TI1 ADS1191IPBS Low-power, 2-channel, 16-bit analog front-end for biopotential measurement Datasheet

ADS1191
ADS1192
www.ti.com
SBAS566A – DECEMBER 2011 – REVISED SEPTEMBER 2012
Low-Power, 2-Channel, 16-Bit Analog Front-End for Biopotential Measurements
Check for Samples: ADS1191, ADS1192
FEATURES
1
•
23
•
•
•
•
•
•
•
•
•
•
•
•
Two Low-Noise PGAs and
Two High-Resolution ADCs (ADS1192)
Low Power: 335 μW/channel
Input-Referred Noise: 24 μVPP
(150-Hz BW, G = 6)
Input Bias Current: 1 nA
Data Rate: 125 SPS to 8 kSPS
CMRR: –95 dB
Programmable Gain: 1, 2, 3, 4, 6, 8, or 12
Supplies: Unipolar or Bipolar
– Analog: 2.7 V to 5.25 V
– Digital: 1.7 V to 3.6 V
Built-In Right Leg Drive Amplifier, Lead-Off
Detection, Test Signals
Built-In Oscillator and Reference
Flexible Power-Down, Standby Mode
SPI™-Compatible Serial Interface
Operating Temperature Range: –40°C to +85°C
The ADS1191/2 incorporate all of the features that
are commonly required in portable, low-power
medical electrocardiogram (ECG), sports, and fitness
applications.
With its high levels of integration and exceptional
performance, the ADS1191/2 family enables the
creation of scalable medical instrumentation systems
at significantly reduced size, power, and overall cost.
The ADS1191/2 have a flexible input multiplexer per
channel that can be independently connected to the
internally-generated signals for test, temperature, and
lead-off detection. Additionally, any configuration of
input channels can be selected for derivation of the
right leg drive (RLD) output signal. The ADS1191/2
operate at data rates up to 8 kSPS. Lead-off
detection can be implemented internal to the device,
using the device internal excitation current
sink/source.
The devices are packaged in a 5-mm × 5-mm, 32-pin
thin quad flat pack (TQFP). Operating temperature is
specified from –40°C to +85°C.
REF
Test Signals and
Monitors
SPI
CLK
ADC1
A1
Oscillator
MUX
Control
A2
ADC2
To Channel
DESCRIPTION
The ADS1191/2 are a family of multichannel,
simultaneous sampling, 16-bit, delta-sigma (ΔΣ)
analog-to-digital converters (ADCs) with a built-in
programmable gain amplifier (PGA), internal
reference, and an onboard oscillator.
GPIO AND CONTROL
Medical Instrumentation (ECG) including:
– Patient monitoring; Holter, event, stress,
and vital signs including ECG, AED,
telemedicine
– Sports and fitness (heart rate, respiration,
and ECG)
INPUTS
•
Reference
SPI
APPLICATIONS
RLD
1
2
3
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
SPI is a trademark of Motorola.
All other trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2011–2012, Texas Instruments Incorporated
ADS1191
ADS1192
SBAS566A – DECEMBER 2011 – REVISED SEPTEMBER 2012
www.ti.com
This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more
susceptible to damage because very small parametric changes could cause the device not to meet its published specifications.
FAMILY AND ORDERING INFORMATION (1)
PRODUCT
PACKAGE
OPTION
PACKAGE
DESIGNATOR
NUMBER OF
CHANNELS
ADC
RESOLUTION
MAXIMUM
SAMPLE
RATE (kSPS)
OPERATING
TEMPERATU
RE RANGE
TQFP
PBS
1
16
8
–40°C to
+85°C
No
QFN
RSM
1
24
8
–40°C to
+85°C
No
TQFP
PBS
2
16
8
–40°C to
+85°C
No
QFN
RSM
2
24
8
–40°C to
+85°C
No
TQFP
PBS
1
24
8
–40°C to
+85°C
No
QFN
RSM
1
24
8
–40°C to
+85°C
No
TQFP
PBS
2
24
8
–40°C to
+85°C
No
QFN
RSM
2
24
8
–40°C to
+85°C
No
TQFP
PBS
2
24
8
–40°C to
+85°C
Yes
QFN
RSM
2
24
8
–40°C to
+85°C
Yes
ADS1191IPBS
ADS1192IPBS
ADS1291IPBS
ADS1292IPBS
ADS1292RIPBS
(1)
RESPIRATION
CIRCUITRY
For the most current package and ordering information, see the Package Option Addendum at the end of this document, or visit the
device product folder at www.ti.com.
ABSOLUTE MAXIMUM RATINGS (1)
Over operating free-air temperature range, unless otherwise noted.
VALUE
UNIT
AVDD to AVSS
–0.3 to +7
V
DVDD to DGND
–0.3 to +7
V
AVSS to DGND
–3 to +0.2
V
Analog input to AVSS
AVSS – 0.3 to AVDD + 0.3
V
Digital input to DVDD
DVSS – 0.3 to DVDD + 0.3
V
Input current to any pin except supply pins
(2)
±10
mA
Momentary
±100
mA
Continuous
±10
mA
Operating temperature range Industrial-grade devices only
–40 to +85
°C
Storage temperature range
–60 to +150
°C
+150
°C
Human body model (HBM)
JEDEC standard 22, test method A114-C.01, all pins
±1000
V
Charged device model (CDM)
JEDEC standard 22, test method C101, all pins
±500
V
Input current
Maximum junction temperature (TJ)
Electrostatic discharge
(ESD) ratings
(1)
(2)
2
Stresses above these ratings may cause permanent damage. Exposure to absolute maximum conditions for extended periods may
degrade device reliability. These are stress ratings only, and functional operation of the device at these or any other conditions beyond
those specified is not implied.
Input terminals are diode-clamped to the power-supply rails. Input signals that can swing beyond the supply rails must be current limited
to 10 mA or less.
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Copyright © 2011–2012, Texas Instruments Incorporated
Product Folder Links: ADS1191 ADS1192
ADS1191
ADS1192
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SBAS566A – DECEMBER 2011 – REVISED SEPTEMBER 2012
ELECTRICAL CHARACTERISTICS
Minimum and maximum specifications apply from –40°C to +85°C. Typical specifications are at +25°C. All specifications at
DVDD = 1.8 V, AVDD – AVSS = 3 V (1), VREF = 2.42 V, external fCLK = 512 kHz, data rate = 500 SPS, CFILTER = 4.7 nF (2), and
gain = 6, unless otherwise noted.
ADS1191, ADS1192
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
ANALOG INPUTS
Full-scale differential input voltage
(AINP – AINN)
±VREF/GAIN
See the Input Common-Mode Range
subsection of the PGA Settings and
Input Range section
Input common-mode range
Input capacitance
Input bias current
20
pF
Input = 1.5 V
±1
Input = 1.5 V, TA = –40°C to +85°C
No lead-off
DC input impedance
V
nA
±2
nA
1000
MΩ
Current source lead-off detection (nA range),
AVSS + 0.3 V < AIN < AVDD – 0.3 V
500
MΩ
Current source lead-off detection (µA range),
AVSS + 0.6 V < AIN < AVDD – 0.6 V
100
MΩ
PGA PERFORMANCE
Gain settings
BW
Bandwidth
1, 2, 3, 4, 6, 8, 12
With a 4.7-nF capacitor on PGA output
(see PGA Settings and Input Range section
for details)
8.5
kHz
ADC PERFORMANCE
DR
Resolution
16
Data rate
125
Bits
8000
SPS
CHANNEL PERFORMANCE (DC Performance)
Input-referred noise
Gain = 6 (3), 10 seconds of data
24.6
Gain = 6, 256 points, 0.5 seconds of data
24.6
Gain settings other than 6, data rate other
than 500 SPS
INL
Integral nonlinearity
μVPP
25
μVPP
See Noise Measurements section
Full-scale with gain = 6, best fit
±1
Input-referred offset error
LSB
μV
±100
Input-referred offset error drift
2
Offset error with calibration
μV/°C
μV
15
Gain error
Excluding voltage reference error
Gain drift
Excluding voltage reference drift
±0.5
Gain match between channels
% of FS
5
ppm/°C
1
% of FS
CHANNEL PERFORMANCE (AC performance)
CMRR
Common-mode rejection ratio
fCM = 50 Hz, 60 Hz (4)
PSRR
Power-supply rejection ratio
fPS = 50 Hz, 60 Hz
90
dB
Crosstalk
fIN = 50 Hz, 60 Hz
–120
dB
SNR
Signal-to-noise ratio
fIN = 10 Hz input, gain = 6
92
dB
THD
Total harmonic distortion
10 Hz, –0.5 dBFs
–100
dB
(1)
(2)
(3)
(4)
–95
dB
Performance is applicable for 5-V operation as well. Production testing for limits is performed at 3 V.
CFILTER is the capacitor accross the PGA outputs; see the PGA Settings and Input Range section for details.
Noise data measured in a 10-second interval. Test not performed in production. Input-referred noise is calculated with input shorted
(without electrode resistance) over a 10-second interval.
CMRR is measured with a common-mode signal of AVSS + 0.3 V to AVDD – 0.3 V. The values indicated are the minimum of the eight
channels.
Copyright © 2011–2012, Texas Instruments Incorporated
Product Folder Links: ADS1191 ADS1192
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ADS1191
ADS1192
SBAS566A – DECEMBER 2011 – REVISED SEPTEMBER 2012
www.ti.com
ELECTRICAL CHARACTERISTICS (continued)
Minimum and maximum specifications apply from –40°C to +85°C. Typical specifications are at +25°C. All specifications at
DVDD = 1.8 V, AVDD – AVSS = 3 V(1), VREF = 2.42 V, external fCLK = 512 kHz, data rate = 500 SPS, CFILTER = 4.7 nF(2), and
gain = 6, unless otherwise noted.
