temperature
10
Figure 6-9. Gain Error Long-Term Drift
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6.9 Typical Characteristics (continued)
at TA = 25°C, AVDD = 3.3 V, DVDD = 3.3 V, fCLKIN = 8.192 MHz, data rate = 4 kSPS, and gain = 1 (unless otherwise noted)
Oscillator Frequency Error (%)
3
2
1
0
-1
-2
-3
-40
-20
0
20
40
60
80
Temperature (°C)
100
120
140
Gain = 8, global-chop mode disabled
Figure 6-10. Input-referred Noise vs Temperature
Figure 6-11. Oscillator Frequency Error vs Temperature
5
HR Mode
LP Mode
VLP Mode
4
3
2
1
0
-40
-20
0
20
40
60
80
Temperature (°C)
100
120
140
Analog Supply Current (mA)
Analog Supply Current (mA)
5
HR Mode
LP Mode
VLP Mode
4
3
2
1
0
-40
Gain = 1, OSR = 1024, all two ADC channels enabled
Figure 6-12. Analog Supply Current vs Temperature
20
40
60
80
Temperature (°C)
100
120
140
Figure 6-13. Analog Supply Current vs Temperature
6
HR Mode
LP Mode
VLP Mode
0.4
0.3
0.2
IAVDD
IDVDD
5
Supply Current (PA)
Digital Supply Current (mA)
0
Gain = 8, OSR = 1024, all two ADC channels enabled
0.6
0.5
-20
4
3
2
0.1
1
0
-40
-20
0
20
40
60
80
Temperature (°C)
100
120
140
0
-40
-20
OSR = 1024
0
20
40
60
80
Temperature (°C)
100
120
140
Standby mode
Figure 6-14. Digital Supply Current vs Temperature
Figure 6-15. Supply Current vs Temperature
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7 Parameter Measurement Information
7.1 Noise Measurements
Adjust the data rate and gain to optimize the ADS131B02-Q1 noise performance. When averaging is increased
by reducing the data rate, noise drops correspondingly. Table 7-1 summarizes the ADS131B02-Q1 noise
performance using the 1.2-V internal reference and a 3.3-V analog power supply. The data are representative of
typical noise performance at TA = 25°C when fMCLK = 8.192 MHz. The modulator clock frequency fMOD = fMCLK /
2. The data shown are typical input-referred noise results with the analog inputs shorted together and taking
an average of multiple readings across all channels. A minimum 1 second of consecutive readings are used to
calculate the RMS noise for each reading. Table 7-2 shows the effective resolution calculated from the noise
data. Equation 1 calculates effective resolution. In each case, VREF corresponds to the internal 1.2-V reference.
In global-chop mode, noise is improved by a factor of √2.
The noise performance scales with the oversampling rate (OSR) and gain settings, but is independent from the
configured power mode. Thus, the device exhibits the same noise performance in different power modes when
selecting the same OSR and gain settings. However, the data rate at the OSR settings scales based on the main
clock frequency for the different power modes.
§ 2 u VREF ·
Effective Resolution = log2 ¨
¸
© Gain u VRMS ¹
(1)
Table 7-1. Noise (μVRMS) at TA = 25°C
GAIN
OSR
DATA RATE (kSPS),
fMCLK = 8.192 MHz
1
2
4
8
16
32
64
128
16384
0.25
1.78
1.59
1.58
0.44
0.43
0.42
0.42
0.42
8192
0.5
2.51
2.19
2.07
0.60
0.59
0.58
0.58
0.58
4096
1
3.41
2.97
2.84
0.82
0.81
0.80
0.80
0.80
2048
2
4.54
3.96
3.76
1.07
1.06
1.05
1.05
1.05
1024
4
5.42
4.74
4.52
1.29
1.28
1.27
1.27
1.27
512
8
8.15
6.91
6.50
1.82
1.81
1.80
1.80
1.80
256
16
13.02
10.33
9.37
2.61
2.56
2.53
2.53
2.53
128
32
23.12
16.45
13.64
4.02
3.73
3.63
3.63
3.63
Table 7-2. Effective Resolution at TA = 25°C
12
GAIN
OSR
DATA RATE (kSPS),
fMCLK = 8.192 MHz
1
2
4
8
16
32
64
128
16384
0.25
20.4
19.5
18.5
19.4
18.4
17.4
16.4
15.4
8192
0.5
19.9
19.1
18.1
18.9
18.0
17.0
16.0
15.0
4096
1
19.4
18.6
17.7
18.5
17.5
16.5
15.5
14.5
2048
2
19.0
18.2
17.3
18.1
17.1
16.1
15.1
14.1
1024
4
18.8
17.9
17.0
17.8
16.8
15.8
14.8
13.8
512
8
18.2
17.4
16.5
17.3
16.3
15.3
14.3
13.3
256
16
17.5
16.8
16.0
16.8
15.8
14.9
13.9
12.9
128
32
16.7
16.2
15.4
16.2
15.3
14.3
13.3
12.3
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8 Detailed Description
8.1 Overview
The ADS131B02-Q1 is a low-power, two-channel, simultaneous-sampling, 24-bit, delta-sigma (ΔΣ) analog-todigital converter (ADC) with a low-drift internal reference voltage. The dynamic range, size, feature set, and
power consumption are optimized for cost-sensitive applications requiring simultaneous sampling.
The ADS131B02-Q1 requires both analog and digital supplies. The analog power supply (AVDD – AGND) can
operate between 2.7 V and 3.6 V. An integrated negative charge pump allows absolute input voltages as low
as 0.3 V below AGND, which enables measurements of input signals varying around ground with a unipolar
power supply. The digital power supply (DVDD – DGND) can operate between 2.7 V and 3.6 V. The device
features a high input impedance programmable gain amplifier (PGA) with gains up to 128. The ADC receives its
reference voltage from an integrated 1.2-V reference. The device allows differential input voltages as large as
the reference. Three power-scaling modes allow designers to trade power consumption for noise performance.
Each channel on the ADS131B02-Q1 contains a digital decimation filter that demodulates the output of the ΔΣ
modulators. The filter enables data rates as high as 32 kSPS per channel in high-resolution mode. Offset and
gain calibration registers can be programmed to automatically adjust output samples for measured offset and
gain errors. The Functional Block Diagram provides a detailed diagram of the ADS131B02-Q1.
The device communicates via a serial peripheral interface (SPI)-compatible interface. Several SPI commands
and internal registers control the operation of the ADS131B02-Q1. Other devices can be added to the same
SPI bus by adding discrete CS control lines. The SYNC/RESET pin can be used to synchronize conversions
between multiple ADS131B02-Q1 devices as well as to maintain synchronization with external events.
8.2 Functional Block Diagram
AVDD
DVDD
1.2-V
Reference
Oscillator
Clock
Selection
CLKIN
SYNC/RESET
AIN0P
+
'6 ADC
AIN0N
Digital Filter
±
Gain & Offset
Calibration
CS
SCLK
Control &
Serial Interface
DIN
DOUT
AIN1P
+
AIN1N
±
'6 ADC
Digital Filter
Gain & Offset
Calibration
AGND
DRDY
DGND
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8.3 Feature Description
8.3.1 Input ESD Protection Circuitry
Basic electrostatic discharge (ESD) circuitry protects the ADS131B02-Q1 inputs from ESD and overvoltage
events in conjunction with external circuits and assemblies. Figure 8-1 shows a simplified representation of the
ESD circuit. The protection for input voltages exceeding AVDD can be modeled as a simple diode.
AVDD
AINnP
To analog inputs
AINnN
AVDD
Figure 8-1. Input ESD Protection Circuitry
The ADS131B02-Q1 has an integrated negative charge pump that allows for input voltages below AGND with a
unipolar supply. Consequently, shunt diodes between the inputs and AGND cannot be used to clamp excessive
negative input voltages. Instead, the same diode that clamps overvoltage is used to clamp undervoltage at the
reverse breakdown voltage. Take care to prevent input voltages or currents from exceeding the limits provided in
the Absolute Maximum Ratings table.
8.3.2 Input Multiplexer
Each channel of the ADS131B02-Q1 has a dedicated input multiplexer. The multiplexer controls which signals
are routed to the ADC channels. Configure the input multiplexer using the MUXn[1:0] bits in the CHn_CFG
register. The input multiplexer allows the following inputs to be connected to the ADC channel:
• The analog input pins corresponding to the given channel
• AGND, which is helpful for offset calibration
• Positive dc test signal
• Negative dc test signal
See the Internal Test Signals section for more information about the test signals. Figure 8-2 shows a diagram of
the input multiplexer on the ADS131B02-Q1.
MUXn[1:0] = 00
SW
To Positive
PGA Input
AINnP
MUXn[1:0] = 10
SW
MUXn[1:0] = 11
SW
+
DC Test
Signal
±
AGND
SW
SW
MUXn[1:0] = 01
SW
SW
SW
MUXn[1:0] = 01
MUXn[1:0] = 10
AINnN
To Negative
PGA Input
MUXn[1:0] = 00
Figure 8-2. Input Multiplexer
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8.3.3 Programmable Gain Amplifier (PGA)
Each channel of the ADS131B02-Q1 features an integrated programmable gain amplifier (PGA) that provides
gains of 1, 2, 4, 8, 16, 32, 64, and 128. The gains for all channels are individually controlled by the PGAGAINn
bits for each channel in the GAIN register.
Varying the PGA gain scales the differential full-scale input voltage range (FSR) of the ADC. Equation 2
describes the relationship between FSR and gain. Equation 2 uses the internal reference voltage, 1.2 V, as the
scaling factor without accounting for gain error caused by tolerance in the reference voltage.
FSR = ±1.2 V / Gain
(2)
Table 8-1 shows the corresponding full-scale ranges for each gain setting.
Table 8-1. Full-Scale Range
GAIN SETTING
FSR
1
±1.2 V
2
±600 mV
4
±300 mV
8
±150 mV
16
±75 mV
32
±37.5 mV
64
±18.75 mV
128
±9.375 mV
The input impedance of the ADS131B02-Q1 depends on three factors: the main clock frequency (fMCLK), the
selected OSR setting, and the global-chop mode setting. Table 8-2 shows typical input impedance values for
fMCLK = 8.192 MHz. The input impedance scales indirectly proportional with the MCLK frequency, which means
that at fMCLK = 4.096 MHz, the impedance values in Table 8-2 increase by a factor of 2. Minimize the output
impedance of the circuit that drives the ADS131B02-Q1 inputs to obtain the best possible gain error, INL, and
distortion performance.
Table 8-2. Input Impedance
(1)
OSR SETTING
(1)
INPUT IMPEDANCE
GLOBAL-CHOP DISABLED
GLOBAL-CHOP ENABLED
128
6 MΩ
40 MΩ
256
13 MΩ
75 MΩ
512
25 MΩ
150 MΩ
1024
25 MΩ
300 MΩ
2048
25 MΩ
600 MΩ
4096
25 MΩ
≥1 GΩ
8192
25 MΩ
≥1 GΩ
16384
25 MΩ
≥1 GΩ
fMCLK = 8.192 MHz, default global-chop delay setting.
8.3.4 Voltage Reference
The ADS131B02-Q1 uses an internally generated, low-drift, band-gap voltage to supply the reference for the
ADC. The reference has a nominal voltage of 1.2 V, allowing the differential input voltage to swing from –1.2 V to
1.2 V at Gain = 1. The reference circuitry starts up very quickly to accommodate the fast start-up feature of this
device. The device waits until after the reference circuitry is fully settled before generating conversion data.
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8.3.5 Internal Test Signals
The ADS131B02-Q1 features an internal analog test signal that is useful for troubleshooting and diagnosis.
A positive or negative dc test signal can be applied to the channel inputs through the input multiplexer. The
multiplexer is controlled through the MUXn[1:0] bits in the CHn_CFG register. The test signals are created by
internally dividing the reference voltage. The same signal is shared by all channels.
The test signal is nominally 2 / 15 × VREF. The test signal automatically adjusts its voltage level with the gain
setting such that the ADC always measures a signal that is 2 / 15 × VDiff Max. For example, at a gain of 1, this
voltage equates to 160 mV. At a gain of 2, this voltage is 80 mV.
8.3.6 Clocking
The ADS131B02-Q1 requires a main clock (MCLK) to operate. The main clock to the ADS131B02-Q1 is
provided in one of two ways, as shown in Figure 8-3: an external clock on the CLKIN pin or the internal oscillator.
The CLK_SEL bit in the CLOCK register selects the according main clock source for the device.
PWR[1:0]
CLK_SEL
'6 ADC
fOSC
8.192 MHz
÷ 1, 2 or 4
Internal Oscillator
0
fMOD
MUX
÷2
fMCLK
fMOD
1
CLKIN
Figure 8-3. Main Clock Selection Diagram
8.3.6.1 External Clock Using CLKIN Pin
By default, the ADS131B02-Q1 is configured to operate with an external clock, such as at power-up. An
LVCMOS clock must be provided at the CLKIN pin continuously when the ADS131B02-Q1 is running in normal
operation. The frequency of the clock can be scaled in conjunction with the power mode to provide a trade-off
between power consumption and noise performance.
The PWR[1:0] bits in the CLOCK register allow the device to be configured in one of three power modes:
high-resolution (HR), low-power (LP), or very-low-power (VLP). Changing the PWR[1:0] bits scales the internal
bias currents to achieve the expected power levels. Follow the guidance for the external clock frequency
provided in the Recommended Operating Conditions table corresponding to the intended power mode in order
for the device to perform according to the specification.
8.3.6.2 Internal Oscillator
The internal oscillator can be selected as the MCLK source by setting the CLK_SEL bit in the CLOCK register. At
device power-up, the internal oscillator is disabled by default.
As shown in Figure 8-3 and Table 8-3, the internal oscillator frequency (fOSC) is scaled using a clock divider to
provide the appropriate nominal main clock frequency (fMCLK) for the different power modes. Correspondingly,
the modulator clock frequency (fMOD) scales as well because fMOD = fMCLK / 2.
Table 8-3. Scaling of the Internal Oscillator Frequency Based on the Selected Power Mode
16
POWER MODE
CLOCK DIVIDER SETTING
fMCLK
fMOD
HR
1
8.192 MHz
4.096 MHz
LP
2
4.096 MHz
2.048 MHz
VLP
4
2.048 MHz
1.024 MHz
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To switch between a running CLKIN and the internal oscillator as the MCLK source, put the device in standby
mode to avoid creating glitches when switching the clock source because there are no clock sequencers in the
device. Likewise, put the device in standby mode before changing power modes because a change in power
mode changes the MCLK frequency based on the clock divider setting.
When always using the internal oscillator as the MCLK source, tie the CLKIN pin to DGND. Tying the CLKIN pin
to DGND avoids the need to enter standby mode when switching from an external clock to the internal oscillator
at power-up or after a reset.
8.3.7 ΔΣ Modulator
The ADS131B02-Q1 uses a delta-sigma (ΔΣ) modulator to convert the analog input voltage to a one's density
modulated digital bit-stream. The ΔΣ modulator oversamples the input voltage at a frequency many times greater
than the output data rate. The modulator frequency, fMOD, of the ADS131B02-Q1 is equal to half the main clock
frequency (that is, fMOD = fMCLK / 2).
The output of the modulator is fed back to the modulator input through a digital-to-analog converter (DAC) as a
means of error correction. This feedback mechanism shapes the modulator quantization noise in the frequency
domain to make the noise more dense at higher frequencies and less dense in the band of interest. The digital
decimation filter following the ΔΣ modulator significantly attenuates the out-of-band modulator quantization
noise, allowing the device to provide excellent dynamic range.
8.3.8 Digital Filter
The ΔΣ modulator bit-stream feeds into a digital filter. The digital filter is a linear phase, finite impulse response
(FIR), low-pass sinc-type filter that attenuates the out-of-band quantization noise of the ΔΣ modulator. The digital
filter demodulates the output of the ΔΣ modulator by averaging. The data passing through the filter is decimated
and downsampled, to reduce the rate at which data come out of the modulator (fMOD) to the output data rate
(fDATA). The decimation factor, defined as per Equation 3, is called the oversampling ratio (OSR).
OSR = fMOD / fDATA
(3)
The OSR is configurable and is set by the OSR[2:0] bits in the CLOCK register. There are eight OSR settings in
the ADS131B02-Q1, allowing eight different data rate settings for any given main clock frequency. Table 8-4 lists
the OSR settings and their corresponding output data rates for the nominal MCLK frequencies mentioned.
The OSR determines the amount of averaging of the modulator output in the digital filter and therefore also
the filter bandwidth. The filter bandwidth directly affects the noise performance of the ADC because lower
bandwidth results in lower noise, whereas higher bandwidth results in higher noise. See Table 7-1 for the noise
specifications for various OSR settings.
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Table 8-4. OSR Settings and Data Rates for Nominal Main Clock Frequencies
POWER MODE
NOMINAL fMCLK
HR
fMOD
8.192 MHz
LP
4.096 MHz
4.096 MHz
VLP
2.048 MHz
2.048 MHz
1.024 MHz
OSR
OUTPUT DATA RATE
128
32 kSPS
256
16 kSPS
512
8 kSPS
1024
4 kSPS
2048
2 kSPS
4096
1 kSPS
8192
500 SPS
16384
250 SPS
128
16 kSPS
256
8 kSPS
512
4 kSPS
1024
2 kSPS
2048
1 kSPS
4096
500 SPS
8192
250 SPS
16384
125 SPS
128
8 kSPS
256
4 kSPS
512
2 kSPS
1024
1 kSPS
2048
500 SPS
4096
250 SPS
8192
125 SPS
16384
62.5 SPS
8.3.8.1 Digital Filter Implementation
Figure 8-4 shows the digital filter implementation of the ADS131B02-Q1. The modulator bitstream feeds two
parallel filter paths, a sinc3 filter, and a fast-settling filter path.
OSR[2:0]
Sinc3 Regular Filter
Modulator
Bitstream
Power-up
or
Reset
0
MUX
Fast-Settling Filter
265 ” 1024
Sinc1 Averager
(OSR > 1024)
0
MUX
OSR[2:0]
1
Global
Chop
Logic
Calibration
Logic,
Gain scaling
1
PGA_GAINx[2:0]
OSR = 1024
Figure 8-4. Digital Filter Implementation
8.3.8.1.1 Fast-Settling Filter
When the ADCs start converting for the first time after power-up or a device reset, the ADS131B02-Q1 selects
the fast-settling filter to allow for settled output data generation with minimal latency. The fast-settling filter has
the characteristic of a first-order sinc filter (sinc1). After two conversions, the device switches to and remains in
the sinc3 filter path until the next time the device is powered down or reset.
The fast-settling filter exhibits wider bandwidth and less stop-band attenuation than the sinc3 filter. Consequently,
the noise performance when using the fast-settling filter is not as high as with the sinc3 filter. The first two
18
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samples available from the ADS131B02-Q1 after a supply ramp or reset have the noise performance and
frequency response corresponding to the fast-settling filter as specified in the Electrical Characteristics table,
whereas subsequent samples have the noise performance and frequency response consistent with the sinc3
filter. See the Fast Start-Up Behavior section for more details regarding the fast start-up capabilities of the
ADS131B02-Q1.
8.3.8.1.2 SINC3 and SINC3 + SINC1 Filter
The ADS131B02-Q1 selects the sinc3 filter path two conversions after power-up or device reset. For OSR
settings of 128 to 1024, the sinc3 filter output directly feeds into the global-chop and calibration logic. For OSR
settings of 2048 and higher, the sinc3 filter is followed by a sinc1 filter. As shown in Table 8-5, the sinc3 filter
operates at a fixed OSR of 1024 in this case while the sinc1 filter implements the additional OSRs of 2 to 16.
That means, when an OSR of 4096 (for example) is selected, the sinc3 filter operates at an OSR of 1024 and the
sinc1 filter at an OSR of 4.
The filter has infinite attenuation at integer multiples of the data rate except for integer multiples of fMOD. Like
all digital filters, the digital filter response of the ADS131B02-Q1 repeats at integer multiples of the modulator
frequency, fMOD. The data rate and filter notch frequencies scale with fMOD.
When possible, plan frequencies for unrelated periodic processes in the application for integer multiples of the
data rate such that any parasitic effect they have on data acquisition is effectively canceled by the notches of the
digital filter. Avoid frequencies near integer multiples of fMOD whenever possible because tones in these bands
can alias to the band of interest.
The sinc3 and sinc3 + sinc1 filters for a given channel require time to settle after a channel is enabled, the
channel multiplexer or gain setting is changed, or a resynchronization event occurs. Table 8-5 lists the settling
times of the sinc3 and sinc3 + sinc1 filters for each OSR setting. The ADS131B02-Q1 does not gate unsettled
data. Therefore, the host must account for the filter settling time and disregard unsettled data if any are read.
The data at the next DRDY falling edge after the filter settling time listed in Table 8-5 has expired can be
considered fully settled.
Table 8-5. Digital Filter Settling Times
OSR (Overall)
OSR (SINC3)
OSR (SINC1)
SETTLING TIME (tMOD)
128
128
N/A
432
256
256
N/A
816
512
512
N/A
1584
1024
1024
N/A
3120
2048
1024
2
6192
4096
1024
4
10288
8192
1024
8
18480
16384
1024
16
34864
8.3.8.2 Digital Filter Characteristic
Equation 4 calculates the z-domain transfer function of a sinc3 filter that is used for OSRs ranging from 128 to
1024:
3
H z
1
N1
Z
Z
N
1
(4)
where:
•
N is the OSR
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Equation 5 calculates the transfer function of a sinc3 filter in terms of the continuous-time frequency parameter f:
Npf
fMOD
sin
½H(f)½ =
N ´ sin
3
pf
fMOD
(5)
where:
•
N is the OSR
Figure 8-5 and Figure 8-6 show the digital filter response of the fast-settling filter and the sinc3 filter for OSRs
ranging from 128 to 1024. Figure 8-7 and Figure 8-8 compare the digital filter responses of the sinc3 filter at an
OSR of 1024 and sinc3 + sinc1 filter for an OSR of 4096.
0
0
-20
-1.5
-3
Magnitude (dB)
Magnitude (dB)
-40
-60
-80
-100
-7.5
-10.5
Fast-settling filter
Sinc3 filter
-140
Fast-settling filter
Sinc3 filter
-12
0
1
2
3
Frequency (fIN/fDATA)
4
5
Figure 8-5. Fast-Settling and Sinc3 Digital Filter
Response
0
0
-100
-140
0.5
-4
-6
-8
-10
-120
0.4
-2
Magnitude (dB)
-80
0.2
0.3
Frequency (fIN/fDATA)
0
-40
-60
0.1
Figure 8-6. Fast-Settling and Sinc3 Digital Filter
Response, Pass-Band Detail
Sinc3 filter (1024)
Sinc3 + Sinc1 filter
-20
Magnitude (dB)
-6
-9
-120
Sinc3 filter (1024)
Sinc3 + Sinc1 filter
-12
0
1
2
3
4
5
6
7
8
Frequency (fIN/fDATA)
9
10
11
12
Figure 8-7. Digital Filter Response for OSR = 1024
and OSR = 4096
20
-4.5
0
0.1
0.2
0.3
Frequency (fIN/fDATA)
0.4
0.5
Figure 8-8. Digital Filter Response for OSR = 1024
and OSR = 4096, Pass-Band Detail
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8.3.9 Calibration Registers
The calibration registers allow for the automatic computation of calibrated ADC conversion results from
preprogrammed values. The host can rely on the device to automatically correct for system gain and offset after
the error correction terms are programmed into the corresponding device registers. The measured calibration
coefficients must be store in external non-volatile memory and programmed into the registers each time the
ADS131B02-Q1 powers up or resets because the ADS131B02-Q1 registers are volatile.
The offset calibration registers are used to correct for system offset error, otherwise known as zero error.
Offset error corresponds to the ADC output when the input to the system is zero. The ADS131B02-Q1 corrects
for offset errors by subtracting the contents of the OCALn[23:0] register bits in the CHn_OCAL_MSB and
CHn_OCAL_LSB registers from the conversion result for that channel before being output. There are separate
CHn_OCAL_MSB and CHnOCAL_LSB registers for each channel, which allows separate offset calibration
coefficients to be programmed for each channel. The contents of the OCALn[23:0] bits are interpreted by the
device as 24-bit two's complement values, which is the same format as the ADC data.