ADS1191, ADS1192
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
RIGHT LEG DRIVE (RLD) AMPLIFIER
μVRMS
Integrated noise
BW = 150 Hz
1.4
GBP
Gain bandwidth product
50 kΩ || 10 pF load, gain = 1
100
kHz
SR
Slew rate
50 kΩ || 10 pF load, gain = 1
0.07
V/μs
THD
Total harmonic distortion
fIN = 100 Hz, gain = 1
CMIR
Common-mode input range
Common-mode resistor matching
ISC
–85
AVSS + 0.3
Internal 200-kΩ resistor matching
Short-circuit current
Quiescent power consumption
dB
AVDD – 0.3
V
0.1
%
1.1
mA
5
μA
RLD amplifier
LEAD-OFF DETECT
Frequency
Current
See Register Map section for settings
0, fDR/4
kHz
ILEAD_OFF [1:0] = 00
6
ILEAD_OFF [1:0] = 01
22
nA
ILEAD_OFF [1:0] = 10
6
μA
22
μA
ILEAD_OFF [1:0] = 11
nA
Current accuracy
±20
%
Comparator threshold accuracy
±30
mV
EXTERNAL REFERENCE
Reference input voltage
VREFN
Negative input
VREFP
Positive input
AVDD = 3 V, VREF = (VREFP – VREFN)
2
AVDD = 5 V, VREF = (VREFP – VREFN)
2
2.5
VDD – 0.3
V
4
VDD – 0.3
V
AVSS
AVSS + 2.5
Input impedance
V
V
120
kΩ
CONFIG2.VREF_4V = 0
2.42
V
CONFIG2.VREF_4V = 1
4.033
V
100
µA
INTERNAL REFERENCE
Output voltage
Output current drive
Available for external use
VREF accuracy
±0.5
Internal reference drift
Start-up time
Settled to 0.2% with 10-µF capacitor on
VREFP pin
Quiescent current consumption
4
Submit Documentation Feedback
%
45
ppm/°C
100
ms
20
µA
Copyright © 2011–2012, Texas Instruments Incorporated
Product Folder Links: ADS1191 ADS1192
ADS1191
ADS1192
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SBAS566A – DECEMBER 2011 – REVISED SEPTEMBER 2012
ELECTRICAL CHARACTERISTICS (continued)
Minimum and maximum specifications apply from –40°C to +85°C. Typical specifications are at +25°C. All specifications at
DVDD = 1.8 V, AVDD – AVSS = 3 V(1), VREF = 2.42 V, external fCLK = 512 kHz, data rate = 500 SPS, CFILTER = 4.7 nF(2), and
gain = 6, unless otherwise noted.
ADS1191, ADS1192
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
SYSTEM MONITORS
Analog supply reading error
2
%
Digital supply reading error
2
%
From power supply ramp after power-on-reset
to DRDY low
32
ms
From power-down mode to DRDY low
10
ms
From STANDBY mode to DRDY low
10
ms
VCAP1 settling time
1% accuracy with 1-µF capacitor
0.5
s
Temperature sensor Voltage
reading
Coefficient
TA = +25°C
145
mV
490
μV/°C
Device wake up
TEST SIGNAL
Signal frequency
See Register Map section for settings
Signal voltage
See Register Map section for settings
At dc and 1 Hz
Accuracy
Hz
±1
mV
±2
%
CLOCK
Nominal frequency
Internal oscillator clock frequency
512
kHz
TA = +25°C
±0.5
–40°C ≤ TA ≤ +85°C
±1.5
%
%
Internal oscillator start-up time
32
μs
Internal oscillator power consumption
30
μW
External clock input frequency
CLKSEL pin = 0, CLK_DIV = 0
485
512
562.5
kHz
CLKSEL pin = 0, CLK_DIV = 1
1.94
2.048
2.25
MHz
DIGITAL INPUT/OUTPUT (DVDD = 1.8 V to 3.6 V)
Logic level
VIH (DVDD =
1.8 V to 3.6 V)
0.8 DVDD
DVDD + 0.1
V
VIL(DVDD =
1.8 V to 3.6 V)
–0.1
0.2 DVDD
V
VIH (DVDD =
1.7 V to 1.8 V)
DVDD – 0.2
V
VIL (DVDD =
1.7 V to 1.8 V)
Input current (IIN)
0 V < VDigitalInput < DVDD
–10
0.2
V
+10
μA
POWER-SUPPLY REQUIREMENTS (RLD Amplifiers Turned Off)
AVDD
Analog supply
DVDD
Digital supply
AVDD – AVSS
AVDD – DVDD
2.7
3
5.25
V
1.7
1.8
3.6
V
3.6
V
–2.1
SUPPLY CURRENT
IAVDD
IDVDD
ADS1192
ADS1192
AVDD – AVSS = 3 V
205
µA
AVDD – AVSS = 5 V
250
µA
DVDD = 3.3 V
75
µA
DVDD = 1.8 V
32
µA
Copyright © 2011–2012, Texas Instruments Incorporated
Product Folder Links: ADS1191 ADS1192
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ADS1191
ADS1192
SBAS566A – DECEMBER 2011 – REVISED SEPTEMBER 2012
www.ti.com
ELECTRICAL CHARACTERISTICS (continued)
Minimum and maximum specifications apply from –40°C to +85°C. Typical specifications are at +25°C. All specifications at
DVDD = 1.8 V, AVDD – AVSS = 3 V(1), VREF = 2.42 V, external fCLK = 512 kHz, data rate = 500 SPS, CFILTER = 4.7 nF(2), and
gain = 6, unless otherwise noted.
ADS1191, ADS1192
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
Normal mode
670
740
µW
Standby mode
160
Normal mode
450
Standby mode
160
µW
ADS1192
Normal mode
350
µW
ADS1191
Normal mode
400
µW
Normal mode
1300
µW
Standby mode
340
µW
Normal mode
950
µW
Standby mode
340
µW
ADS1192
Normal mode
670
µW
ADS1191
Normal mode
860
µW
DVDD = 1.8 V
1
µW
DVDD = 3.3 V
4
µW
DVDD = 1.8 V
5
µW
DVDD = 3.3 V
10
µW
POWER DISSIPATION (Analog Supply = 3 V, RLD Turned Off)
ADS1192
Quiescent power
dissipation
ADS1191
Quiescent power
dissipation, per
channel
µW
495
µW
POWER DISSIPATION (Analog Supply = 5 V, RLD Turned Off)
ADS1192
Quiescent power
dissipation
ADS1191
Quiescent power
dissipation, per
channel
POWER DISSIPATION IN POWER-DOWN MODE
Analog supply = 3 V
Analog supply = 5 V
TEMPERATURE
Specified temperature range
–40
+85
°C
Operating temperature range
Storage temperature range
–40
+85
°C
–60
+150
°C
THERMAL INFORMATION
ADS1191, ADS1192
THERMAL METRIC (1)
PBS (TQFP)
RSM (QFN)
32 PINS
32 PINS
θJA
Junction-to-ambient thermal resistance
68.4
33.7
θJCtop
Junction-to-case (top) thermal resistance
25.9
36.4
θJB
Junction-to-board thermal resistance
30.5
25.2
ψJT
Junction-to-top characterization parameter
0.5
0.2
ψJB
Junction-to-board characterization parameter
24.3
7.4
θJCbot
Junction-to-case (bottom) thermal resistance
N/A
2.2
(1)
6
UNITS
°C/W
For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953.
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Copyright © 2011–2012, Texas Instruments Incorporated
Product Folder Links: ADS1191 ADS1192
ADS1191
ADS1192
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SBAS566A – DECEMBER 2011 – REVISED SEPTEMBER 2012
PARAMETER MEASUREMENT INFORMATION
NOISE MEASUREMENTS
The ADS1191/2 noise performance can be optimized by adjusting the data rate and PGA setting. As the
averaging is increased by reducing the data rate, the noise drops correspondingly. Increasing the PGA value
reduces the input-referred noise, which is particularly useful when measuring low-level biopotential signals.
Table 1 and Table 2 summarize the noise performance of the ADS1191/2. The data are representative of typical
noise performance at TA = +25°C. The data shown are the result of averaging the readings from multiple devices
and are measured with the inputs shorted together.
Table 1 and Table 2 show measurements taken with an internal reference. The data are also representative of
the ADS1191/2 noise performance when using a low-noise external reference such as the REF5025.
Table 1. Input-Referred Noise (μVPP) 3-V Analog Supply and 2.42-V Reference (1)
PGA GAIN
DR BITS OF
CONFIG1
REGISTER
OUTPUT
DATA RATE
(SPS)
–3-dB BANDWIDTH
(Hz)
x1
x2
x3
x4
x6
x8
x12
μVPP
μVPP
μVPP
μVPP
μVPP
μVPP
μVPP
000
125
32.75
147.1
73.9
49.2
36.9
24.6
18.5
12.3
001
250
65.5
147.7
73.9
49.2
36.9
24.6
18.5
12.3
010
500
131
147.7
73.9
49.2
36.9
24.6
18.5
12.3
011
1000
262
147.7
73.9
49.2
36.9
24.6
18.5
12.3
100
2000
524
221.5
110.8
73.8
55.4
36.9
27.7
18.5
101
4000
1048
810.0
405.0
270.0
202.5
135.0
101.3
67.5
110
8000
2096
3900.0
1950.0
1300.0
975.0
650.0
487.5
325.0
(1)
At least 1000 consecutive readings were used to calculate the peak-to-peak noise values in this table.
Table 2. Input-Referred Noise (μVPP) 5-V Analog Supply and 4.033-V Reference (1)
PGA GAIN
DR BITS OF
CONFIG1
REGISTER
OUTPUT
DATA RATE
(SPS)
000
001
(1)
–3-dB BANDWIDTH
(Hz)
x1
x2
x3
x4
x6
x8
x12
μVPP
μVPP
μVPP
μVPP
μVPP
μVPP
μVPP
125
32.75
246.1
123.1
82.0
61.5
41.0
30.8
20.5
250
65.5
246.1
123.1
82.0
61.5
41.0
30.8
20.5
010
500
131
246.1
123.1
82.0
61.5
41.0
30.8
20.5
011
1000
262
246.1
123.1
82.0
61.5
41.0
30.8
20.5
100
2000
524
369.2
184.6
123.1
92.3
61.5
46.2
30.8
101
4000
1048
1230.0
615.0
410.0
307.5
205.0
153.8
102.5
110
8000
2096
6800.0
3400.0
2266.7
1700.0
1133.3
850.0
566.7
At least 1000 consecutive readings were used to calculate the peak-to-peak noise values in this table.
Copyright © 2011–2012, Texas Instruments Incorporated
Product Folder Links: ADS1191 ADS1192
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ADS1191
ADS1192
SBAS566A – DECEMBER 2011 – REVISED SEPTEMBER 2012
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TIMING CHARACTERISTICS
tCLK
CLK
tCSSC
tSCLK
SCLK
tCSH
tSDECODE
CS
1
tSPWL
tSPWH
3
2
8
1
tDIHD
tDIST
tSCCS
3
2
8
tDOPD
DIN
tCSDOZ
tCSDOD
Hi-Z
Hi-Z
DOUT
NOTE: SPI settings are CPOL = 0 and CPHA = 1.
Figure 1. Serial Interface Timing
Timing Requirements For Figure 1 (1)
2.7 V ≤ DVDD ≤ 3.6 V
PARAMETER
tCLK
DESCRIPTION
MAX
UNIT
TBD
TBD
TBD
TBD
ns
Master clock period (CLK_DIV bit of LOFF_STAT register = 1)
414
514
514
465
ns
CS low to first SCLK, setup time
tSCLK
tSPWH,
TYP
1.6 V ≤ DVDD ≤ 2.7 V
Master clock period (CLK_DIV bit of LOFF_STAT register = 0)
tCSSC
MIN
MAX
MIN
TYP
6
17
ns
SCLK period
50
66.6
ns
SCLK pulse width, high and low
15
25
ns
tDIST
DIN valid to SCLK falling edge: setup time
10
10
ns
tDIHD
Valid DIN after SCLK falling edge: hold time
10
11
tDOPD
SCLK rising edge to DOUT valid: setup time
tCSH
CS high pulse
tCSDOD
CS low to DOUT driven
tSCCS
L
12
ns
22
ns
2
2
10
20
ns
Eighth SCLK falling edge to CS high
4
4
tCLKs
tSDECODE
Command decode time
4
tCSDOZ
CS high to DOUT Hi-Z
(1)
8
tCLKs
4
10
tCLKs
20
ns
Specified at TA = –40°C to +85°C, unless otherwise noted. Load on DOUT = 20 pF || 100 kΩ.
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ADS1191
ADS1192
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SBAS566A – DECEMBER 2011 – REVISED SEPTEMBER 2012
PIN CONFIGURATIONS
6
19 DIN
PGA2N
7
18 CS
PGA2P
8
17 CLK
VREFP
IN3P
RLDOUT
RLDIN/RLDREF
RLDINV
VCAP2
GPIO1
GPIO2
25
PGA1N
1
24
DGND
PGA1P
2
23
DVDD
IN1N
3
22
DRDY
IN1P
4
21
DOUT
IN2N
5
20
SCLK
IN2P
6
19
DIN
PGA2N
7
18
CS
PGA2P
8
17
CLK
9
10
Copyright © 2011–2012, Texas Instruments Incorporated
Product Folder Links: ADS1191 ADS1192
11
12
13
14
15
16
START
IN2P
26
PWDN/RESET
20 SCLK
27
CLKSEL
5
28
AVSS
IN2N
29
AVDD
21 DOUT
30
VCAP1
4
31
VREFN
IN1P
32
VREFP
22 DRDY
START 16
3
PWDN/RESET 15
IN1N
CLKSEL 14
23 DVDD
AVSS 13
2
AVDD 12
PGA1P
VCAP1 11
24 DGND
VREFN 10
1
9
PGA1N
IN3N
25 GPIO2
RSM PACKAGE
QFN-32
(TOP VIEW)
26 GPIO1
27 VCAP2
28 RLDINV
29 RLDIN/RLDREF
30 RLDOUT
31 IN3P
32 IN3N
PBS PACKAGE
TQFP-32
(TOP VIEW)
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PIN ASSIGNMENTS
NAME
TERMINAL
FUNCTION
DESCRIPTION
AVDD
12
Supply
Analog supply
AVSS
13
Supply
Analog ground
CS
18
Digital input
Chip select
CLK
17
Digital input
Master clock input
CLKSEL
14
Digital input
Master clock select
DGND
24
Supply
DIN
19
Digital input
DOUT
21
Digital output
SPI data out
DRDY
22
Digital output
Data ready; active low
DVDD
23
Supply
GPIO1/RCLK1
26
Digital input/output
GPIO1
GPIO2/RCLK2
25
Digital input/output
GPIO2
IN1N (1)
3
Analog input
Differential analog negative input 1
(1)
4
Analog input
Differential analog positive input 1
IN2N (1)
5
Analog input
Differential analog negative input 2
IN2P (1)
6
Analog input
Differential analog positive input 2
PGA1N
1
Analog output
Differential analog negative output 1
IN1P
(1)
10
Digital ground
SPI data in
Digital power supply
PGA1P
2
Analog output
Differential analog positive output 1
PGA2N
7
Analog output
Differential analog negative output 2
PGA2P
8
Analog output
Differential analog positive output 2
PWDN/RESET
15
Digital input
Power-down/System reset; active low
RLDIN/RLDREF
29
Analog input
Right leg drive input to MUX/RLD reference
RLDINV
28
Analog input
Right leg drive inverting input
RLDOUT
30
Analog input
Right leg drive output
IN3N (1)
32
Analog input/output
Differential analog negative input 3
IN3P (1)
31
Analog input/output
Differential analog positive input 3
SCLK
20
Digital input
SPI clock
START
16
Digital input
Start conversion
VCAP1
11
—
Analog bypass capacitor
VCAP2
27
—
Analog bypass capacitor
VREFN
10
Analog input
Negative reference voltage
VREFP
9
Analog input/output
Positive reference voltage
Excludes effects of noise, linearity, offset, and gain error.
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TYPICAL CHARACTERISTICS
All plots at TA = +25°C, AVDD = 3 V, AVSS = 0 V, DVDD = 1.8 V, internal VREFP = 2.42 V, VREFN = AVSS,
external clock = 512 kHz, data rate = 500 SPS, and gain = 6, unless otherwise noted.
INTERNAL REFERENCE vs TEMPERATURE
CMRR vs FREQUENCY
−95
Common−Mode Rejection Ratio (dB)
Internal Reference (V)
2.424
2.422
2.42
2.418
2.416
−40
−15
10
35
Temperature (°C)
60
−105
−110
−115
Gain = 1
Gain = 2
Gain = 3
Gain = 4
Gain = 6
Gain = 8
Gain = 12
−120
−125
−130
−135
85
Data Rate = 8 kSPS
AIN = AVDD − 0.3 V to AVSS + 0.3 V
−100
10
100
Frequency (Hz)
G003
Figure 2.
1k
G004
Figure 3.
LEAKAGE CURRENT vs INPUT VOLTAGE
LEAKAGE CURRENT vs TEMPERATURE
0.2
1
Leakage Current (nA)
Leakage Current (nA)
0.8
0.1
0.6
0.4
0.2
0
0
0.5
1
1.5
2
Input Signal (V)
2.5
0
−40
3
−15
10
35
Temperature (°C)
G004
Figure 4.
85
G006
Figure 5.
PSRR vs FREQUENCY
THD vs FREQUENCY
120
110
Data Rate = 8 kSPS, −0.5 dBFS
Data Rate = 8 kSPS, −0.5 dBFS
110
100
100
THD (dB)
Power Supply Rejection Ratio (dB)
60
90
80
70
Gain = 1
Gain = 2
Gain = 3
Gain = 4
60
50
10
Gain = 6
Gain = 8
Gain = 12
90
Gain = 1
Gain = 2
Gain = 3
Gain = 4
Gain = 6
Gain = 8
Gain = 12
80
70
100
Frequency (Hz)
1k
60
10
G007
Figure 6.
100
Frequency (Hz)
1k
G006
Figure 7.
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TYPICAL CHARACTERISTICS (continued)
All plots at TA = +25°C, AVDD = 3 V, AVSS = 0 V, DVDD = 1.8 V, internal VREFP = 2.42 V, VREFN = AVSS,
external clock = 512 kHz, data rate = 500 SPS, and gain = 6, unless otherwise noted.
THD FFT PLOT
(60-Hz Signal)
FFT PLOT
(60-Hz Signal)
0
0
PGA Gain = 1
Input = 10Hz, −0.5 dBFS
THD = −96 dB
SNR = 92 dB
Data Rate =500 SPS
−40
−60
−80
−100
−40
−60
−80
−100
−120
−120
−140
−140
−160
0
50
100
150
Frequency (Hz)
200
PGA Gain = 1
Input = 10Hz, −0.5 dBFS
THD = −97 dB
SNR =76 dB
Data Rate = 8 kSPS
−20
Amplitude (dBFS)
Amplitude (dBFS)
−20
−160
250
0
1000
2000
Frequency (Hz)
G011
Figure 8.
3000
4000
G008
Figure 9.
TEST SIGNAL AMPLITUDE ACCURACY
LEAD-OFF COMPARATOR THRESHOLD ACCURACY
140
60
Data from 96 devices, Two lots
Data from 96 devices, Two Lots
Number of Bins
Number of Bins
120
40
20
100
80
60
40
20
12
10
8
6
4
2
0
−2
−4
−6
−8
−10
0.6
0.5
0.4
0.3
0.2
0.1
0
−0.1
−0.2
−0.3
−0.4
0
−0.5
0
Threshold Error (mV)
Error (%)
G014
G015
Figure 10.
Figure 11.
LEAD-OFF CURRENT SOURCE ACCURACY DISTRIBUTION
120
Data from 125 devices, Two lots
Current Setting = 24 nA
Number of Bins
100
80
60
40
20
2.5
2
1.5
1
0.5
0
−0.5
−1
−1.5
−2
0
Error in Current Magnitude (nA)
G016
Figure 12.
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OVERVIEW
The ADS1191/2 are low-power, multichannel, simultaneously-sampling, 16-bit delta-sigma (ΔΣ) analog-to-digital
converters (ADCs) with integrated programmable gain amplifiers (PGAs). These devices integrate various ECGspecific functions that make them well-suited for scalable electrocardiogram (ECG), sports, and fitness
applications. The devices can also be used in high-performance, multichannel data acquisition systems by
powering down the ECG-specific circuitry.
The ADS1191/2 have a highly programmable multiplexer that allows for temperature, supply, input short, and
RLD measurements. Additionally, the multiplexer allows any of the input electrodes to be programmed as the
patient reference drive. The PGA gain can be chosen from one of seven settings (1, 2, 3, 4, 6, 8, and 12). The
ADCs in the device offer data rates from 125 SPS to 8 kSPS. Communication to the device is accomplished
using an SPI-compatible interface. The device provides two general-purpose I/O (GPIO) pins for general use.
Multiple devices can be synchronized using the START pin.
The internal reference can be programmed to either 2.42 V or 4.033 V. The internal oscillator generates a 512kHz clock. The versatile right leg drive (RLD) block allows the user to choose the average of any combination of
electrodes to generate the patient drive signal. Lead-off detection can be accomplished either by using an
external pull-up/pull-down resistor or the device internal current source/sink. An internal ac lead-off detection
feature is also available. A detailed diagram of the ADS1191/2 is shown in Figure 13.
AVDD
VCAP1
PGA1P
PGA1N
Power-Supply Signal
VREFP VCAP2 VREFN
DVDD
Reference
Temperature Sensor Input
Test Signal
DRDY
Lead-Off Excitation Source
SPI
IN1P
EMI
Filter
CLKSEL
PGA1
ADC1
IN1N
Oscillator
Control
IN2P
EMI
Filter
CS
SCLK
DIN
DOUT
CLK
GPIO1/
RCLK
MUX
IN2N
GPIO2/
RCLK
RESP
PG A2
ADC2
PWDN/
RESET
V
START
(AVDD + AVSS)/2
RLD
Amplifier
AVSS
RLDIN/
RLDREF
RLD
OUT
RLD
INV
PGA2N
PGA2P
DGND
Figure 13. Functional Block Diagram
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THEORY OF OPERATION
This section contains details of the ADS1191/2 internal functional elements. The analog blocks are discussed
first followed by the digital interface. Blocks implementing ECG-specific functions are covered in the end.
Throughout this document, fCLK denotes the frequency of the signal at the CLK pin, tCLK denotes the period of the
signal at the CLK pin, fDR denotes the output data rate, tDR denotes the time period of the output data, and fMOD
denotes the frequency at which the modulator samples the input.
EMI FILTER
An RC filter at the input acts as an EMI filter on channels 1 and 2. The –3-dB filter bandwidth is approximately
3 MHz.
INPUT MULTIPLEXER
The ADS1191/2 input multiplexers are very flexible and provide many configurable signal switching options.