The gain calibration registers are used to correct for system gain error. Gain error corresponds to the
deviation of gain of the system from its ideal value. The ADS131B02-Q1 corrects for gain errors by multiplying
the ADC conversion result by the value given by the contents of the GCALn[23:0] register bits in the
CHn_GCAL_MSB and CHn_GCAL_LSB registers before being output. There are separate CHn_GCAL_MSB
and CHn_GCAL_LSB registers for each channel, which allows separate gain calibration coefficients to be
programmed for each channel. The contents of the GCALn[23:0] bits are interpreted by the device as 24-bit
unsigned values corresponding to linear steps ranging from gains of 0 to 2 – (1 / 223). Table 8-6 describes the
relationship between the GCALn[23:0] bit values and the gain calibration factor.
Table 8-6. GCALn[23:0] Bit Mapping
GCALn[23:0] VALUE
GAIN CALIBRATION FACTOR
000000h
0
000001h
1.19 × 10–7
800000h
1
FFFFFEh
2 – 2.38 × 10–7
FFFFFFh
2 – 1.19 × 10–7
The calibration registers do not need to be enabled because they are always in use. The OCALn[23:0] bits have
a default value of 000000h resulting in no offset correction. Similarly, the GCALn[23:0] bits default to 800000h
resulting in a gain calibration factor of 1.
Figure 8-9 shows a block diagram illustrating the mechanics of the calibration registers on one channel of the
ADS131B02-Q1.
û
Modulator
Digital
Filter
To Interface
Å
1
OCALn[23:0]
223
GCALn[23:0]
Figure 8-9. Calibration Block Diagram
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8.3.10 Register Map CRC
The ADS131B02-Q1 performs a CRC on its own register map as a means to check for unintended changes
to the registers. Enable the register map CRC by setting the REG_CRC_EN bit in the MODE register. When
enabled, the device constantly calculates the register map CRC across the registers ranging from address 02h
to 12h including the reserved registers. The CRC is calculated beginning with the MSB of register 02h and
ending with the LSB of register 12h using the polynomial selected in the CRC_TYPE bit in the MODE register.
Two types of CRC polynomials are available: CCITT CRC and ANSI CRC (CRC-16). See Table 8-8 for details on
the CRC polynomials. The CRC calculation is initialized with the seed value of FFFFh.
The calculated CRC is a 16-bit value and is stored in the REGMAP_CRC register. The calculation is done
using one register map bit per MCLK period and constantly checks the result against the previous calculation.
The REG_MAP bit in the STATUS register is set to flag the host if the register map CRC changes, including
changes resulting from register writes. The REG_MAP bit is cleared by reading the STATUS register, or when
the STATUS register is output as a response to the NULL command.
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8.4 Device Functional Modes
Figure 8-10 shows a state diagram depicting the major functional modes of the ADS131B02-Q1 and the
transitions between these modes.
POR, pin reset, or
RESET command
Reset
complete
Reset
STANDBY
Standby
Mode
Continuous
Conversion Mode
WAKEUP && GC_EN
STANDBY
WAKEUP
&& GC_EN
GC_EN
GC_EN
Global Chop
Mode
Figure 8-10. State Diagram Depicting Device Functional Modes
8.4.1 Power-Up and Reset
The ADS131B02-Q1 is reset in one of three ways: by a power-on reset (POR), by the SYNC/RESET pin, or
by a RESET command. After a reset occurs, the configuration registers are reset to the default values and the
device begins generating conversion data as soon as a valid MCLK is provided. In all three cases a low to high
transition on the DRDY pin indicates that the SPI interface is ready for communication. The device ignores any
SPI communication before this point.
8.4.1.1 Power-On Reset
Power-on reset (POR) is the reset that occurs when a valid supply voltage is first applied. The POR process
requires tPOR to complete from when the supply voltages reach 90% of their nominal value to allow for the
internal circuitry to power up. The DRDY pin transitions from low to high immediately after tPOR indicating the SPI
interface is ready for communication.
8.4.1.2 SYNC/RESET Pin
The SYNC/RESET pin is an active low, dual-function pin that generates a reset if the pin is held low for longer
than tw(RSL). The device maintains a reset state until SYNC/RESET is returned high. The host must wait for at
least tREGACQ after SYNC/RESET is brought high or for the DRDY rising edge before communicating with the
device.
8.4.1.3 RESET Command
The ADS131B02-Q1 can be reset via the SPI RESET command. The device communicates in frames of a
fixed length. Four words are required to complete a frame on the ADS131B02-Q1. The RESET command
is transmitted in the first word of the data frame on DIN, but the command is not latched and executed by
the device until the entire frame is complete. Terminating the frame early causes the RESET command to be
ignored. A device reset occurs immediately after the RESET command is latched. The host must wait for at least
tREGACQ or for the DRDY rising edge before communicating with the device.
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8.4.2 Fast Start-Up Behavior
The ADS131B02-Q1 begins generating conversion data shortly after start-up as soon as a valid MCLK signal is
provided to the ΔΣ modulators. Fast start-up is accomplished via two mechanisms. First, the device internal
power-supply circuitry is designed specifically to enable fast start-up. Second, the digital decimation filter
dynamically switches from a fast-settling filter to a sinc3 filter when the sinc3 filter has settled.
After the supplies are ramped to 90% of their final values, the device requires tPOR for the internal circuitry to
settle. The end of tPOR is indicated by a transition of DRDY from low to high. The transition of DRDY from low to
high also indicates the SPI interface is ready to accept commands.
The ΔΣ modulators of the ADS131B02-Q1 require CLKIN to toggle after tPOR to begin working, or alternatively,
activate the internal oscillator by setting the CLK_SEL bit in the CLOCK register. The modulators begin sampling
the input signal after an initial wait time delay of (256 + 44) × tMOD when MCLK begins toggling. Therefore, when
using an external clock, provide a valid clock signal on CLKIN as soon as possible after the supply ramp to
achieve the fastest possible start-up time.
The data generated by the ΔΣ modulators are fed to the digital filter blocks. The data are provided to both the
fast-settling filter and the sinc3 filter paths. The fast-settling filter requires only one data rate period to provide
settled data. Meanwhile, the sinc3 filter requires three data rate periods to settle. The fast-settling filter generates
the output data for the two interim ADC output samples indicated by DRDY transitioning from high to low while
the sinc3 filter is settling. The device disables the fast-settling filter and provides conversion data from the sinc3
filter path for the third and following samples. Figure 8-11 shows the behavior of the fast-start-up feature when
using an external clock that is provided to the device right after the supplies have ramped. Table 8-7 shows the
values for the various start-up and settling times relevant to the device start-up.
Supplies
90%
tSETTLE3
tPOR
tDATA
tSETTLE1
tDATA
DRDY
Fast-settling
filter data
...
CLKIN
Sinc3
filter data
Fast-settling
filter data
...
...
Sinc3
filter data
...
Figure 8-11. Fast Start-Up Behavior and Settling Times
Table 8-7. Fast Start-Up Settling Times for Default OSR = 1024
VALUE (DETAILS)
(tMOD)
VALUE
(tMOD)
VALUE AT
fMCLK = 8.192 MHz (ms)
tDATA = 1/fDATA
1024
1024
0.250
tSETTLE1
256 + 44 + 1024
1324
0.323
tSETTLE3
256 + 44 + 3 × 1024
3372
0.823
PARAMETER
The fast-settling filter provides conversion data that are significantly noisier than the data that comes from the
sinc3 filter path, but allows the device to provide settled conversion data during the longer settling time of the
more accurate sinc3 digital filter. If the level of precision provided by the fast-settling filter is insufficient even for
the first samples immediately following start-up, ignore the first two instances of DRDY toggling from high to low
and begin collecting data on the third instance.
The start-up process following a RESET command or a pin reset using the SYNC/RESET pin is similar to what
occurs after power up. However there is no tPOR in the case of a command or pin reset because the supplies are
already ramped. After reset, the device waits for the initial wait time delay of (256 + 44) × tMOD before providing
modulator samples to the two digital filters. The fast-settling filter is enabled for the first two output samples.
Remember to enable the internal oscillator every time again after a reset in case the internal oscillator is to be
used, because the device defaults to using an external clock.
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8.4.3 Conversion Modes
There are two ADC conversion modes on the ADS131B02-Q1: continuous-conversion and global-chop mode.
Continuous-conversion mode is a mode where ADC conversions are generated constantly by the ADC at a
rate defined by fMOD / OSR. Global-chop mode differs from continuous-conversion mode because global-chop
periodically chops (or swaps) the inputs, which reduces system offset errors at the cost of settling time between
the points when the inputs are swapped. In either continuous-conversion or global-chop mode, there are three
power modes that provide flexible options to scale power consumption with bandwidth and dynamic range. The
Power Modes section discusses these power modes in further detail.
8.4.3.1 Continuous-Conversion Mode
Continuous-conversion mode is the mode in which ADC data are generated constantly at the rate of fDATA =
fMOD / OSR. New data are indicated by a DRDY falling edge at this rate. Continuous-conversion mode is
intended for measuring AC signals because this mode allows for higher output data rates than global-chop
mode.
8.4.3.2 Global-Chop Mode
The ADS131B02-Q1 incorporates a global-chop mode option to reduce offset error and offset drift inherent
to the device resulting from mismatch in the internal circuitry to very low levels. When global-chop mode
is enabled by setting the GC_EN bit in the GLOBAL_CHOP_CFG register, the device uses the conversion
results from two consecutive internal conversions taken with opposite input polarity to cancel the device offset
voltage. Conversion n is taken with normal input polarity. The device then reverses the internal input polarity for
conversion n + 1. The average of two consecutive conversions (n and n + 1, n + 1 and n + 2, and so on) yields
the final offset compensated result.
Figure 8-12 shows a block diagram of the global-chop mode implementation. The combined PGA and ADC
internal offset voltage is modeled as VOFS. Only this device inherent offset voltage is reduced by global-chop
mode. Offset in the external circuitry connected to the analog inputs is not affected by global-chop mode.
GC_EN
Chop Switch
VOFS
+ Digital
Filter
ADC
AINnP
PGA
ADC
Global-Chop
Mode Control
Conversion Output
AINnN
Figure 8-12. Global-Chop Mode Implementation
The conversion period in global-chop mode differs from the conversion time when global-chop mode is disabled
(tDATA = OSR × tMOD). Figure 8-13 shows the conversion timing for an ADC channel using global-chop mode.
Global-chop delay
Modulator sampling
Conversion
start
xx
Sampling
n
Data not
settled
Data not
settled
Sampling
n
Swap inputs,
digital filter reset
xx
Sampling
n
tGC_FIRST CONVERSION
Sampling
n+1
Data not
settled
Data not
settled
Sampling
n+1
st
nd
1 global-chop
conversion result
Sampling
n+1
x
Sampling
n+2
2 global-chop
conversion result
Sampling
n+2
tGC_CONVERSION
Sampling
n+2
Sampling
n+3
x
x
ADC overhead
Sampling
n+3
Sampling
n+3
tDATA
Figure 8-13. Conversion Timing With Global-Chop Mode Enabled
Every time the device swaps the input polarity, the digital filter is reset. The ADC then always takes three internal
conversions to produce one settled global-chop conversion result.
The ADS131B02-Q1 provides a programmable delay (tGC_DLY) between the end of the previous conversion
period and the beginning of the subsequent conversion period after the input polarity is swapped. This delay
allows for external input circuitry to settle because the chopping switches interface directly with the analog
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inputs. The GC_DLY[3:0] bits in the GLOBAL_CHOP_CFG register configure the delay after chopping the
inputs. The global-chop delay is selected in terms of modulator clock periods from 2 to 65,536 × tMOD.
The effective conversion period in global-chop mode follows Equation 6. A DRDY falling edge is generated each
time a new global-chop conversion becomes available to the host.
The conversion process of all ADC channels in global-chop mode is restarted in the following two conditions so
that all channels start sampling at the same time:
• Falling edge of SYNC/RESET pin
• Change of OSR setting
The conversion period of the first conversion after the ADC channels are reset is considerably longer than
the conversion period of all subsequent conversions mentioned in Equation 6, because the device first must
perform two fully settled internal conversions with the input polarity swapped. The conversion period for the first
conversion in global-chop mode follows Equation 7.
tGC_CONVERSION = tGC_DLY + 3 × OSR × tMOD
(6)
tGC_FIRST_CONVERSION = tGC_DLY + 3 × OSR × tMOD + tGC_DLY + 3 × OSR x tMOD + 44 × tMOD
(7)
Using global-chop mode reduces the ADC noise shown in Table 7-1 at a given OSR by a factor of √2 because
two consecutive internal conversions are averaged to yield one global-chop conversion result. The dc test signal
cannot be measured in global-chop mode.