Refer to Figure 14 for a diagram of the ADS1191/2 multiplexer. Note that IN3P, IN3N, and RLDIN are common to
both channels. VINP and VINN are separate for each of the three pins. This flexibility allows for significant device
and sub-system diagnostics, calibration, and configuration. Selection of switch settings for each channel is made
by writing the appropriate values to the CH1SET or CH2SET register (see the CH1SET and CH2SET Registers
in the Register Map section for details.) More details of the ECG-specific features of the multiplexer are
discussed in the Input Multiplexer subsection of the ECG-Specifc Functions.
Device Noise Measurements
Setting CHnSET[3:0] = 0001 sets the common-mode voltage of (VREFP + VREFN)/2 to both inputs of the
channel. This setting can be used to test the inherent noise of the device in the user system.
Test Signals (TestP and TestN)
Setting CHnSET[2:0] = 101 provides internally-generated test signals for use in sub-system verification at powerup. This functionality allows the entire signal chain to be tested out. Although the test signals are similar to the
CAL signals described in the IEC60601-2-51 specification, this feature is not intended for use in compliance
testing.
Control of the test signals is accomplished through register settings (see the CONFIG2: Configuration Register 2
subsection in the Register Map section for details). TEST_AMP controls the signal amplitude and TEST_FREQ
controls switching at the required frequency.
14
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INT_TEST
Device
MUX1[3:0] = 0101
TESTP
MUX1[3:0] = 0100
TEMPP
MUX1[3:0] = 0011
MVDDP
From LOFFP
MUX1[3:0] = 0000
IN2P
To PGA2_INP
MUX1[3:0] = 0110 or
MUX1[3:0] = 1000
MUX1[3:0] = 0001
MUX1[3:0] = 0010
EMI
Filter
VREFP + VREFN
2
MUX1[3:0] = 0111 or
MUX1[3:0] = 1000
MUX1[3:0] = 0001
MUX1[3:0] = 0000
IN2N
From LOFFN
MUX1[3:0] = 0010
RLD_REF
MUX1[3:0] = 1001
MUX1[3:0] = 0011
MVDDN
MUX1[3:0] = 0100
TEMPN
INT_TEST
TESTM
RLDIN/
RLDREF
To PGA2_INN
MUX1[3:0] = 1001
MUX1[3:0] = 0101
INT_TEST
MUX1[3:0] = 0101
TESTP
MUX1[3:0] = 0100
TEMPP
MUX1[3:0] = 0011
MVDDP
From LOFFP
MUX1[3:0] = 0000
IN1P
To PGA1_INP
MUX1[3:0] = 0111 or
MUX1[3:0] = 1000
MUX1[3:0] = 0001
MUX1[3:0] = 0010
EMI
Filter
VREFP + VREFN
2
MUX1[3:0] = 0110 or
MUX1[3:0] = 1000
MUX1[3:0] = 0001
MUX1[3:0] = 0000
IN1N
From LOFFN
MUX1[3:0] = 0010
RLD_REF
MUX1[3:0] = 1001
MUX1[3:0] = 0011
MVDDN
MUX1[3:0] = 0100
TEMPN
RESP
MOD
To PGA1_INN
INT_TEST
TESTM
MUX1[3:0] = 1001
MUX1[3:0] = 0101
RESP_MODP/IN3P
RESP_MODN/IN3N
NOTE: MVDD monitor voltage supply depends on channel number; see the Supply Measurements (MVDDP, MVDDN) section.
Figure 14. Input Multiplexer Block for Both Channels
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Auxiliary Differential Input (IN3N, IN3P)
The IN3N and IN3P signals can be used as a third multiplexed differential input channel. These inputs can be
multiplexed to either of the ADC channels.
Temperature Sensor (TempP, TempN)
The ADS1191/2 contain an on-chip temperature sensor. This sensor uses two internal diodes with one diode
having a current density 16x that of the other, as shown in Figure 15. The difference in current densities of the
diodes yields a difference in voltage that is proportional to absolute temperature.
As a result of the low thermal resistance of the package to the printed circuit board (PCB), the internal device
temperature tracks the PCB temperature closely. Note that self-heating of the ADS1191/2 causes a higher
reading than the temperature of the surrounding PCB.
The scale factor of Equation 1 converts the temperature reading to °C. Before using this equation, the
temperature reading code must first be scaled to μV.
Temperature (°C) =
Temperature Reading (mV) - 168,000 mV
394 mV/°C
+ 25°C
(1)
Temperature Sensor Monitor
AVDD
1x
2x
To MUX TempP
To MUX TempN
8x
1x
AVSS
Figure 15. Measurement of the Temperature Sensor in the Input
Supply Measurements (MVDDP, MVDDN)
Setting CHnSET[2:0] = 011 sets the channel inputs to different supply voltages of the device. For channel 1
(MVDDP – MVDDN) is [0.5(AVDD + AVSS)]; for channel 2 (MVDDP – MVDDN) is DVDD/4. Note that to avoid
saturating the PGA while measuring power supplies, the gain must be set to '1'.
Lead-Off Excitation Signals (LoffP, LoffN)
The lead-off excitation signals are fed into the multiplexer before the switches. The comparators that detect the
lead-off condition are also connected to the multiplexer block before the switches. For a detailed description of
the lead-off block, refer to the Lead-Off Detection subsection in the ECG-Specific Functions section.
Auxiliary Single-Ended Input
The RLDIN pin is primarily used for routing the right leg drive signal to any of the electrodes in case the right leg
drive electrode falls off. However, the RLDIN pin can be used as a multiple single-ended input channel. The
signal at the RLDIN pin can be measured with respect to the voltage at the RLD_REF pin using either channel.
This measurement is done by setting the channel multiplexer setting MUXn[3:0] to '0010' in the CH1SET and
CH2SET registers.
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ANALOG INPUT
The analog input to the ADS1191/2 is fully differential. Assuming PGA = 1, the differential input (INP – INN) can
span between –VREF to +VREF. Refer to Table 4 for an explanation of the correlation between the analog input
and the digital codes. There are two general methods of driving the analog input of the ADS1191/2: single-ended
or differential, as shown in Figure 16 and Figure 17. Note that INP and INN are 180°C out-of-phase in the
differential input method. When the input is single-ended, the INN input is held at the common-mode voltage,
preferably at mid-supply. The INP input swings around the same common voltage and the peak-to-peak
amplitude is the (common-mode + 1/2 VREF) and the (common-mode – 1/2 VREF). When the input is differential,
the common-mode is given by (INP + INN)/2. Both the INP and INN inputs swing from (common-mode + 1/2
VREF to common-mode – 1/2 VREF). For optimal performance, it is recommended that the ADS1191/2 be used in
a differential configuration.
-1/2 VREF to
+1/2 VREF
VREF
Peak-to-Peak
Device
Device
Common
Voltage
Common
Voltage
Single-Ended Input
VREF
Peak-to-Peak
Differential Input
Figure 16. Methods of Driving the ADS1191/2: Single-Ended or Differential
CM + 1/2 VREF
+1/2 VREF
INP
CM Voltage
-1/2 VREF
INN = CM Voltage
CM - 1/2 VREF
t
Single-Ended Inputs
INP
CM + 1/2 VREF
+VREF
CM Voltage
CM - 1/2 VREF
INN
-VREF
t
Differential Inputs
(INP) + (INN)
, Common-Mode Voltage (Single-Ended Mode) = INN.
2
Input Range (Differential Mode) = (AINP - AINN) = 2 VREF.
Common-Mode Voltage (Differential Mode) =
Figure 17. Using the ADS1191/2 in the Single-Ended and Differential Input Modes
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PGA SETTINGS AND INPUT RANGE
The PGA is a differential input/differential output amplifier, as shown in Figure 18. It has seven gain settings (1,
2, 3, 4, 6, 8, and 12) that can be set by writing to the CHnSET register (see the CH1SET and CH2SET Registers
in the Register Map section for details). The ADS1191/2 have CMOS inputs and hence have negligible current
noise.
From MuxP
RS = 2 kW
PGA1P
PgaP
CP1
R2
150 kW
R1
60 kW
(for Gain = 6)
R2
150 kW
CFILTER
4.7 nF
RS = 2 kW
PgaN
PGA1N
From MuxN
CP2
Figure 18. PGA Implementation
The resistor string of the PGA that implements the gain has 360 kΩ of resistance for a gain of 6. This resistance
provides a current path across the outputs of the PGA in the presence of a differential input signal. This current
is in addition to the quiescent current specified for the device in the presence of a differential signal at the input.
The output of PGA is filtered by an RC filter before it goes to the ADC. The filter is formed by an internal resistor
RS = 2 kΩ and an external capacitor CFILTER (4.7 nF, typical). This filter acts as an anti-aliasing filter with the –3dB bandwidth of 8.4 kHz. The internal RS resistor is accurate to 15% so actual bandwidth will vary. This RC filter
also suppresses the glitch at the output of PGA caused by ADC sampling. The minimum value of CEXT that can
be used is 4 nF. A larger value CFILTER capacitor can be used for increased attenution at higher frequencies for
anti-aliasing purposes. The tradeoff is that a larger capacitor value gives degraded THD performance. See
Figure 19 for a plot showing the THD versus CFILTER value.
−85
THD (dB)
−90
−95
−100
−105
5
10
15
CFILTER (nF)
20
25
G025
Figure 19. THD versus CFILTER Value
Special care must be taken in PCB layout to minimize the parasitic capacitance CP1/CP2. The absolute value of
these capacitances must be less than 20 pF. Ideally, CFILTER should be placed right at the pins to minimize these
capacitors. Mismatch between these capacitors will lead to CMRR degradation. Assuming everything else is
perfectly matched, the 60 Hz CMRR as a function of this mismatch is given by Equation 2.
Gain
CMRR = 20log
2p ´ 2e3 ´ DCP ´ 60
(2)
where ΔCP = CP1 – CP2
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For example, a mismatch of 20 pF with a gain of 6 limits the CMRR to 112 dB. If ΔCP is small, then the CMRR is
limited by the PGA itself and is as specified in the Electrical Characteristics table. The PGA are chopped
internally at either 8, 32, or 64 kSPS. The digital decimation filter filters out the chopping ripple in the normal path
so the chopping ripple is not a concern. First-order filtering is provided by the RC filter at the PGA output.
Additional filtering may be needed to suppress the chopping ripple. If the PGA output is routed to other circuitry,
a 20-kΩ series resistance must be added in the path near the CFILTER capacitor. The routing should be matched
to maintain the CMRR performance.
Input Common-Mode Range
The usable input common-mode range of the front end depends on various parameters, including the maximum
differential input signal, supply voltage, PGA gain, etc. This range is described in Equation 3:
Gain VMAX_DIFF
Gain VMAX_DIFF
AVDD - 0.4 > CM > AVSS + 0.4 +
2
2
where:
VMAX_DIFF = maximum differential signal at the input of the PGA
CM = common-mode range
(3)
For example:
If VDD = 3 V, gain = 6, and VMAX_DIFF = 350 mV
Then 1.25 V < CM < 1.75 V
Input Differential Dynamic Range
The differential (INP – INN) signal range depends on the analog supply and reference used in the system. This
range is shown in Equation 4.
VREF
±VREF 2 VREF
Max (INP - INN) <
;
Full-Scale Range =
=
Gain
Gain
Gain
(4)
The 3-V supply, with a reference of 2.42 V and a gain of 6 for ECGs, is optimized for power with a differential
input signal of approximately 300 mV. For higher dynamic range, a 5-V supply with a reference of 4 V (set by the
VREF_4V bit of the CONFIG3 register) can be used to increase the differential dynamic range.
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ADC ΔΣ Modulator
Power Spectral Density (dB)
Each channel of the ADS1191/2 has a 16-bit ΔΣ ADC. This converter uses a second-order modulator optimized
for low-power applications. The modulator samples the input signal at the rate of fMOD = fCLK/4 or fCLK/16, as
determined by the CLK_DIV bit. In both cases, the sampling clock has a typical value of 128 kHz. As in the case
of any ΔΣ modulator, the noise of the ADS1191/2 is shaped until fMOD/2, as shown in Figure 20. The on-chip
digital decimation filters explained in the next section can be used to filter out the noise at higher frequencies.
These on-chip decimation filters also provide antialias filtering. This feature of the ΔΣ converters drastically
reduces the complexity of the analog antialiasing filters that are typically needed with nyquist ADCs.
0
−10
−20
−30
−40
−50
−60
−70
−80
−90
−100
−110
−120
−130
−140
−150
−160
0.001
0.01
0.1
Normalized Frequency (fIN/fMOD)
1
G001
Figure 20. Power Spectral Density (PSD) of a ΔΣ Modulator (4-Bit Quantizer)
DIGITAL DECIMATION FILTER
The digital filter receives the modulator output and decimates the data stream. By adjusting the amount of
filtering, tradeoffs can be made between resolution and data rate: filter more for higher resolution, filter less for
higher data rates. Higher data rates are typically used in ECG applications for implement software pace detection
and ac lead-off detection.
The digital filter on each channel consists of a third-order sinc filter. The decimation ratio on the sinc filters can
be adjusted by the DR bits in the CONFIG1 register (see the Register Map section for details). This setting is a
global setting that affects all channels and, therefore, in a device all channels operate at the same data rate.
Sinc Filter Stage (sinx/x)
The sinc filter is a variable decimation rate, third-order, low-pass filter. Data are supplied to this section of the
filter from the modulator at the rate of fMOD. The sinc filter attenuates the high-frequency noise of the modulator,
then decimates the data stream into parallel data. The decimation rate affects the overall data rate of the
converter.
Equation 5 shows the scaled Z-domain transfer function of the sinc filter.
½H(z)½ =
1 - Z- N
3
1 - Z- 1
(5)
The frequency domain transfer function of the sinc filter is shown in Equation 6.
sin
½H(f)½ =
Npf
fMOD
N ´ sin
3
pf
fMOD
where:
N = decimation ratio
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0
0
-20
-0.5
-40
-1
Gain (dB)
Gain (dB)
The sinc filter has notches (or zeroes) that occur at the output data rate and multiples thereof. At these
frequencies, the filter has infinite attenuation. Figure 21 shows the frequency response of the sinc filter and
Figure 22 shows the roll-off of the sinc filter. With a step change at input, the filter takes 3 tDR to settle. After a
rising edge of the START signal, the filter takes tSETTLE time to give the first data output. The settling time of the
filters at various data rates are discussed in the START subsection of the SPI Interface section. Figure 23 and
Figure 24 show the filter transfer function until fMOD/2 and fMOD/16, respectively, at different data rates. Figure 25
shows the transfer function extended until 4 fMOD. It can be seen that the passband of the ADS1191/2 repeats
itself at every fMOD. The input R-C anti-aliasing filters in the system should be chosen such that any interference
in frequencies around multiples of fMOD are attenuated sufficiently.
-60
-80
-1.5
-2
-100
-2.5
-120
-3
-140
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0
0.05
Normalized Frequency (fIN/fDR)
0.2
0.25
0.3
0.35
Figure 22. INL vs PGA Gain
0
0
DR[0:2] = 000
DR[0:2] = 000
-20
DR[0:2] = 110
-40
DR[0:2] = 110
-40
Gain (dB)
Gain (dB)
0.15
Normalized Frequency (fIN/fDR)
Figure 21. THD vs Frequency
-20
0.1
-60
-80
-60
-80
-100
-100
-120
-120
-140
-140
0
0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
0
0.01
Normalized Frequency (fIN/fMOD)
Figure 23. Transfer Function of On-Chip
Decimation Filters Until fMOD/2
0.02
0.03
0.04
0.05
0.06
0.07
Normalized Frequency (fIN/fMOD)
Figure 24. Transfer Function of On-Chip
Decimation Filters Until fMOD/16
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DR[0:2] = 000
DR[0:2] = 110
-10
Gain (dB)
-30
-50
-70
-90
-110
-130
0
0.5
1
1.5
2
2.5
3
3.5
4
Normalized Frequency (fIN/fMOD)
Figure 25. Transfer Function of On-Chip Decimation Filters
Until 4fMOD for DR[0:2] = 000 and DR[0:2] = 110
REFERENCE
Figure 26 shows a simplified block diagram of the internal reference of the ADS1191/2. The reference voltage is
generated with respect to AVSS. The VREFN pin must always be connected to AVSS.
1 mF
VCAP1
(1)
R1
2.42 V or
4.033 V
Bandgap
VREFP
(1)
R3
10 mF
R2
0.1 mF
(1)
VREFN
AVSS
To ADC Reference Inputs
(1) For VREF = 2.42 V: R1 = 100 kΩ, R2 = 200 kΩ, and R3 = 200 kΩ. For VREF = 4.033 V: R1 = 84 kΩ, R2 = 120 kΩ, and R3 = 280 kΩ.
Figure 26. Internal Reference
The external band-limiting capacitors determine the amount of reference noise contribution. For high-end ECG
systems, the capacitor values should be chosen such that the bandwidth is limited to less than 10 Hz, so that the
reference noise does not dominate the system noise. When using a 3-V analog supply, the internal reference
must be set to 2.42 V. In case of a 5-V analog supply, the internal reference can be set to 4.033 V by setting the
VREF_4V bit in the CONFIG2 register.
Alternatively, the internal reference buffer can be powered down and VREFP can be applied externally. Figure 27
shows a typical external reference drive circuitry. Power-down is controlled by the PD_REFBUF bit in the
CONFIG3 register. This power-down is also used to share internal references when two devices are cascaded.
By default, the device wakes up in external reference mode.
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100 kW
10 pF
+5 V
0.1 mF
100 W
+5 V
VIN
10 mF
OUT
22 mF
REF5025
TRIM
To VREFP Pin
OPA211
100 W
0.1 mF
100 mF
22 mF
Figure 27. External Reference Driver
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CLOCK
The ADS1191/2 provide two different methods for device clocking: internal and external. Internal clocking is
ideally suited for low-power, battery-powered systems. The internal oscillator is trimmed for accuracy at room
temperature. Over the specified temperature range the accuracy varies; see the Electrical Characteristics. Clock
selection is controlled by the CLKSEL pin and the CLK_EN register bit.
The CLKSEL pin selects either the internal or external clock. The CLK_EN bit in the CONFIG1 register enables
and disables the oscillator clock to be output in the CLK pin. A truth table for these two pins is shown in Table 3.
The CLK_EN bit is useful when multiple devices are used in a daisy-chain configuration. It is recommended that
during power-down the external clock be shut down to save power.
Table 3. CLKSEL Pin and CLK_EN Bit
CLKSEL PIN
CONFIG1.CLK_EN
BIT
CLOCK SOURCE
CLK PIN STATUS
0
X
External clock
Input: external clock
1
0
Internal clock oscillator
3-state
1
1
Internal clock oscillator
Output: internal clock oscillator
The ADS1191/2 have the option to choose between two different external clock frequencies (512 kHz or
2.048 MHz). This frequency is selected by setting the CLK_DIV bit (bit 6) in the LOFF_STAT register. The
modulator must be clocked at 128 kHz, regardless of the external clock frequency. Figure 28 shows the
relationship between the external clock (fCLK) and the modulator clock (fMOD). The default mode of operation is
fCLK = 512 kHz. The higher frequency option has only been provided to allow the SPI to run at a higher speed.
SCLK can be only twice the speed of fCLK during a register read and/or write.
fCLK
Frequency
Divider
Divide-By-4
fMOD
Frequency
Divider
Divide-By-16
CLK_DIV
(Bit 6 of LOFF_STAT
Register)
Figure 28. Relationship Between External Clock (fCLK) and Modulator Clock (fMOD)
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DATA FORMAT
The ADS1191/2 outputs 16 bits of data per channel in binary twos complement format, MSB first. The LSB has a
weight of VREF/(215 – 1). A positive full-scale input produces an output code of 7FFFh and the negative full-scale
input produces an output code of 8000h. The output clips at these codes for signals exceeding full-scale. Table 4
summarizes the ideal output codes for different input signals. All 16 bits toggle when the analog input is at
positive or negative full-scale.
Table 4. Ideal Output Code versus Input Signal
INPUT SIGNAL, VIN
(AINP – AINN)
IDEAL OUTPUT CODE (1)
≥ VREF
7FFFh
15
+VREF/(2
(1)
– 1)
0001h
0
0000h
–VREF/(215 – 1)
FFFFh
≤ –VREF (215/215 – 1)
8000h
Excludes effects of noise, linearity, offset, and gain error.
SPI INTERFACE
The SPI-compatible serial interface consists of four signals: CS, SCLK, DIN, and DOUT. The interface reads
conversion data, reads and writes registers, and controls the ADS1191/2 operation. The DRDY output is used as
a status signal to indicate when data are ready. DRDY goes low when new data are available.
Chip Select (CS)
Chip select (CS) selects the ADS1191/2 for SPI communication. CS must remain low for the entire duration of
the serial communication. After the serial communication is finished, always wait four or more tCLK cycles before
taking CS high. When CS is taken high, the serial interface is reset, SCLK and DIN are ignored, and DOUT
enters a high-impedance state. DRDY asserts when data conversion is complete, regardless of whether CS is
high or low.
Serial Clock (SCLK)
SCLK is the serial peripheral interface (SPI) serial clock. It is used to shift in commands and shift out data from
the device. The serial clock (SCLK) features a Schmitt-triggered input and clocks data on the DIN and DOUT
pins into and out of the ADS1191/2. Even though the input has hysteresis, it is recommended to keep SCLK as
clean as possible to prevent glitches from accidentally forcing a clock event. The absolute maximum limit for
SCLK is specified in the Serial Interface Timing table. When shifting in commands with SCLK, make sure that the
entire set of SCLKs is issued to the device. Failure to do so could result in the device serial interface being
placed into an unknown state, requiring CS to be taken high to recover.
For a single device, the minimum speed needed for the SCLK depends on the number of channels, number of
bits of resolution, and output data rate. (For multiple cascaded devices, see the Cascade Mode subsection of the
Multiple Device Configuration section.)
tSCLK < (tDR – 4 tCLK)/(NBITSNCHANNELS + 24)
(7)
For example, if the ADS1191/2 is used in a 500-SPS mode (two channels, 16-bit resolution), the minimum SCLK
speed is approximately 36 kHz.