8.4.4 Power Modes
In both continuous-conversion and global-chop mode, there are three selectable power modes that allow scaling
of power with bandwidth and performance: high-resolution (HR) mode, low-power (LP) mode, and very-lowpower (VLP) mode. The mode is selected by the PWR[1:0] bits in the CLOCK register. See the Clocking section
for restrictions on the CLKIN frequency for each power mode in case an external clock source is used, or how
the main clock frequency is scaled with each power mode in case the internal oscillator is enabled.
8.4.5 Standby Mode
Standby mode is a low-power state in which all channels are disabled, and the reference, internal oscillator and
other non-essential circuitry are powered down. This mode differs from completely powering down the device
because the device retains its register settings. Enter standby mode by sending the STANDBY command. Stop
toggling CLKIN when the device is in standby mode and an external clock is used to minimize device power
consumption. See the Clocking section for recommendations on how to use standby mode when switching
between internal and external clock generation. Exit standby mode by sending the WAKEUP command.
8.4.6 Synchronization
Synchronization can be performed by the host to make sure the ADC conversions are synchronized to an
external event. For example, synchronization can realign the data capture to the expected timing of the host if a
glitch on the clock causes the host and device to become out of synchronization.
The SYNC/RESET pin is a multifunction digital input pin that allows the host to synchronize conversions to an
external event or to reset the device. See the SYNC/RESET Pin section for more details regarding how the
device is reset.
Provide a negative pulse on the SYNC/RESET pin with a duration less than tw(RSL) but greater than a MCLK
period to trigger synchronization. The device internally compares the leading negative edge of the pulse to its
internal clock that tracks the data rate. The internal data rate clock has timing equivalent to the DRDY pin.
If the negative edge on SYNC/RESET aligns with the internal data rate clock, the device is determined to be
synchronized and therefore no action is taken. If there is misalignment, the digital filters on the device are reset
to be synchronized with the SYNC/RESET pulse.
In global-chop mode conversions are always immediately restarted at the falling edge of the SYNC/RESET pin.
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8.5 Programming
8.5.1 Serial Interface
The ADS131B02-Q1 uses an SPI-compatible interface to configure the device and retrieve conversion data. The
device always acts as an SPI peripheral; SCLK and CS are inputs to the interface. The interface operates in
SPI mode 1 where CPOL = 0 and CPHA = 1. In SPI mode 1, the SCLK idles low and data are launched or
changed only on SCLK rising edges; data are latched or read by the controller and peripheral on SCLK falling
edges. The interface is full-duplex, meaning data can be sent and received simultaneously by the interface. The
device includes the typical SPI signals: SCLK, CS, DIN (MOSI), and DOUT (MISO). In addition, there are two
other digital pins that provide additional functionality. The DRDY pin serves as a flag to the host to indicate
new conversion data are available. The SYNC/RESET pin is a dual-function pin that allows synchronization of
conversions to an external event and allows for a hardware device reset.
8.5.1.1 Chip Select (CS)
The CS pin is an active-low input signal that selects the device for communication. The device ignores any
communication and DOUT is high impedance when CS is held high. Hold CS low for the duration of a
communication frame to maintain proper communication. The interface is reset each time CS is taken high.
8.5.1.2 Serial Data Clock (SCLK)
The SCLK pin is an input that serves as the serial clock for the interface. Output data on the DOUT pin transition
on the rising edge of SCLK and input data on DIN are latched on the falling edge of SCLK.
8.5.1.3 Serial Data Input (DIN)
The DIN pin is the serial data input pin for the device. Serial commands are shifted in through the DIN pin by the
device with each SCLK falling edge when the CS pin is low.
8.5.1.4 Serial Data Output (DOUT)
The DOUT pin is the serial data output pin for the device. The device shifts out command responses and
ADC conversion data serially with each rising SCLK edge when the CS pin is low. This pin assumes a highimpedance state when CS is high.
8.5.1.5 Data Ready (DRDY)
The DRDY pin is an active-low digital output that indicates when new conversion data are available for readout.
Connect the DRDY pin to a digital input on the host to trigger periodic data retrieval in conversion mode.
A high-to-low transition of the DRDY output indicates that new conversion data completed and are ready for
readout. The period between DRDY falling edges is the data-rate period. A low level of the DRDY pin indicates
that the latest conversion data have not yet been read. DRDY transitions high when the conversion data of the
two ADC channels, including those of disabled channels, are shifted out of the device. DRDY stays low if the
data read is incomplete, thus indicating that not all ADC data have been retrieved. In case conversion data are
not read before the next conversion cycle completes, DRDY transitions high tw(DRH) ahead of the next DRDY
falling edge. See the Collecting Data for the First Time or After a Pause in Data Collection section for more
information about the behavior of DRDY when data are not consistently read. The DRDY high pulse is blocked
when new conversions complete while conversion data are read. Therefore, avoid reading ADC data during the
time where new conversions complete in order to achieve consistent DRDY behavior.
The DRDY_HIZ bit in the MODE register configures the state of the DRDY pin when deasserted. By default
the bit is 0b, meaning the pin is actively driven high using a push-pull output stage. When the bit is 1b, DRDY
behaves like an open-drain digital output. Use a 100-kΩ pullup resistor to pull the pin high when DRDY is not
asserted.
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8.5.1.6 SPI Communication Frames
SPI communication on the ADS131B02-Q1 is performed in frames. Each SPI communication frame consists
of several words. The word size is configurable as either 16 bits, 24 bits, or 32 bits by programming the
WLENGTH[1:0] bits in the MODE register.
The interface is full duplex, meaning that the interface is capable of transmitting data on DOUT while
simultaneously receiving data on DIN. The input frame that the host sends on DIN always begins with a
command. The first word on the output frame that the device transmits on DOUT always begins with the
response to the command that was written on the previous input frame. The number of words in a command
depends on the command provided. For most commands, there are four words in a frame. On DIN, the host
provides the command, the command CRC if input CRC is enabled or a word of zeros if input CRC is disabled,
and two additional words of zeros. Simultaneously on DOUT, the device outputs the response from the previous
frame command, two words of ADC data representing the two ADC channels, and a CRC word. Figure 8-14
shows a typical command frame structure.
DRDY
CS
SCLK
DIN
DOUT
Hi-Z
Command
CRC
Response
Channel 0 Data
Channel 1 Data
CRC
Hi-Z
Command
CRC
Response
Channel 0 Data
Figure 8-14. Typical Communication Frame
There are some commands that require more or less than words. In the case of a read register
(RREG) command where more than a single register is read, the response to the command contains the
acknowledgment of the command followed by the register contents requested, which may require a longer frame
depending on how many registers are read. See the RREG command section for more details on the RREG
command.
In the case of a write register (WREG) command where more than a single register is written, the frame
extends to accommodate the additional data. See the WREG command section for more details on the WREG
command.
See the Commands section for a list of all valid commands and their corresponding responses on the
ADS131B02-Q1.
Under special circumstances, a data frame can be shortened by the host. See the Short SPI Frames section for
more information about artificially shortening communication frames.
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8.5.1.7 SPI Communication Words
An SPI communication frame with the ADS131B02-Q1 is made of words. Words on DIN can contain commands,
register settings during a register write, or a CRC of the input data. Words on DOUT can contain command
responses, register settings during a register read, ADC conversion data, or CRC of the output data.
Words can be 16, 24, or 32 bits. The word size is configured by the WLENGTH[1:0] bits in the MODE register.
The device defaults to a 24-bit word size. Commands, responses, CRC, and registers always contain 16 bits of
actual data. These words are always most significant bit (MSB) aligned, and therefore the least significant bits
(LSBs) are zero-padded to accommodate 24- or 32-bit word sizes. ADC conversion data are nominally 24 bits.
The ADC truncates its eight LSBs when the device is configured for 16-bit communication. There are two options
for 32-bit communication available for ADC data that are configured by the WLENGTH[1:0] bits in the MODE
register. Either the ADC data can be LSB padded with zeros or the data can be MSB sign extended.
Figure 8-15 through Figure 8-18 show the locations of the individual bits in an SPI frame for the different word
size options using a WREG command frame for writing two registers as an example.
CS
DIN
WREG
15
Register Data 0
0
DOUT
15
Response
15
Register Data 1
0
15
Channel 0 Data
0
15
CRC
0
15
0
Channel 1 Data
0
CRC
0
15
0
15
Figure 8-15. SPI Frame using 16-bit Word Size
CS
DIN
WREG
23
DOUT
Register Data 0
8
0
23
Response
23
Register Data 1
8
0
23
Channel 0 Data
8
0
23
CRC
8
0
23
Channel 1 Data
0
0
23
8
0
8
0
CRC
23
Figure 8-16. SPI Frame using 24-bit Word Size
CS
DIN
WREG
31
DOUT
Register Data 0
16
0
Response
31
31
Sign ext.
16
0
31
Register Data 1
16
0
Channel 0 Data
24
31
Sign ext.
0
31
CRC
16
0
31
Channel 1 Data
24
16
0
16
0
16
0
16
0
CRC
0
31
Figure 8-17. SPI Frame using 32-bit, sign-extended Word Size
CS
DIN
WREG
31
DOUT
Register Data 0
16
0
31
Response
31
Register Data 1
16
0
31
Channel 0 Data
16
0
31
CRC
16
0
31
Channel 1 Data
8
0
31
CRC
8
0
31
Figure 8-18. SPI Frame using 32-bit, zero-padded Word Size
8.5.1.8 Short SPI Frames
The SPI frame can be shortened to only send commands and receive responses if the ADCs are disabled and
no ADC data are being output by the device. Read out all expected output data words from each sample period
if the ADCs are enabled. Reading all of the data output with each frame provides predictable DRDY pin behavior.
If reading out all the data on each output data period is not feasible, see the Collecting Data for the First Time or
After a Pause in Data Collection section on how to begin reading data again after a pause from when the ADCs
were last enabled.
A short frame is not possible when using the RESET command. A full frame must be provided for a device reset
to take place when sending the RESET command.
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8.5.1.9 Communication Cyclic Redundancy Check (CRC)
The ADS131B02-Q1 features a cyclic redundancy check (CRC) engine on both input and output data to mitigate
SPI communication errors. The CRC word is 16 bits wide for either input or output CRC. Coverage includes all
words in the SPI frame where the CRC is enabled, including zero-padded or sign-extended bits.
CRC on the SPI input is optional and can be enabled and disabled by writing the RX_CRC_EN bit in the MODE
register. Input CRC is disabled by default. When the input CRC is enabled, the device checks the provided
input CRC against the CRC generated based on the input data. A CRC error occurs if the CRC words do not
match. The device does not execute any commands, except for the WREG command, if the input CRC check
fails. A WREG command always executes even when the CRC check fails. The device sets the CRC_ERR bit
in the STATUS register for all cases of a CRC error. The response on the output in the SPI frame following the
frame where the CRC error occurred is that of a NULL command, which means the STATUS register plus the
conversion data are output in the following SPI frame. The CRC_ERR bit is cleared when the STATUS register is
output.
The output CRC cannot be disabled and always appears at the end of the output frame. The host can ignore the
data if the output CRC is not used.
There are two types of CRC polynomials available: CCITT CRC and ANSI CRC (CRC-16). The CRC setting
determines the algorithm for both the input and output CRC. The CRC type is programmed by the CRC_TYPE
bit in the MODE register. Table 8-8 lists the details of the two CRC types. The CRC calculation is initialized with
the seed value of FFFFh to detect errors in the event that DIN or DOUT are stuck low.
Table 8-8. CRC Types
CRC TYPE
CCITT CRC
ANSI CRC
POLYNOMIAL
x16
+
x12
+
x5
BINARY POLYNOMIAL
+1
0001 0000 0010 0001
x16 + x15 + x2 + 1
1000 0000 0000 0101
8.5.1.10 SPI Timeout
The ADS131B02-Q1 features an SPI timeout as a means to recover SPI communication, especially in situations
where CS is permanently tied low. Enable the SPI timeout using the TIMEOUT bit in the MODE register. When
enabled, the entire SPI frame (first SCLK to last SCLK) must complete in 215 MCLK cycles, otherwise the SPI
logic will reset. When a timeout happens the device starts interpreting the data starting with the next SCLK as a
new SPI frame.
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8.5.2 ADC Conversion Data Format
The device provides conversion data for each channel at the data rate. All data are available immediately
following DRDY assertion. The conversion status of all channels is available as the DRDY[1:0] bits in the
STATUS register. The STATUS register content is automatically output as the response to the NULL command.