Data retrieval can be done either by putting the device in RDATAC mode or by issuing a RDATA command for
data on demand. The above SCLK rate limitation applies to RDATAC. For the RDATA command, the limitation
applies if data must be read in between two consecutive DRDY signals. The above calculation assumes that
there are no other commands issued in between data captures. SCLK can only be twice the speed of fCLK during
register reads and writes. For faster SPI interface, use fCLK = 2.048 MHz and set the CLK_DIV register bit (in the
LOFF_STAT register) to '1'.
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Data Input (DIN)
The data input pin (DIN) is used along with SCLK to communicate with the ADS1191/2 (opcode commands and
register data). The device latches data on DIN on the falling edge of SCLK.
Data Output (DOUT)
The data output pin (DOUT) is used with SCLK to read conversion and register data from the ADS1191/2. Data
on DOUT are shifted out on the rising edge of SCLK. DOUT goes to a high-impedance state when CS is high. In
read data continuous mode (see the SPI Command Definitions section for more details), the DOUT output line
also indicates when new data are available. This feature can be used to minimize the number of connections
between the device and the system controller.
Figure 29 shows the data output protocol for ADS1192.
DRDY
CS
SCLK
DOUT
STAT
CH1
CH2
16-Bit
16-Bit
16-Bit
DIN
Figure 29. SPI Bus Data Output for the ADS1192 (Two Channels)
Data Retrieval
Data retrieval can be accomplished in one of two methods. The read data continuous command (see the
RDATAC: Read Data Continuous section) can be used to set the device in a mode to read the data continuously
without sending opcodes. The read data command (see the RDATA: Read Data section) can be used to read
just one data output from the device (see the SPI Command Definitions section for more details). The conversion
data are read by shifting the data out on DOUT. The MSB of the data on DOUT is clocked out on the first SCLK
rising edge. DRDY returns to high on the first SCLK falling edge. DIN should remain low for the entire read
operation.
The number of bits in the data output depends on the number of channels and the number of bits per channel.
For the ADS1191/2, the number of data outputs is (16 status bits + 16 bits × 2 channels) = 48 bits. The format of
the 16 status bits is (1100 + LOFF_STAT[4:0] + GPIO[1:0] + 5 zeros). The data format for each channel data are
twos complement and MSB first. When channels are powered down using the user register setting, the
corresponding channel output is set to '0'. However, the sequence of channel outputs remains the same.
The ADS1191/2 also provide a multiple readback feature. The data can be read out multiple times by simply
giving more SCLKs, in which case the MSB data byte repeats after reading the last byte.
Data Ready (DRDY)
DRDY is an output. When it transitions low, new conversion data are ready. The CS signal has no effect on the
data ready signal. The behavior of DRDY is determined by whether the device is in RDATAC mode or the
RDATA command is being used to read data on demand. (See the RDATAC: Read Data Continuous and
RDATA: Read Data subsections of the SPI Command Definitions section for further details).
When reading data with the RDATA command, the read operation can overlap the occurrence of the next DRDY
without data corruption.
The START pin or the START command is used to place the device either in normal data capture mode or pulse
data capture mode.
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Figure 30 shows the relationship between DRDY, DOUT, and SCLK during data retrieval (in case of an
ADS1191/2 with a selected data rate that gives 16-bit resolution). DOUT is latched out at the rising edge of
SCLK. DRDY is pulled high at the falling edge of SCLK. Note that DRDY goes high on the first falling edge SCLK
regardless of the status of the CS signal and regardless of whether data are being retrieved from the device or a
command is being sent through the DIN pin.
DRDY
Bit 55
DOUT
Bit 54
Bit 53
SCLK
Figure 30. DRDY with Data Retrieval (CS = 0)
GPIO
The ADS1191/2 have a total of two general-purpose digital I/O (GPIO) pins available in the normal mode of
operation. The digital I/O pins are individually configurable as either inputs or as outputs through the GPIOC bits
register. The GPIOD bits in the GPIO register control the level of the pins. When reading the GPIOD bits, the
data returned are the logic level of the pins, whether they are programmed as inputs or outputs. When the GPIO
pin is configured as an input, a write to the corresponding GPIOD bit has no effect. When configured as an
output, a write to the GPIOD bit sets the output value.
If configured as inputs, these pins must be driven (do not float). The GPIO pins are set as inputs after power-on
or after a reset. Figure 31 shows the GPIO port structure. The pins should be shorted to DGND with a series
resistor if not used.
GPIO Data (read)
GPIO Pin
GPIO Data (write)
GPIO Control
Figure 31. GPIO Port Pin
Power-Down/Reset (PWDN/RESET)
The PWDN/RESET pins are shared. If PWDN/RESET is held low for longer than 29 tMODs, the device is powered
down. The implementation is such that the device is always reset when PWDN/RESET makes a transition from
high to low. If the device is powered down it is reset first and then if 210 clock elapses it is powered down. Hence,
when powering up the device from a power-down state, all registers must be rewritten.
There are two methods to reset the ADS1191/2: pull the PWDN/RESET pin low, or send the RESET opcode
command. When using the PWDN/RESET pin, take it low to force a reset. Make sure to follow the minimum
pulse width timing specifications before taking the PWDN/RESET pin back high. The RESET command takes
effect on the eighth SCLK falling edge of the opcode command. On reset it takes 18 tCLK cycles to complete
initialization of the configuration registers to the default states and start the conversion cycle. Note that an
internal RESET is automatically issued to the digital filter whenever the CONFIG1 register is set to a new value
with a WREG command.
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START
The START pin must be set high or the START command sent to begin conversions. When START is low or if
the START command has not been sent, the device does not issue a DRDY signal (conversions are halted).
When using the START opcode to control conversion, hold the START pin low. The ADS1191/2 feature two
modes to control conversion: continuous mode and single-shot mode. The mode is selected by SINGLE_SHOT
(bit 7 of the CONFIG1 register). In multiple device configurations the START pin is used to synchronize devices
(see the Multiple Device Configuration subsection of the SPI Interface section for more details).
Settling Time
The settling time (tSETTLE) is the time it takes for the converter to output fully settled data when the START signal
is pulled high. Once START is pulled high, DRDY is also pulled high. The next falling edge of DRDY indicates
that data are ready. Figure 32 shows the timing diagram and Table 5 shows the settling time for different data
rates. The settling time depends on fCLK and the decimation ratio (controlled by the DR[2:0] bits in the CONFIG1
register). Table 4 shows the settling time as a function of tCLK. Note that when START is held high and there is a
step change in the input signal, it takes 3 tDR for the filter to settle to the new value. Settled data are available on
the fourth DRDY pulse. Settling time number uncertainty is one tMOD cycle. Therefore, it is recommended to add
one tMOD cycle delay before issuing SCLK to retrieve data.
tSETTLE
START Pin
or
START Opcode
DIN
tDR
4 / fCLK
DRDY
(1) Settling time uncertainty is one tMOD cycle.
Figure 32. Settling Time
Table 5. Settling Time for Different Data Rates
(1)
(2)
28
DR[2:0]
SETTLING TIME (1)
UNIT (2)
000
4100
tMOD
001
2052
tMOD
010
1028
tMOD
011
516
tMOD
100
260
tMOD
101
132
tMOD
110
68
tMOD
111
—
—
Settling time uncertainty is one tMOD cycle.
tMOD = 4 tCLK for CLK_DIV = 0 and tMOD = 16 tCLK for CLK_DIV = 1.
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Continuous Mode
Conversions begin when the START pin is taken high or when the START opcode command is sent. As seen in
Figure 33, the DRDY output goes high when conversions are started and goes low when data are ready.
Conversions continue indefinitely until the START pin is taken low or the STOP opcode command is transmitted.
When the START pin is pulled low or the stop command is issued, the conversion in progress is allowed to
complete. Figure 34 and Table 6 show the required timing of DRDY to the START pin and the START/STOP
opcode commands when controlling conversions in this mode. To keep the converter running continuously, the
START pin can be permanently tied high. Note that when switching from pulse mode to continuous mode, the
START signal is pulsed or a STOP command must be issued followed by a START command. This conversion
mode is ideal for applications that require a fixed continuous stream of conversions results.
START Pin
or
or
(1)
DIN
(1)
START
Opcode
STOP
Opcode
tDR
tSETTLE
DRDY
(1)
START and STOP opcode commands take effect on the seventh SCLK falling edge at the end of the opcode
transmission.
Figure 33. Continuous Conversion Mode
tSDSU
DRDY and DOUT
tDSHD
START Pin
or
STOP Opcode
(1)
STOP(1)
STOP(1)
START and STOP commands take effect on the seventh SCLK falling edge at the end of the opcode transmission.
Figure 34. START to DRDY Timing
Table 6. Timing Characteristics for Figure 34 (1)
SYMBOL
(1)
DESCRIPTION
MIN
UNIT
tSDSU
START pin low or STOP opcode to DRDY setup time
to halt further conversions
8
tMOD
tDSHD
START pin low or STOP opcode to complete current
conversion
8
tMOD
START and STOP commands take effect on the seventh SCLK falling edge at the end of the opcode transmission.
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Single-Shot Mode
The single-shot mode is enabled by setting the SINGLE_SHOT bit in the CONFIG1 register to '1'. In single-shot
mode, the ADS1191/2 perform a single conversion when the START pin is taken high or when the START
opcode command is sent. As seen in Figure 34, when a conversion is complete, DRDY goes low and further
conversions are stopped. Regardless of whether the conversion data are read or not, DRDY remains low. To
begin a new conversion, take the START pin low and then back high, or transmit the START opcode again.
When switching from continuous mode to pulse mode, make sure the START signal is pulsed or issue a STOP
command followed by a START command.
This conversion mode is provided for applications that require non-standard or non-continuous data rates.
Issuing a START command or toggling the START pin high resets the digital filter, effectively dropping the data
rate by a factor of four. Note that this mode leaves the system more susceptible to aliasing effects, requiring
more complex analog anti-aliasing filters at the inputs. Loading on the host processor increases because it must
toggle the START pin or send a START command to initiate a new conversion cycle.
START
tSETTLE
4 / fCLK
Data Updating
4 / fCLK
DRDY
Figure 35. DRDY with No Data Retrieval in Single-Shot Mode
MULTIPLE DEVICE CONFIGURATION
The ADS1191/2 are designed to provide configuration flexibility when multiple devices are used in a system. The
serial interface typically needs four signals: DIN, DOUT, SCLK, and CS. With one additional chip select signal
per device, multiple devices can be connected together. The number of signals needed to interface n devices is
3 + n.
The right leg drive amplifiers can be daisy-chained as explained in the RLD Configuration with Multiple Devices
subsection of the ECG-Specific Functions section. To use the internal oscillator in a daisy-chain configuration,
one of the devices must be set as the master for the clock source with the internal oscillator enabled (CLKSEL
pin = 1) and the internal oscillator clock brought out of the device by setting the CLK_EN register bit to '1'. This
master device clock is used as the external clock source for the other devices.
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When using multiple devices, the devices can be synchronized with the START signal. The delay from START to
the DRDY signal is fixed for a fixed data rate (see the START subsection of the SPI Interface section for more
details on the settling times). Figure 36 shows the behavior of two devices when synchronized with the START
signal.
Device1
START
START1
CLK
DRDY
DRDY1
CLK
Device2
START2
DRDY
DRDY2
CLK
CLK
Note 1
START
DRDY1
Note 2
DRDY2
(1) Start pulse must be at least one tMOD cycle wide.
(2) Settling time number uncertainty is one tMOD cycle.
Figure 36. Synchronizing Multiple Converters
Standard Mode
Figure 37 shows a configuration with two devices cascaded together. One of the devices is an ADS1192 (twochannel) and the other is an ADS1192 (two-channel). Together, they create a system with four channels. DOUT,
SCLK, and DIN are shared. Each device has its own chip select. When a device is not selected by the
corresponding CS being driven to logic 1, the DOUT of this device is high-impedance. This structure allows the
other device to take control of the DOUT bus.
(1)
START
START
CLK
CLK
DRDY
CS
INT
GPO0
GPO1
Device 2
SCLK
SCLK
DIN
MOSI
DOUT
MISO
Host Processor
START
CLK
DRDY
CS
SCLK
Device 1
DIN
DOUT
Figure 37. Multiple Device Configurations
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SPI COMMAND DEFINITIONS
The ADS1191/2 provide flexible configuration control. The opcode commands, summarized in Table 7, control
and configure the operation of the ADS1191/2. The opcode commands are stand-alone, except for the register
read and register write operations that require a second command byte plus data. CS can be taken high or held
low between opcode commands but must stay low for the entire command operation (especially for multi-byte
commands). System opcode commands and the RDATA command are decoded by the ADS1191/2 on the
seventh falling edge of SCLK. The register read/write opcodes are decoded on the eighth SCLK falling edge. Be
sure to follow SPI timing requirements when pulling CS high after issuing a command.
Table 7. Command Definitions
COMMAND
DESCRIPTION
FIRST BYTE
SECOND BYTE
System Commands
WAKEUP
Wake-up from standby mode
0000 0010 (02h)
STANDBY
Enter standby mode
0000 0100 (04h)
RESET
Reset the device
0000 0110 (06h)
START
Start/restart (synchronize) conversions
0000 1000 (08h)
STOP
Stop conversion
0000 1010 (0Ah)
OFFSETCAL
Channel offset calibration
0001 1010 (1Ah)
Data Read Commands
RDATAC
Enable Read Data Continuous mode.
This mode is the default mode at power-up. (1)
0001 0000 (10h)
SDATAC
Stop Read Data Continuously mode
0001 0001 (11h)
RDATA
Read data by command; supports multiple read back.
0001 0010 (12h)
Register Read Commands
RREG
WREG
(1)
(2)
Read n nnnn registers starting at address r rrrr
001r rrrr (2xh) (2)
000n nnnn (2)
Write n nnnn registers starting at address r rrrr
(2)
000n nnnn (2)
010r rrrr (4xh)
When in RDATAC mode, the RREG command is ignored.
n nnnn = number of registers to be read/written – 1. For example, to read/write three registers, set n nnnn = 0 (0010). r rrrr = starting
register address for read/write opcodes.
WAKEUP: Exit STANDBY Mode
This opcode exits the low-power standby mode; see the STANDBY: Enter STANDBY Mode subsection of the
SPI Command Definitions section. Time is required when exiting standby mode (see the Electrical
Characteristics for details). There are no restrictions on the SCLK rate for this command and it can be
issued any time. Any following command must be sent after 4 tCLK cycles.
STANDBY: Enter STANDBY Mode
This opcode command enters the low-power standby mode. All parts of the circuit are shut down except for the
reference section. The standby mode power consumption is specified in the Electrical Characteristics. There are
no restrictions on the SCLK rate for this command and it can be issued any time. Do not send any other
command other than the wakeup command after the device enters the standby mode.
RESET: Reset Registers to Default Values
This command resets the digital filter cycle and returns all register settings to the default values. See the Reset
(RESET) subsection of the SPI Interface section for more details. There are no restrictions on the SCLK rate
for this command and it can be issued any time. It takes 9 fMOD cycles to execute the RESET command.
Avoid sending any commands during this time.
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START: Start Conversions
This opcode starts data conversions. Tie the START pin low to control conversions by command. If conversions
are in progress this command has no effect. The STOP opcode command is used to stop conversions. If the
START command is immediately followed by a STOP command then have a gap of 4 tCLK cycles between them.
When the START opcode is sent to the device, keep the START pin low until the STOP command is issued.
(See the START subsection of the SPI Interface section for more details.) There are no restrictions on the
SCLK rate for this command and it can be issued any time.
STOP: Stop Conversions
This opcode stops conversions. Tie the START pin low to control conversions by command. When the STOP
command is sent, the conversion in progress completes and further conversions are stopped. If conversions are
already stopped, this command has no effect. There are no restrictions on the SCLK rate for this command and it
can be issued any time.
OFFSETCAL: Channel Offset Calibration
This command is used to cancel the channel offset. The CALIB_ON bit in the MISC2 register must be set to '1'
before issuing this command. OFFSETCAL must be executed every time there is a change in the PGA gain
settings.
RDATAC: Read Data Continuous
This opcode enables the output of conversion data on each DRDY without the need to issue subsequent read
data opcodes. This mode places the conversion data in the output register and may be shifted out directly. The
read data continuous mode is the default mode of the device and the device defaults in this mode on power-up.
RDATAC mode is cancelled by the Stop Read Data Continuous command. If the device is in RDATAC mode, an
SDATAC command must be issued before any other commands can be sent to the device. There is no
restriction on the SCLK rate for this command. However, the subsequent data retrieval SCLKs or the SDATAC
opcode command should wait at least 4 tCLK cycles. The timing for RDATAC is shown in Figure 38. As Figure 38
shows, there is a keep out zone of 4 tCLK cycles around the DRDY pulse where this command cannot be issued
in. If no data are retrieved from the device, DOUT and DRDY behave similarly in this mode. To retrieve data from
the device after the RDATAC command is issued, make sure either the START pin is high or the START
command is issued. Figure 38 shows the recommended way to use the RDATAC command. RDATAC is ideally
suited for applications such as data loggers or recorders where registers are set once and do not need to be reconfigured.
START
DRDY
(1)
tUPDATE
CS
SCLK
RDATAC Opcode
DIN
Hi-Z
DOUT
Status Register + 2-Channel Data
(1)
Next Data
tUPDATE = 4 * tCLK. Do not read data during this time.
Figure 38. RDATAC Usage
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SDATAC: Stop Read Data Continuous
This opcode cancels the Read Data Continuous mode. There is no restriction on the SCLK rate for this
command, but the following command must wait for 4 tCLK cycles.
RDATA: Read Data
Issue this command after DRDY goes low to read the conversion result (in Stop Read Data Continuous mode).
There is no restriction on the SCLK rate for this command, and there is no wait time needed for the subsequent
commands or data retrieval SCLKs. To retrieve data from the device after the RDATA command is issued, make
sure either the START pin is high or the START command is issued. When reading data with the RDATA
command, the read operation can overlap the occurrence of the next DRDY without data corruption. Figure 39
shows the recommended way to use the RDATA command. RDATA is best suited for ECG- and EEG-type
systems where register setting must be read or changed often between conversion cycles.
START
DRDY
CS
SCLK
RDATA Opcode
DIN
RDATA Opcode
Hi-Z
DOUT
Status Register+ 8-Channel Data (216 Bits)
Figure 39. RDATA Usage
Sending Multi-Byte Commands
The ADS1191/2 serial interface decodes commands in bytes and requires 4 tCLK cycles to decode and execute.
Therefore, when sending multi-byte commands, a 4 tCLK period must separate the end of one byte (or opcode)
and the next.
Assume CLK is 512 kHz, then tSDECODE (4 tCLK) is 7.8125 µs. When SCLK is 16 MHz, one byte can be
transferred in 500 ns. This byte transfer time does not meet the tSDECODE specification; therefore, a delay must be
inserted so the end of the second byte arrives 7.3125 µs later. If SCLK is 1 MHz, one byte is transferred in 8 µs.
Because this transfer time exceeds the tSDECODE specification, the processor can send subsequent bytes without
delay. In this later scenario, the serial port can be programmed to cease single-byte transfer per cycle to multiple
bytes.
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RREG: Read From Register
This opcode reads register data. The Register Read command is a two-byte opcode followed by the output of the
register data. The first byte contains the command opcode and the register address. The second byte of the
opcode specifies the number of registers to read – 1.
First opcode byte: 001r rrrr, where r rrrr is the starting register address.
Second opcode byte: 000n nnnn, where n nnnn is the number of registers to read – 1.
The 17th SCLK rising edge of the operation clocks out the MSB of the first register, as shown in Figure 40. When
the device is in read data continuous mode it is necessary to issue a SDATAC command before the RREG
command can be issued. The RREG command can be issued any time. However, because this command is a
multi-byte command, there are restrictions on the SCLK rate depending on the way the SCLKs are issued. See
the Serial Clock (SCLK) subsection of the SPI Interface section for more details. Note that CS must be low for
the entire command.
CS
1
9
17
25
SCLK
DIN
OPCODE 1
OPCODE 2
REG DATA
DOUT
REG DATA + 1
Figure 40. RREG Command Example: Read Two Registers Starting from Register 00h (ID Register)
(OPCODE 1 = 0010 0000, OPCODE 2 = 0000 0001)
WREG: Write to Register
This opcode writes register data. The Register Write command is a two-byte opcode followed by the input of the
register data. The first byte contains the command opcode and the register address.
The second byte of the opcode specifies the number of registers to write – 1.
First opcode byte: 010r rrrr, where r rrrr is the starting register address.
Second opcode byte: 000n nnnn, where n nnnn is the number of registers to write – 1.
After the opcode bytes, the register data follows (in MSB-first format), as shown in Figure 41. The WREG
command can be issued any time. However, because this command is a multi-byte command, there are
restrictions on the SCLK rate depending on the way the SCLKs are issued. See the Serial Clock (SCLK)
subsection of the SPI Interface section for more details. Note that CS must be low for the entire command.
CS
1
9
17
25
SCLK
DIN
OPCODE 1
OPCODE 2
REG DATA 1
REG DATA 2
DOUT
Figure 41. WREG Command Example: Write Two Registers Starting from 00h (ID Register)
(OPCODE 1 = 0100 0000, OPCODE 2 = 0000 0001)
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REGISTER MAP
Table 8 describes the various ADS1191/2 registers.