Conversion data are 24 bits. The data LSBs are truncated when the device operates with a 16-bit word size.
The LSBs are zero padded or the MSBs sign extended when operating with a 32-bit word size depending on the
setting of the WLENGTH[1:0] bits in the MODE register.
Data are given in binary two's complement format. Use Equation 8 to calculate the size of one code (LSB).
1 LSB = (2.4 / Gain) / 224 = +FSR / 223
(8)
A positive full-scale input VIN ≥ +FSR – 1 LSB = 1.2 / Gain – 1 LSB produces an output code of 7FFFFFh and
a negative full-scale input (VIN ≤ –FSR = –1.2 / Gain) produces an output code of 800000h. The output clips at
these codes for signals that exceed full-scale.
Table 8-9 summarizes the ideal output codes for different input signals.
Table 8-9. Ideal Output Code versus Input Signal
INPUT SIGNAL
(VIN = VAINP – VAINN)
IDEAL OUTPUT CODE
≥ FSR (223 – 1) / 223
7FFFFFh
223
FSR /
000001h
0
000000h
–FSR /
223
FFFFFFh
≤ –FSR
800000h
Figure 8-19 shows the mapping of the analog input signal to the output codes.
7FFFFFh
000001h
000000h
FFFFFFh
¼
Output Code
¼
7FFFFEh
800001h
800000h
¼
-FS
2
23
FS
¼
-1
-FS
2
0
Input Voltage VIN
23
2
23
FS
2
-1
23
Figure 8-19. Code Transition Diagram
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8.5.3 Commands
Table 8-10 contains a list of all valid commands, a short description of their functionality, their binary command
word, and the expected response that appears in the following frame.
Table 8-10. Command Definitions
COMMAND
NULL
RESET
(2)
DESCRIPTION
RESPONSE
0000 0000 0000 0000
STATUS register
Reset the device
0000 0000 0001 0001
1111 1111 0100 0010
STANDBY
Place the device into standby mode
0000 0000 0010 0010
0000 0000 0010 0010
WAKEUP
Wake the device from standby mode to conversion mode
0000 0000 0011 0011
0000 0000 0011 0011
LOCK
Lock the interface such that only the NULL, UNLOCK, and
RREG commands are valid
0000 0101 0101 0101
0000 0101 0101 0101
Unlock the interface after the interface is locked
0000 0110 0101 0101
0000 0110 0101 0101
UNLOCK
(1)
COMMAND WORD
No operation
RREG
Read nnn nnnn plus 1 registers beginning at address a aaaa a
101a aaaa annn nnnn
dddd dddd dddd dddd
or
111a aaaa annn nnnn (1)
WREG
Write nnn nnnn plus 1 registers beginning at address a aaaa a
011a aaaa annn nnnn
010a aaaa ammm mmmm (2)
When nnn nnnn is 0, the response is the requested register data dddd dddd dddd dddd. When nnn nnnn is greater than 0, the
response begins with 111a aaaa annn nnnn, followed by the register data.
In this case, mmm mmmm represents the number of registers that are actually written minus one. This value may be less than nnn
nnnn in some cases.
8.5.3.1 NULL (0000 0000 0000 0000)
The NULL command is the no-operation command that results in no registers read or written, and the state of
the device remains unchanged. The intended use case for the NULL command is to read out ADC conversion
data. The command response for the NULL command is the contents of the STATUS register. Any invalid
command also gives the NULL response.
8.5.3.2 RESET (0000 0000 0001 0001)
The RESET command resets the ADC to its register defaults. The command is latched by the device at the
end of the frame. A reset occurs immediately after the command is latched. The host must wait for tREGACQ
after reset or for the DRDY rising edge before communicating with the device to make sure the registers have
assumed their default settings. The device sends an acknowledgment of FF42h when the ADC is properly
RESET. The device responds with 0011h if the command word is sent but the frame is not completed and
therefore the device is not reset. See the RESET Command section for more information regarding the operation
of the reset command. Figure 8-20 illustrates a properly sent RESET command frame.
32
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CS
SCLK
DIN
RESET
CRC
RESET command
latched here
DOUT
Hi-Z
Response
'RQ¶W &DUH
'RQ¶W &DUH
'RQ¶W &DUH
Hi-Z
Figure 8-20. RESET Command Frame
8.5.3.3 STANDBY (0000 0000 0010 0010)
The STANDBY command places the device in a low-power standby mode. The command is latched by the
device at the end of the frame. The device enters standby mode immediately after the command is latched.
See the Standby Mode section for more information. This command has no effect when the device is already in
standby mode.
8.5.3.4 WAKEUP (0000 0000 0011 0011)
The WAKEUP command returns the device to conversion mode from standby mode. This command has no
effect if the device is already in conversion mode.
8.5.3.5 LOCK (0000 0101 0101 0101)
The LOCK command locks the interface, preventing the device from accidentally latching unwanted commands
that can change the state of the device. When the interface is locked, the device only responds to the NULL,
RREG, and UNLOCK commands. The device continues to output conversion data even when locked.
8.5.3.6 UNLOCK (0000 0110 0110 0110)
The UNLOCK command unlocks the interface if previously locked by the LOCK command.
8.5.3.7 RREG (101a aaaa annn nnnn)
The RREG is used to read the device registers. The binary format of the command word is 101a aaaa annn
nnnn, where a aaaa a is the binary address of the register to begin reading and nnn nnnn is the unsigned
binary number of consecutive registers to read minus one. There are two cases for reading registers on the
ADS131B02-Q1. When reading a single register (nnn nnnn = 000 0000b), the device outputs the register
contents in the command response word of the following frame. If multiple registers are read using a single
command (nnn nnnn > 000 0000b), the device outputs the requested register data sequentially in order of
addresses.
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8.5.3.7.1 Reading a Single Register
Read a single register from the device by specifying nnn nnnn as zero in the RREG command word. As with all
SPI commands on the ADS131B02-Q1, the response occurs on the output in the frame following the command.
Instead of a unique acknowledgment word, the response word is the contents of the register whose address is
specified in the command word. Figure 8-21 shows an example of reading a single register.
DRDY
CS
SCLK
DIN
DOUT
Hi-Z
RREG
CRC
Response
Channel 0 Data
Channel 1 Data
CRC
Command
CRC
Register
Data
Channel 0 Data
Hi-Z
Figure 8-21. Reading a Single Register
8.5.3.7.2 Reading Multiple Registers
Multiple registers are read from the device when nnn nnnn is specified as a number greater than zero in the
RREG command word. Like all SPI commands on the ADS131B02-Q1, the response occurs on the output
in the frame following the command. Instead of a single acknowledgment word, the response spans multiple
words in order to shift out all requested registers. Continue toggling SCLK to accommodate outputting the entire
data stream. ADC conversion data are not output in the frame following an RREG command to read multiple
registers. Figure 8-22 shows an example of reading multiple registers.
CS
SCLK
DIN
DOUT
Hi-Z
RREG
CRC
Response
Channel 0 Data
Channel 1 Data
CRC
Hi-Z
Command
CRC
RREG
ack
1st UHJLVWHU¶V
data
2nd UHJLVWHU¶V
data
N-1th UHJLVWHU¶V
data
Nth UHJLVWHU¶V
data
CRC
Hi-Z
Figure 8-22. Reading Multiple Registers
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8.5.3.8 WREG (011a aaaa annn nnnn)
The WREG command allows writing an arbitrary number of contiguous device registers. The binary format of the
command word is 011a aaaa annn nnnn, where a aaaa a is the binary address of the register to begin writing
and nnn nnnn is the unsigned binary number of consecutive registers to write minus one. Send the data to be
written immediately following the command word. Write the intended contents of each register into individual
words, MSB aligned.
If the input CRC is enabled, write this CRC after the register data. The registers are written to the device as
they are shifted into DIN. Therefore, a CRC error does not prevent an erroneous value from being written to a
register. An input CRC error during a WREG command sets the CRC_ERR bit in the STATUS register.
The device ignores writes to read-only registers or to out-of-bounds addresses. Gaps in the register map
address space are still included in the parameter nnn nnnn, but are not writeable so no change is made to them.
The response to the WREG command that occurs in the following frame appears as 010a aaaa ammm mmmm
where mmm mmmm is the number of registers actually written minus one. This number can be checked by the
host against nnn nnnn to make sure the expected number of registers are written.
Figure 8-23 shows a typical WREG sequence. In this example, the number of registers to write is larger than
the number of ADC channels and, therefore, the frame is extended beyond the ADC channels and output CRC
word. Make sure all of the ADC data and output CRC are shifted out during each transaction where new data are
available. Therefore, the frame must be extended beyond the number of words required to send the register data
in some cases.
DRDY
CS
SCLK
DIN
DOUT
Hi-Z
WREG
1st UHJLVWHU¶V
data
2nd UHJLVWHU¶V
data
3rd UHJLVWHU¶V
data
Response
Channel 0 Data
Channel 1 Data
CRC
4th UHJLVWHU¶V
data
5th UHJLVWHU¶V
data
6th UHJLVWHU¶V
data
N-1th UHJLVWHU¶V
data
Nth UHJLVWHU¶V
data
'RQ¶W &DUH
CRC
Hi-Z
Command
CRC
Response
Channel 0 Data
Figure 8-23. Writing Registers
8.5.4 Collecting Data for the First Time or After a Pause in Data Collection
Take special precaution when collecting data for the first time or when beginning to collect data again after a
pause. The internal mechanism that outputs data contains a first-in-first-out (FIFO) buffer that can store two
samples of data per channel at a time. The DRDY flag for each channel in the STATUS register remains set
until both samples for each channel are read from the device. This condition is not obvious under normal
circumstances when the host is reading each consecutive sample from the device. In that case, the samples are
cleared from the device each time new data are generated so the DRDY flag for each channel in the STATUS
register is cleared with each read. However, both slots of the FIFO are full if a sample is missed or if data are
not read for a period of time. Either strobe the SYNC/RESET pin to resynchronize conversions and clear the
FIFOs, or quickly read two data packets when data are read for the first time or after a gap in reading data.
This process maintains predictable DRDY pin behavior. See the Synchronization section for information about
the synchronization feature. These methods do not need to be employed if each channel data was read for each
output data period from when the ADC was enabled.
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Figure 8-24 shows an example of how to collect data after a period of the ADC running, but where no data
are being retrieved. In this instance, the SYNC/RESET pin is used to clear the internal FIFOs and realign the
ADS131B02-Q1 output data with the host.
Time where data is
not being read
DRDY
SYNC / RESET
SYNC Pulse
CS
SCLK
DOUT
Data
Data
Hi-Z
CRC
Status
Data
CRC
Figure 8-24. Collecting Data After a Pause in Data Collection Using the SYNC/RESET Pin
Another functionally equivalent method for clearing the FIFO after a pause in collecting data is to begin by
reading two samples in quick succession. Figure 8-25 depicts this method. There is a very narrow pulse on
DRDY immediately after the first set of data are shifted out of the device. This pulse may be too narrow for some
microcontrollers to detect. Therefore, do not rely upon this pulse, but instead immediately read out the second
data set after the first data set. DRDY transitions high after the second data set is read, which indicates that no
other new data are available for readout.
Time where data is
not being read
Narrow DRDY Pulse
DRDY
CS
SCLK
DOUT
Data
Data
CRC
Hi-Z
Status
Data
CRC
Status
Data
CRC
Data is read a
second time
Figure 8-25. Collecting Data After a Pause in Data Collection by Reading Data Twice
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8.6 Register Map
Table 8-11 lists the ADS131B02-Q1 registers. All register addresses not listed in Table 8-11 should be
considered as reserved locations and the register contents should not be modified.
Table 8-11. Register Map
ADDRESS
REGISTER
RESET
VALUE
BIT 15
BIT 14
BIT 13
BIT 12
BIT 11
BIT 10
BIT 9
BIT 8
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
DEVICE SETTINGS AND STATUS INDICATORS (Read-Only Registers)
00h
ID
42xxh
01h
STATUS
0500h
RESERVED
CHANCNT[3:0]
RESERVED
LOCK
F_RESYNC
REG_MAP
CRC_ERR
CRC_TYPE
RESET
RESERVED
WLENGTH[1:0]
DRDY1
DRDY0
GLOBAL SETTINGS ACROSS CHANNELS
02h
MODE
RESERVED
0510h
03h
CLOCK
038Eh
04h
GAIN
0000h
05h
RESERVED
06h
GLOBAL_CHOP_
CFG
0600h
07h
RESERVED
0000h
08h
RESERVED
0000h
REGCRC_EN
RESERVED
RX_CRC_EN
CRC_TYPE
TIMEOUT
RESET
RESERVED
RESERVED
CLK_SEL
RESERVED
OSR[2:0]
WLENGTH[1:0]
DRDY_HiZ
RESERVED
CH1_EN
CH0_EN
PWR[1:0]
RESERVED
RESERVED
PGAGAIN1[2:0]
RESERVED
PGAGAIN0[2:0]
RESERVED
0000h
RESERVED
RESERVED
GC_DLY[3:0]
GC_EN
RESERVED
RESERVED
RESERVED
RESERVED
RESERVED
CHANNEL-SPECIFIC SETTINGS
09h
CH0_CFG
0000h
0Ah
CH0_OCAL_MSB
0000h
0Bh
CH0_OCAL_LSB
0000h
0Ch
CH0_GCAL_MSB
8000h
0Dh
CH0_GCAL_LSB
0000h
0Eh
CH1_CFG
0000h
0Fh
CH1_OCAL_MSB
0000h
10h
CH1_OCAL_LSB
0000h
11h
CH1_GCAL_MSB
8000h
12h
CH1_GCAL_LSB
0000h
RESERVED
RESERVED
MUX0[1:0]
OCAL0_MSB[15:8]
OCAL0_MSB[7:0]
OCAL0_LSB[7:0]
RESERVED
GCAL0_MSB[15:8]
GCAL0_MSB[7:0]
GCAL0_LSB[7:0]
RESERVED
RESERVED
RESERVED
MUX1[1:0]
OCAL1_MSB[15:8]
OCAL1_MSB[7:0]
OCAL1_LSB[7:0]
RESERVED
GCAL1_MSB[15:8]
GCAL1_MSB[7:0]
GCAL1_LSB[7:0]
RESERVED
REGISTER MAP CRC AND RESERVED REGISTERS
3Eh
REGMAP_CRC
0000h
3Fh
RESERVED
0000h
REG_CRC[15:8]
REG_CRC[7:0]
RESERVED
RESERVED
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Table 8-12 shows the codes that are used for access types in this section.
Table 8-12. Access Type Codes
Access Type
Code
Description
R
Read
W
Write
Read Type
R
Write Type
W
Reset or Default Value
-n
Value after reset or the default value
8.6.1 ID Register (Address = 00h) [reset = 42xxh]
The ID register is shown in Figure 8-26 and described in Table 8-13.
Return to the Summary Table.
Figure 8-26. ID Register
15
14
7
13
12
11
10
RESERVED
CHANCNT[3:0]
R-0100b
R-0010b
6
5
4
3
2
9
8
1
0
RESERVED
R-xxxxxxxxb
Table 8-13. ID Register Field Descriptions
Bit
Field
Type
Reset
Description
RESERVED
R
0100b
Reserved
Always reads 0100b
11:8
CHANCNT[3:0]
R
0010b
Channel count
Always reads 0010b
7:0
RESERVED
R
xxxxxxxxb
Reserved
Values are subject to change without notice
15:12
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8.6.2 STATUS Register (Address = 01h) [reset = 0500h]
The STATUS register is shown in Figure 8-27 and described in Table 8-14.
Return to the Summary Table.
Figure 8-27. STATUS Register
15
14
13
12
11
10
9
8
LOCK
F_RESYNC
REG_MAP
CRC_ERR
CRC_TYPE
RESET
WLENGTH[1:0]
R-0b
R-0b
R-0b
R-0b
R-0b
R-1b
R-01b
7
6
5
4
3
2
1
0
RESERVED
DRDY1
DRDY0
R-000000b
R-0b
R-0b
Table 8-14. STATUS Register Field Descriptions
Bit
Field
Type
Reset
Description
15
LOCK
R
0b
SPI interface lock indicator
0b = Unlocked
1b = Locked
14
F_RESYNC
R
0b
ADC resynchronization indicator
Bit is set each time the ADC resynchronizes.
0b = No resynchronization
1b = Resynchronization occurred
13
REG_MAP
R
0b
Register map CRC fault indicator
0b = No change in the register map CRC
1b = register map CRC changed
12
CRC_ERR
R
0b
SPI input CRC error indicator
0b = No CRC error
1b = Input CRC error occured
11
CRC_TYPE
R
0b
CRC type indicator
0b = 16 bit CCITT
1b = 16 bit ANSI
10
RESET
R
1b
Reset status indicator
0b = No reset occurred
1b = Reset occurred
9:8
WLENGTH[1:0]
R
01b
Data word length indicator
00b = 16 bit
01b = 24 bits
10b = 32 bits: LSB zero padding
11b = 32 bits: MSB sign extension
7:2
RESERVED
R
000000b
Reserved
Always reads 000000b
1
DRDY1
R
0b
Channel 1 ADC data available indicator
0b = No new data available
1b = New data available
0
DRDY0
R
0b
Channel 0 ADC data available indicator
0b = No new data available
1b = New data available
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8.6.3 MODE Register (Address = 02h) [reset = 0510h]
The MODE register is shown in Figure 8-28 and described in Table 8-15.
Return to the Summary Table.
Figure 8-28. MODE Register
15
14
13
12
11
RESERVED
REG_CRC_EN
RX_CRC_EN
CRC_TYPE
RESET
WLENGTH[1:0]
R/W-00b
R/W-0b
R/W-0b
R/W-0b
R/W-1b
R/W-01b
4
3
2
7
6
5
10
9
8
1
0
RESERVED
TIMEOUT
RESERVED
DRDY_HiZ
RESERVED
R/W-000b
R/W-1b
R/W-00b
R/W-0b
R/W-0b
Table 8-15. MODE Register Field Descriptions
Bit
Field
Type
Reset
Description
RESERVED
R/W
00b
Reserved
Always write 00b
13
REG_CRC_EN
R/W
0b
Register map CRC enable
0b = Disabled
1b = Enabled
12
RX_CRC_EN
R/W
0b
SPI input CRC enable
0b = Disabled
1b = Enabled
11
CRC_TYPE
R/W
0b
SPI and register map CRC type selection
0b = 16 bit CCITT
1b = 16 bit ANSI
10
RESET
R/W
1b
Reset
Write 0b to clear this bit in the STATUS register
0b = No reset occurred
1b = Reset occurred
9:8
WLENGTH[1:0]
R/W
01b
Data word length selection
00b = 16 bits
01b = 24 bits
10b = 32 bits: LSB zero padding
11b = 32 bits: MSB sign extension
7:5
RESERVED
R/W
000b
Reserved
Always write 000b
TIMEOUT
R/W
1b
SPI Timeout enable
0b = Disabled
1b = Enabled
3:2
RESERVED
R/W
00b
Reserved
Always write 00b
1
DRDY_HiZ
R/W
0b
DRDY pin state selection when conversion data is not available
0b = Logic high
1b = High impedance
0
RESERVED
R/W
0b
Reserved
Always write 0b
15:14
4
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8.6.4 CLOCK Register (Address = 03h) [reset = 038Eh]
The CLOCK register is shown in Figure 8-29 and described in Table 8-16.
Return to the Summary Table.
Figure 8-29. CLOCK Register
15
14
7
13
6
12
9
8
RESERVED
CH1_EN
CH0_EN
R-000000b
R/W-1b
R/W-1b
5
4
11
3
10
2
1
0
CLK_SEL
RESERVED
OSR[2:0]
PWR[1:0]
R/W-1b
R/W-00b
R/W-011b
R/W-10b
Table 8-16. CLOCK Register Field Descriptions
Bit
Field
Type
Reset
Description
RESERVED
R
000000b
Reserved
Always reads 000000b
9
CH1_EN
R/W
1b
Channel 1 ADC enable
0b = Disabled
1b = Enabled
8
CH0_EN
R/W
1b
Channel 0 ADC enable
0b = Disabled
1b = Enabled
7
CLK_SEL
R/W
1b
Clock source selection
0b = Internal oscillator
1b = External clock
6:5
RESERVED
R/W
00b
Reserved
Always write 00b
4:2
OSR[2:0]
R/W
011b
Modulator oversampling ratio selection
000b = 128
001b = 256
010b = 512
011b = 1024
100b = 2048
101b = 4096
110b = 8192
111b = 16384
1:0
PWR[1:0]
R/W
10b
Power mode selection
00b = Very-low power
01b = Low power
10b = High resolution
11b = High resolution
15:10
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8.6.5 GAIN Register (Address = 04h) [reset = 0000h]
The GAIN register is shown in Figure 8-30 and described in Table 8-17.
Return to the Summary Table.
Figure 8-30. GAIN Register
15
14
13
12
11
10
9
8
1
0
RESERVED
R/W-00000000b
7
6
5
4
3
2
RESERVED
PGAGAIN1[2:0]
RESERVED
PGAGAIN0[2:0]
R/W-0b
R/W-000b
R/W-0b
R/W-000b
Table 8-17. GAIN Register Field Descriptions
Field
Type
Reset
Description
15:7
Bit
RESERVED
R/W
00000000
0b
Reserved
Always write 000000000b
6:4
PGAGAIN1[2:0]
R/W
000b
PGA gain selection for channel 1
000b = 1
001b = 2
010b = 4
011b = 8
100b = 16
101b = 32
110b = 64
111b = 128
RESERVED
R/W
0b
Reserved
Always write 0b
PGAGAIN0[2:0]
R/W
000b
PGA gain selection for channel 0
000b = 1
001b = 2
010b = 4
011b = 8
100b = 16
101b = 32
110b = 64
111b = 128
3
2:0
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8.6.6 RESERVED Register (Address = 05h) [reset = 0000h]
The RESERVED register is shown in Figure 8-33 and described in Table 8-20.
Return to the Summary Table.
Figure 8-31. RESERVED Register
15
14
13
12
11
10
9
8
2
1
0
RESERVED
R/W-00000000b
7
6
5
4
3
RESERVED
R/W-00000000b
Table 8-18. RESERVED Register Field Descriptions
Bit
15:0
Field
Type
Reset
Description
RESERVED
R/W
00000000
00000000b
Reserved
Always write 0000000000000000b
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8.6.7 GLOBAL_CHOP_CFG Register (Address = 06h) [reset = 0600h]
The GLOBAL_CHOP_CFG register is shown in Figure 8-32 and described in Table 8-19.
Return to the Summary Table.
Figure 8-32. GLOBAL_CHOP_CFG Register
15
14
13
12
11
10
9
8
RESERVED
GC_DLY[3:0]
GC_EN
R/W-000b
R/W-0011b
R/W-0b
7
6
5
4
3
2
1
0
RESERVED
R/W-00000000b
Table 8-19. GLOBAL_CHOP_CFG Register Field Descriptions
Field
Type
Reset
Description
15:13
Bit
RESERVED
R/W
000b
Reserved
Always write 000b
12:9
GC_DLY[3:0]
R/W
0011b
Global chop delay selection
Delay in modulator clock periods (tMOD) before measurement begins.
0000b = 2
0001b = 4
0010b = 8
0011b = 16
0100b = 32
0101b = 64
0110b = 128
0111b = 256
1000b = 512
1001b = 1024
1010b = 2048
1011b = 4096
1100b = 8192
1101b = 16484
1110b = 32768
1111b = 65536
GC_EN
R/W
0b
Global chop enable
0b = Disabled
1b = Enabled
RESERVED
R/W
00000000b
Reserved
Always write 00000000b
8
7:0
44
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8.6.8 RESERVED Register (Address = 07h) [reset = 0000h]
The RESERVED register is shown in Figure 8-33 and described in Table 8-20.
Return to the Summary Table.
Figure 8-33. RESERVED Register
15
14
13
12
11
10
9
8
2
1
0
9
8
1
0
RESERVED
R/W-00000000b
7
6
5
4
3
RESERVED
R/W-00000000b
Table 8-20. RESERVED Register Field Descriptions
Bit
15:0
Field
Type
Reset
Description
RESERVED
R/W
00000000
00000000b
Reserved
Always write 0000000000000000b
8.6.9 RESERVED Register (Address = 08h) [reset = 0000h]
The RESERVED register is shown in Figure 8-34 and described in Table 8-21.
Return to the Summary Table.
Figure 8-34. RESERVED Register
15
14
13
12
11
10
RESERVED
R/W-00000000b
7
6
5
4
3
2
RESERVED
RESERVED
R-0000b
R/W-0000b
Table 8-21. RESERVED Register Field Descriptions
Bit
Field
Type
Reset
Description
15:8
RESERVED
R/W
00000000b
Reserved
Always write 00000000b
7:4
RESERVED
R
0000b
Reserved
Always reads 0000b
3:0
RESERVED
R/W
0000b
Reserved
Always write 0000b
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8.6.10 CH0_CFG Register (Address = 09h) [reset = 0000h]
The CH0_CFG register is shown in Figure 8-35 and described in Table 8-22.
Return to the Summary Table.
Figure 8-35. CH0_CFG Register
15
14
13
12
11
10
9
2
1
8
RESERVED
R/W-00000000b
7
6
5
4
3
0
RESERVED
RESERVED
RESERVED
MUX0[1:0]
R/W-00b
R-000b
R/W-0b
R/W-00b
Table 8-22. CH0_CFG Register Field Descriptions
Field
Type
Reset
Description
15:6
Bit
RESERVED
R/W
00000000
00b
Reserved
Always write 0000000000b
5:3
RESERVED
R
000b
Reserved
Always reads 000b
2
RESERVED
R/W
0b
Reserved
Always write 0b
MUX0[1:0]
R/W
00b
Channel 0 input selection
00b = AIN0P and AIN0N
01b = AIN0 disconnected, ADC inputs shorted
10b = Positive dc test signal
11b = Negative dc test signal
1:0
46
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8.6.11 CH0_OCAL_MSB Register (Address = 0Ah) [reset = 0000h]
The CH0_OCAL_MSB register is shown in Figure 8-36 and described in Table 8-23.
Return to the Summary Table.
Figure 8-36. CH0_OCAL_MSB Register
15
14
13
12
11
10
9
8
2
1
0
OCAL0_MSB[15:8]
R/W-00000000b
7
6
5
4
3
OCAL0_MSB[7:0]
R/W-00000000b
Table 8-23. CH0_OCAL_MSB Register Field Descriptions
Bit
15:0
Field
Type
Reset
Description
OCAL0_MSB[15:0]
R/W
00000000
00000000b
Channel 0 offset calibration register bits [23:8]
Value provided in two's complement format
8.6.12 CH0_OCAL_LSB Register (Address = 0Bh) [reset = 0000h]
The CH0_OCAL_LSB register is shown in Figure 8-37 and described in Table 8-24.
Return to the Summary Table.
Figure 8-37. CH0_OCAL_LSB Register
15
14
13
12
11
10
9
8
2
1
0
OCAL0_LSB[7:0]
R/W-00000000b
7
6
5
4
3
RESERVED
R-00000000b
Table 8-24. CH0_OCAL_LSB Register Field Descriptions
Bit
Field
Type
Reset
Description
15:8
OCAL0_LSB[7:0]
R/W
00000000b
Channel 0 offset calibration register bits [7:0]
Value provided in two's complement format
7:0
RESERVED
R
00000000b
Reserved
Always reads 00000000b
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8.6.13 CH0_GCAL_MSB Register (Address = 0Ch) [reset = 8000h]
The CH0_GCAL_MSB register is shown in Figure 8-38 and described in Table 8-25.
Return to the Summary Table.
Figure 8-38. CH0_GCAL_MSB Register
15
14
13
12
11
10
9
8
2
1
0
GCAL0_MSB[15:8]
R/W-10000000b
7
6
5
4
3
GCAL0_MSB[7:0]
R/W-00000000b
Table 8-25. CH0_GCAL_MSB Register Field Descriptions
Bit
15:0
Field
Type
Reset
Description
GCAL0_MSB[15:0]
R/W
10000000
00000000b
Channel 0 gain calibration register bits [23:8]
Unsigned number for the gain range from 0.0 to 2.0 x (224 – 1) / 224
8.6.14 CH0_GCAL_LSB Register (Address = 0Dh) [reset = 0000h]
The CH0_GCAL_LSB register is shown in Figure 8-39 and described in Table 8-26.
Return to the Summary Table.
Figure 8-39. CH0_GCAL_LSB Register
15
14
13
12
11
10
9
8
2
1
0
GCAL0_LSB[7:0]
R/W-00000000b
7
6
5
4
3
RESERVED
R-00000000b
Table 8-26. CH0_GCAL_LSB Register Field Descriptions
Bit
48
Field
Type
Reset
Description
15:8
GCAL0_LSB[7:0]
R/W
00000000b
Channel 0 gain calibration register bits [7:0]
Unsigned number for the gain range from 0.0 to 2.0 x (224 – 1) / 224
7:0
RESERVED
R
00000000b
Reserved
Always reads 00000000b
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8.6.15 CH1_CFG Register (Address = 0Eh) [reset = 0000h]
The CH1_CFG register is shown in Figure 8-40 and described in Table 8-27.
Return to the Summary Table.
Figure 8-40. CH1_CFG Register
15
14
13
12
11
10
9
2
1
8
RESERVED
R/W-00000000b
7
6
5
4
3
0
RESERVED
RESERVED
RESERVED
MUX1[1:0]
R/W-00b
R-000b
R/W-0b
R/W-00b
Table 8-27. CH1_CFG Register Field Descriptions
Field
Type
Reset
Description
15:6
Bit
RESERVED
R/W
00000000
00b
Reserved
Always write 0000000000b
5:3
RESERVED
R
000b
Reserved
Always reads 000b
2
RESERVED
R/W
0b
Reserved
Always write 0b
MUX1[1:0]
R/W
00b
Channel 1 input selection
00b = AIN1P and AIN1N
01b = AIN1 disconnected, ADC inputs shorted
10b = Positive dc test signal
11b = Negative dc test signal
1:0
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8.6.16 CH1_OCAL_MSB Register (Address = 0Fh) [reset = 0000h]
The CH1_OCAL_MSB register is shown in Figure 8-41 and described in Table 8-28.
Return to the Summary Table.
Figure 8-41. CH1_OCAL_MSB Register
15
14
13
12
11
10
9
8
2
1
0
OCAL1_MSB[15:8]
R/W-00000000b
7
6
5
4
3
OCAL1_MSB[7:0]
R/W-00000000b
Table 8-28. CH1_OCAL_MSB Register Field Descriptions
Bit
15:0
Field
Type
Reset
Description
OCAL1_MSB[15:0]
R/W
00000000
00000000b
Channel 1 offset calibration register bits [23:8]
Value provided in two's complement format
8.6.17 CH1_OCAL_LSB Register (Address = 10h) [reset = 0000h]
The CH1_OCAL_LSB register is shown in Figure 8-42 and described in Table 8-29.
Return to the Summary Table.
Figure 8-42. CH1_OCAL_LSB Register
15
14
13
12
11
10
9
8
2
1
0
OCAL1_LSB[7:0]
R/W-00000000b
7
6
5
4
3
RESERVED
R-00000000b
Table 8-29. CH1_OCAL_LSB Register Field Descriptions
Bit
50
Field
Type
Reset
Description
15:8
OCAL1_LSB[7:0]
R/W
00000000b
Channel 1 offset calibration register bits [7:0]
Value provided in two's complement format
7:0
RESERVED
R
00000000b
Reserved
Always reads 00000000b
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8.6.18 CH1_GCAL_MSB Register (Address = 11h) [reset = 8000h]
The CH1_GCAL_MSB register is shown in Figure 8-43 and described in Table 8-30.
Return to the Summary Table.
Figure 8-43. CH1_GCAL_MSB Register
15
14
13
12
11
10
9
8
2
1
0
GCAL1_MSB[15:8]
R/W-10000000b
7
6
5
4
3
GCAL1_MSB[7:0]
R/W-00000000b
Table 8-30. CH1_GCAL_MSB Register Field Descriptions
Bit
15:0
Field
Type
Reset
Description
GCAL1_MSB[15:0]
R/W
10000000
00000000b
Channel 1 gain calibration register bits [23:8]
Unsigned number for the gain range from 0.0 to 2.0 x (224 – 1) / 224
8.6.19 CH1_GCAL_LSB Register (Address = 12h) [reset = 0000h]
The CH1_GCAL_LSB register is shown in Figure 8-44 and described in Table 8-31.
Return to the Summary Table.
Figure 8-44. CH1_GCAL_LSB Register
15
14
13
12
11
10
9
8
2
1
0
GCAL1_LSB[7:0]
R/W-00000000b
7
6
5
4
3
RESERVED
R-00000000b
Table 8-31. CH1_GCAL_LSB Register Field Descriptions
Bit
Field
Type
Reset
Description
15:8
GCAL1_LSB[7:0]
R/W
00000000b
Channel 1 gain calibration register bits [7:0]
Unsigned number for the gain range from 0.0 to 2.0 x (224 – 1) / 224
7:0
RESERVED
R
00000000b
Reserved
Always reads 00000000b
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8.6.20 REGMAP_CRC Register (Address = 3Eh) [reset = 0000h]
The REGMAP_CRC register is shown in Figure 8-45 and described in Table 8-32.
Return to the Summary Table.
Figure 8-45. REGMAP_CRC Register
15
14
13
12
11
10
9
8
2
1
0
10
9
8
2
1
0
REG_CRC[15:8]
R-00000000b
7
6
5
4
3
REG_CRC[7:0]
R-00000000b
Table 8-32. REGMAP_CRC Register Field Descriptions
Bit
15:0
Field
Type
Reset
Description
REG_CRC[15:0]
R
00000000
00000000b
Register map CRC value
8.6.21 RESERVED Register (Address = 3Fh) [reset = 0000h]
The RESERVED register is shown in Figure 8-46 and described in Table 8-33.
Return to the Summary Table.
Figure 8-46. RESERVED Register
15
14
13
12
11
RESERVED
R/W-00000000b
7
6
5
4
3
RESERVED
R/W-00000000b
Table 8-33. RESERVED Register Field Descriptions
Bit
15:0
52
Field
Type
Reset
Description
RESERVED
R/W
00000000
00000000b
Reserved
Always write 0000000000000000b
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9 Application and Implementation
Note
Information in the following applications sections is not part of the TI component specification,
and TI does not warrant its accuracy or completeness. TI’s customers are responsible for
determining suitability of components for their purposes, as well as validating and testing their design
implementation to confirm system functionality.
9.1 Application Information
9.1.1 Troubleshooting
Table 9-1 lists common issues faced when designing with the ADS131B02-Q1 and the corresponding solutions.
This list is not comprehensive.
Table 9-1. Troubleshooting Common Issues Using the ADS131B02-Q1
ISSUE
POSSIBLE ROOT CAUSE
POSSIBLE SOLUTION
The F_RESYNC bit is set in the STATUS
word even though this bit was already
cleared.
The SYNC/RESET pin is being toggled
asynchronously to CLKIN.
The SYNC/RESET pin functions as a
constant synchronization check, rather than
a convert start pin. See the Synchronization
section for more details on the intended
usage of the SYNC/RESET pin.
The same ADC conversion data are output
twice before changing.
The entire frame is not being sent to the
device. The device does not recognize data
as being read.
Read all data words in the output data
frame, including those for channels that are
disabled.
9.1.2 Unused Inputs and Outputs
Leave any unused analog inputs floating or connect them to AGND.
Do not float unused digital inputs because excessive power-supply leakage current can result. Tie all unused
digital inputs to the appropriate levels, DVDD or DGND.
Tie the CLKIN pin to DGND if the internal oscillator is used.
Leave the DRDY pin unconnected if unused or connect it to DVDD using a weak pullup resistor.
9.1.3 Antialias Filter
An analog low-pass filter is required in front of each of the ADC channel inputs to prevent out-of-band noise
and interferers from coupling into the band of interest. Because the ADS131B02-Q1 is a delta-sigma ADC, the
integrated digital filter provides substantial attenuation for frequencies outside of the band of interest up to the
frequencies adjacent to fMOD. Therefore, a single-order RC filter with a cutoff frequency set at least two decades
below the modulator frequency provides sufficient antialiasing protection in the vast majority of applications.
Figure 9-1 shows a typical RC filter that yields a cutoff frequency of fC = 39.8 kHz, which is generally a good
starting point for a design that uses fMOD = 4.096 MHz.
Applications that only need to measure dc signals can use much lower filter-cutoff frequencies by increasing the
resistor or capacitor values. Larger resistor values have the added benefit of limiting the current into the ADC
inputs in case of an overvoltage event.
200
10 nF
To ADC
Inputs
200
Figure 9-1. Antialias Filter Example
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9.1.4 Minimum Interface Connections
Figure 9-2 depicts how the ADS131B02-Q1 can be configured for the minimum number of interface pins. This
configuration is useful when using data isolation to minimize the number of isolation channels required or when
the microcontroller (MCU) pins are limited.
The CLKIN pin requires an LVCMOS clock that can be either generated by the MCU or created using a local
LVCMOS output oscillator when the device is configured for use with an external clock. Otherwise tie the CLKIN
pin to DGND if the internal oscillator is used. Tie the SYNC/RESET pin to DVDD in hardware if unused. The
DRDY pin can be left floating if unused. Connect either SYNC/RESET or DRDY to the MCU to make sure the
MCU stays synchronized to ADC conversions. If the MCU provides CLKIN, the CLKIN periods can be counted
to determine the sample period rather than forcing synchronization using the SYNC/RESET pin or monitoring the
DRDY pin. Synchronization cannot be regained if a bit error occurs on the clock and samples can be missed if
the SYNC/RESET or DRDY pins are not used. CS can be tied low in hardware if the ADS131B02-Q1 is the only
device on the SPI bus. Make sure the data input and output CRC are enabled and are used to guard against
faulty register reads and writes if CS is tied low permanently.
Local
Oscillator
DVDD
OR
CLKIN
CLKOUT
SYNC/RESET
GPIO
OR
DRDY
Device
GPIO
CS
CS
MCU
OR
SCLK
SCLK
DIN
MOSI
DOUT
MISO
DGND
Figure 9-2. Minimum Connections Required to Operate the ADS131B02-Q1
54
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9.1.5 Multiple Device Configuration
Multiple ADS131B02-Q1 devices can be arranged to capture all signals simultaneously. The same clock must be
provided to all devices and the SYNC/RESET pins must be strobed simultaneously at least one time to align the
sample periods internally between devices.
The devices can share the same SPI bus where only the CS pins for each device are unique. Each device can
be addressed sequentially by asserting CS for the device that the host wishes to communicate with. The DOUT
pin remains high impedance when the CS pin is high, allowing the DOUT lines to be shared between devices
as long as no two devices sharing the bus simultaneously have their CS pins low. Figure 9-3 shows multiple
devices configured for simultaneous data acquisition while sharing the same SPI bus.
Monitoring the DRDY output of only one of the devices is sufficient because all devices convert simultaneously.
Device 1
SYNC/RESET
GPIO
CLKIN
CLKOUT
DRDY
IRQ
SCLK
SCLK
DIN
MOSI
DOUT
MISO
CS
MCU
CS1
CS2
...
CSn
Device 2
SYNC/RESET
CLKIN
DRDY
SCLK
DIN
DOUT
CS
Device n
SYNC/RESET
CLKIN
DRDY
SCLK
DIN
DOUT
CS
Figure 9-3. Multiple Device Configuration
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9.2 Typical Application
This section describes a typical battery management system (BMS) application circuit using the ADS131B02-Q1.
The device serves the following primary functions in this BMS:
•
•
•
Measure battery current with high resolution and accuracy using a low-side current shunt sensor
Measure peak currents and detect overcurrent or short-circuit conditions
Measure battery-pack voltage using a high-voltage resistor divider
Figure 9-4 shows the front-end for the battery management system circuit design.
PACK+
AVDD = 3.3 V
DVDD = 3.3 V
AVDD
DVDD
1 …F
1 …F
ADS131B02-Q1
RH1
RH2
Battery Pack
RH3
AIN0P
Battery Pack Voltage
Measurement
RL
AIN0N
CLKIN
DRDY
CS
SCLK
DIN
DOUT
SYNC/RESET
AIN1P
AIN1N
Current Shunt
Measurement
CAP
220 nF
PACK-
AGND
DGND
RSHUNT
Figure 9-4. ADS131B02-Q1 in a Typical Battery Management System Application
9.2.1 Design Requirements
Table 9-2. Design Requirements
DESIGN PARAMETER
VALUE
Current measurement
Current measurement range
±5 kA
Current shunt value
35 μΩ
Update rate
1 ms
Battery-pack voltage measurement
Voltage measurement range
56
0 V to 800 V
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9.2.2 Detailed Design Procedure
The following sections provide guidelines for selecting the external components and the configuration of the
ADS131B02-Q1 for the various measurements in this application example.
9.2.2.1 Current Shunt Measurement
In a typical BMS, the current through the shunt resistor must be measured in both directions for charging and
discharging the battery pack. In an overcurrent or short-circuit condition, the current can be as high as I BAT_MAX =
±5 kA in this example application. Therefore, the maximum voltage drop across the shunt is up to VSHUNT =
RSHUNT × IBAT_MAX = 35 μΩ × ±4 kA = ±140 mV.
In order to measure this shunt voltage, channel 1 of the ADS131B02-Q1 is configured for gain = 8, which allows
differential voltage measurements of VIN1 = VAIN1P – VAIN1N = ±VREF / 8 = ±1.2 V / 8 = ±150 mV. The integrated
charge pump in the device allows voltage measurements 300 mV below AGND for gains of 4 and higher while
using a unipolar analog power supply. This bipolar voltage measurement capability is important because one
side of the shunt is connected to the same GND potential as the AGND pin of the ADS131B02-Q1, which means
that the absolute voltage that the device must measure is up to 140 mV below AGND.
To enable fast overcurrent detection within 1 ms while providing high accuracy and resolution, the ADS131B02Q1 is operated at 4 kSPS (OSR = 1024, high-resolution mode) using global-chop mode. Global-chop mode
enables measurements with minimal offset error over temperature and time. The conversion time using these
settings is 0.754 ms according to Equation 6. The input-referred noise is approximately 1.29 μVRMS / √2 =
0.91 μVRMS following the explanations in the Noise Measurements section. Thus, currents as small as 0.91
μVRMS / 35 μΩ = 26 mA can be resolved. The resolution can be further improved by averaging the conversion
results over a longer period of time in the microcontroller that interfaces with the ADS131B02-Q1.
9.2.2.2 Battery Pack Voltage Measurement
The 800-V battery-pack voltage is divided down to the voltage range of the ADS131B02-Q1 using a high-voltage
resistor divider (RH1, RH2, RH3, and RL). Gain = 1 is used for channel 0 in this case to allow differential
voltage measurements of VIN0 = VAIN0P – VAIN0N = ±1.2 V. The battery-pack voltage measurement is a unipolar,
single-ended measurement. Thus, only the voltage range from 0 V to 1.2 V of the ADS131B02-Q1 is used.
Equation 9 calculates the resistor divider ratio.
VIN / VBAT_MAX = 1.2 V / 800 V = RL / (RL + RH1 + RH2 + RH3)
(9)
The leakage current drawn by the resistor divider should be less than 100 μA in this example to avoid
unnecessarily draining the battery. The resistance of the divider must therefore be larger than RTOTAL ≥
VBAT_MAX / ILEAKAGE = 800 V / 100 μA = 8 MΩ. The resistor values are chosen as RH1 = RH2 = RH3 = 2.8 MΩ and
RL = 12.4 kΩ. Thus, the maximum voltage across RL is 1.18 V at VBAT_MAX = 800 V, leaving some headroom to
the maximum input voltage of 1.2 V of the ADS131B02-Q1.
The maximum resistance of a single resistor that can be used in an automotive circuit design is often limited to
a certain value. Also, the maximum voltage a single resistor can withstand is limited. These reasons are why the
high-side resistor of the divider is split into multiple resistors (RH1, RH2, and RH3). Another reason is that in case
a single resistor has a short-circuit fault, the remaining resistors still limit the current into the ADS131B02-Q1
analog input pin (AIN0P) to safe levels.
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9.2.3 Application Curves
40
0.4
30
0.3
20
0.2
Gain Error (%)
Offset Current Error (mA)
Figure 9-5 shows the measurement accuracy of the current measurement (ADC channel 1) over temperature for
a 0-A current through the shunt. Figure 9-6 shows the gain error of the current measurement (ADC channel 1)
over temperature excluding the error of the shunt. The offset and gain error are calibrated at 25°C.
10
0
-10
0
-0.1
-20
-0.2
-30
-0.3
-40
-40
-20
0
20
40
60
80
Temperature (°C)
100
120
140
Figure 9-5. Offset Current Error vs Temperature
58
0.1
-0.4
-40
-20
0
20
40
60
80
Temperature (°C)
100
120
140
Figure 9-6. Gain Error vs Temperature
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10 Power Supply Recommendations
10.1 CAP Pin Capacitor Requirement
The ADS131B02-Q1 core digital supply voltage of 1.8 V is created by an internal LDO from DVDD. The CAP
pin outputs the LDO voltage created from the DVDD supply and requires an external bypass capacitor. Place a
220-nF capacitor on the CAP pin to DGND.
10.2 Power-Supply Sequencing
The power supplies can be sequenced in any order but the analog and digital inputs must never exceed the
respective analog or digital power-supply voltage limits.
10.3 Power-Supply Decoupling
Good power-supply decoupling is important to achieve optimum performance. AVDD and DVDD must each be
decoupled with a 1-µF capacitor. Place the bypass capacitors as close to the power-supply pins of the device
as possible with low-impedance connections. Using multi-layer ceramic chip capacitors (MLCCs) that offer low
equivalent series resistance (ESR) and inductance (ESL) characteristics are recommended for power-supply
decoupling purposes. For very sensitive systems, or for systems in harsh noise environments, avoiding the use
of vias for connecting the capacitors to the device pins can offer superior noise immunity. The use of multiple
vias in parallel lowers the overall inductance and is beneficial for connections to ground planes.
11 Layout
11.1 Layout Guidelines
For best performance, dedicate an entire PCB layer to a ground plane and do not route any other signal traces
on this layer. However, depending on restrictions imposed by specific end equipment, a dedicated ground plane
may not be practical. If ground plane separation is necessary, make a direct connection of the planes at the
ADC. Do not connect individual ground planes at multiple locations because this configuration creates ground
loops.
Route digital traces away from all analog inputs and associated components in order to minimize interference.
Use C0G capacitors on the analog inputs. Use ceramic capacitors (for example, X7R grade) for the powersupply decoupling capacitors. High-K capacitors (Y5V) are not recommended. Place the required capacitors as
close as possible to the device pins using short, direct traces. For optimum performance, use low-impedance
connections on the ground-side connections of the bypass capacitors.
When applying an external clock, be sure the clock is free of overshoot and glitches. A source-termination
resistor placed at the clock buffer often helps reduce overshoot. Glitches present on the clock input can lead to
noise within the conversion data.
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11.2 Layout Example
Figure 11-1 shows an example layout of the ADS131B02-Q1 requiring a minimum of two PCB layers. In general,
analog signals and planes are partitioned to the left and digital signals and planes to the right.
+3.3 V
Via to corresponding
voltage plane or pour
Via to ground plane
or pour
+3.3 V
+3.3 V
Place CAP and power supply
decoupling capacitors close to pins
1: AVDD
20: DVDD
2: AGND
19: DGND
3: AIN0P
18: CAP
4: AIN0N
17: CLKIN
Channel 0
5: AIN1N
16: DIN
Device
6: AIN1P
15: DOUT
7: NC
14: SCLK
8: NC
13: DRDY
9: NC
12: CS
10: NC
11: SYNC/RST
Channel 1
Differential RC-filter
per channel
Terminate long digital
input lines with resistors to
prevent reflection
Figure 11-1. Layout Example
60
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12 Device and Documentation Support
12.1 Receiving Notification of Documentation Updates
To receive notification of documentation updates, navigate to the device product folder on ti.com. In the upper
right corner, click on Alert me to register and receive a weekly digest of any product information that has
changed. For change details, review the revision history included in any revised document.
12.2 Support Resources
TI E2E™ support forums are an engineer's go-to source for fast, verified answers and design help — straight
from the experts. Search existing answers or ask your own question to get the quick design help you need.
Linked content is provided "AS IS" by the respective contributors. They do not constitute TI specifications and do
not necessarily reflect TI's views; see TI's Terms of Use.
12.3 Trademarks
TI E2E™ is a trademark of Texas Instruments.
All trademarks are the property of their respective owners.
12.4 Electrostatic Discharge Caution
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.
12.5 Glossary
TI Glossary
This glossary lists and explains terms, acronyms, and definitions.
13 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
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PACKAGE OPTION ADDENDUM
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8-Dec-2021
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
ADS131B02QPWRQ1
ACTIVE
TSSOP
PW
20
2000
RoHS & Green
NIPDAU
Level-3-260C-168 HR
-40 to 125
A131B02Q
(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)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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