Table 8. Register Assignments
ADDRESS
RESET
VALUE
(Hex)
REGISTER
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
XX
REV_ID7
REV_ID6
REV_ID5
1
0
0
REV_ID1
REV_ID0
Device Settings (Read-Only Registers)
00h
ID
Global Settings Across Channels
01h
CONFIG1
02
SINGLE_
SHOT
0
0
0
0
DR2
DR1
DR0
02h
CONFIG2
80
1
PDB_LOFF_
COMP
PDB_REFBUF
VREF_4V
CLK_EN
0
INT_TEST
TEST_FREQ
03h
LOFF
10
COMP_TH2
COMP_TH1
COMP_TH0
1
ILEAD_OFF1
ILEAD_OFF0
0
FLEAD_OFF
Channel-Specific Settings
04h
CH1SET
00
PD1
GAIN1_2
GAIN1_1
GAIN1_0
MUX1_3
MUX1_2
MUX1_1
MUX1_0
05h
CH2SET
00
PD2
GAIN2_2
GAIN2_1
GAIN2_0
MUX2_3
MUX2_2
MUX2_1
MUX2_0
06h
RLD_SENS
00
0
0
PDB_RLD
RLD_LOFF_
SENS
RLD2N
RLD2P
RLD1N
RLD1P
07h
LOFF_SENS
00
0
0
FLIP2
FLIP1
LOFF2N
LOFF2P
LOFF1N
LOFF1P
08h
LOFF_STAT
00
0
CLK_DIV
0
RLD_STAT
(read only)
IN2N_OFF
IN2P_OFF
IN1N_OFF
IN1P_OFF
0
GPIO and Other Registers
09h
MISC1
00
0
0
0
0
0
0
1
0Ah
MISC2
02
CALIB_ON
0
0
0
0
0
RLDREF_INT
0
0Bh
GPIO
0C
0
0
0
0
GPIOC2
GPIOC1
GPIOD2
GPIOD1
User Register Description
ID: ID Control Register (Factory-Programmed, Read-Only)
Address = 00h
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
REV_ID7
REV_ID6
REV_ID5
1
0
0
REV_ID1
REV_ID0
The ID Control Register is programmed during device manufacture to indicate device characteristics.
Bits[7:5]
REV_ID[7:5]: Revision identification
000 = Reserved
001 = Reserved
010 = ADS1x9x device
011 = ADS1292R device
100 = Reserved
101 = Reserved
110 = Reserved
111 = Reserved
Bit 4
Reads high
Bits[3:2]
Reads low
Bits[1:0]
REV_ID[1:0]: Revision identification
00
01
10
11
36
= ADS1191
= ADS1192
= ADS1291
= ADS1292/2R
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CONFIG1: Configuration Register 1
Address = 01h
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
SINGLE_SHOT
0
0
0
0
DR2
DR1
DR0
Configuration Register 1 configures each ADC channel sample rate.
Bit 7
SINGLE_SHOT: Single-shot conversion
This bit sets the conversion mode
0 = Continuous conversion mode (default)
1 = Single-shot mode
Bits[6:3]
Must be set to '0'
Bits[2:0]
DR[2:0]: Channel oversampling ratio
These bits determine the oversampling ratio of both channel 1 and channel 2.
(1)
BIT
OVERSAMPLING RATIO
DATA RATE (1)
000
fMOD/1024
125 SPS
001
fMOD/512
250 SPS
010
fMOD/256
500 SPS (default)
011
fMOD/128
1 kSPS
100
fMOD/64
2 kSPS
101
fMOD/32
4 kSPS
110
fMOD/16
8 kSPS
111
Do not use
Do not use
fCLK = 512 kHz and CLK_DIV = 0 or fCLK = 2.048 MHz and CLK_DIV = 1.
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CONFIG2: Configuration Register 2
Address = 02h
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
1
PDB_LOFF_
COMP
PDB_REFBUF
VREF_4V
CLK_EN
0
INT_TEST
TEST_FREQ
Configuration Register 2 configures the test signal, clock, reference, and LOFF buffer.
Bit 7
Must be set to '1'
Bit 6
PDB_LOFF_COMP: Lead-off comparator power-down
This bit powers down the lead-off comparators.
0 = Lead-off comparators disabled (default)
1 = Lead-off comparators enabled
Bit 5
PDB_REFBUF: Reference buffer power-down
This bit powers down the internal reference buffer so that the external reference can be used.
0 = Reference buffer is powered down (default)
1 = Reference buffer is enabled
Bit 4
VREF_4V: Enables 4-V reference
This bit chooses between 2.42-V and 4.033-V reference.
0 = 2.42-V reference (default)
1 = 4.033-V reference
Bit 3
CLK_EN: CLK connection
This bit determines if the internal oscillator signal is connected to the CLK pin when an internal oscillator is used.
0 = Oscillator clock output disabled (default)
1 = Oscillator clock output enabled
Bit 2
Must be set to '0'
Bit 1
INT_TEST: Test signal selection
This bit determines whether the test signal is turned on or off.
0 = Off (default)
1 = On; amplitude = ±(VREFP – VREFN)/2420
Bit 0
TEST_FREQ: Test signal frequency.
This bit determines the test signal frequency.
0 = At dc (default)
1 = Square wave at 1 Hz
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LOFF: Lead-Off Control Register
Address = 03h
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
COMP_TH2
COMP_TH1
COMP_TH0
1
ILEAD_OFF1
ILEAD_OFF0
0
FLEAD_OFF
The Lead-Off Control Register configures the Lead-Off detection operation.
Bits[7:5]
COMP_TH[2:0]: Lead-off comparator threshold
These bits determine the lead-off comparator threshold. See the Lead-Off Detection subsection of the ECG-Specific
Functions section for a detailed description.
Comparator positive side
000 = 95% (default)
001 = 92.5%
010 = 90%
011 = 87.5%
100 = 85%
101 = 80%
110 = 75%
111 = 70%
Comparator negative side
000 = 5% (default)
001 = 7.5%
010 = 10%
011 = 12.5%
100 = 15%
101 = 20%
110 = 25%
111 = 30%
Bit 4
Must be set to '1'
Bits[3:2]
ILEAD_OFF[1:0]: Lead-off current magnitude
These bits determine the magnitude of current for the current lead-off mode.
00 = 6 nA (default)
01 = 22 nA
10 = 6 µA
11 = 22 µA
Bit 1
Must be set to '0'
Bit 0
FLEAD_OFF: Lead-off frequency
This bit selects ac or dc lead-off.
0 = At dc lead-off detect (default)
1 = At ac lead-off detect at fDR/4 (500 Hz for an 2-kHz output rate)
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CH1SET: Channel 1 Settings
Address = 04h
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
PD1
GAIN1_2
GAIN1_1
GAIN1_0
MUX1_3
MUX1_2
MUX1_1
MUX1_0
The CH1SET Control Register configures the power mode, PGA gain, and multiplexer settings channels. See the
Input Multiplexer section for details.
Bit 7
PD1: Channel 1 power-down
0 = Normal operation (default)
1 = Channel 1 power-down
Bits[6:4]
GAIN1[2:0]: Channel 1 PGA gain setting
These bits determine the PGA gain setting for channel 1.
000 = 6 (default)
001 = 1
010 = 2
011 = 3
100 = 4
101 = 8
110 = 12
111 = Not available
Bits[3:0]
MUX1[3:0]: Channel 1 input selection
These bits determine the channel 1 input selection.
0000 = Normal electrode input (default)
0001 = Input shorted (for offset measurements)
0010 = RLD_MEASURE
0011 = MVDD for supply measurement
0100 = Temperature sensor
0101 = Test signal
0110 = RLD_DRP (positive input is connected to RLDIN)
0111 = RLD_DRM (negative input is connected to RLDIN)
1000 = RLD_DRPM (both positive and negative inputs are connected to RLDIN)
1001 = Route IN3P and IN3N to channel 1 inputs
1010 = Reserved
1011 = Reserved
1100 = Reserved
1101 = Reserved
1110 = Reserved
1111 = Reserved
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CH2SET: Channel 2 Settings
Address = 05h
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
PD2
GAIN2_2
GAIN2_1
GAIN2_0
MUX2_3
MUX2_2
MUX2_1
MUX2_0
The CH2SET Control Register configures the power mode, PGA gain, and multiplexer settings channels. See the
Input Multiplexer section for details.
Bit 7
PD2: Channel 2 power-down
0 = Normal operation (default)
1 = Channel 2 power-down
Bits[6:4]
GAIN2[2:0]: Channel 2 PGA gain setting
These bits determine the PGA gain setting for channel 2.
000 = 6 (default)
001 = 1
010 = 2
011 = 3
100 = 4
101 = 8
110 = 12
Bits[3:0]
MUX2[3:0]: Channel 2 input selection
These bits determine the channel 2 input selection.
0000 = Normal electrode input (default)
0001 = Input shorted (for offset measurements)
0010 = RLD_MEASURE
0011 = VDD/2 for supply measurement
0100 = Temperature sensor
0101 = Test signal
0110 = RLD_DRP (positive electrode is the driver)
0111 = RLD_DRM (negative electrode is the driver)
1000 = Reserved
1001 = Route IN3P and IN3N to channel 2 inputs
1010 = Reserved
1011 = Reserved
1100 = Reserved
1101 = Reserved
1110 = Reserved
1111 = Reserved
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RLD_SENS: Right Leg Drive Sense Selection
Address = 06h
BIT 7
0
BIT 6
0
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
PDB_RLD
RLD_LOFF_
SENS
RLD2N
RLD2P
RLD1N
RLD1P
This register controls the selection of the positive and negative signals from each channel for right leg drive
derivation. See the Right Leg Drive (RLD DC Bias Circuit) subsection of the ECG-Specific Functions section for
details.
Bits[7:6]
Must be set to '0'
Bit 5
PDB_RLD: RLD buffer power
This bit determines the RLD buffer power state.
0 = RLD buffer is powered down (default)
1 = RLD buffer is enabled
Bit 4
RLD_LOFF_SENSE: RLD lead-off sense function
This bit enables the RLD lead-off sense function.
0 = RLD lead-off sense is disabled (default)
1 = RLD lead-off sense is enabled
Bit 3
RLD2N: Channel 2 RLD negative inputs
This bit controls the selection of negative inputs from channel 2 for right leg drive derivation.
0 = Not connected (default)
1 = RLD connected to IN2N
Bit 2
RLD2P: Channel 2 RLD positive inputs
This bit controls the selection of positive inputs from channel 2 for right leg drive derivation.
0 = Not connected (default)
1 = RLD connected to IN2P
Bit 1
RLD1N: Channel 1 RLD negative inputs
This bit controls the selection of negative inputs from channel 1 for right leg drive derivation.
0 = Not connected (default)
1 = RLD connected to IN1N
Bit 0
RLD1P: Channel 1 RLD positive inputs
This bit controls the selection of positive inputs from channel 1 for right leg drive derivation.
0 = Not connected (default)
1 = RLD connected to IN1P
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LOFF_SENS: Lead-Off Sense Selection
Address = 07h
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
0
0
FLIP2
FLIP1
LOFF2N
LOFF2P
LOFF1N
LOFF1P
This register selects the positive and negative side from each channel for lead-off detection. See the Lead-Off
Detection subsection of the ECG-Specific Functions section for details. Note that the LOFF_STAT register bits
should be ignored if the corresponding LOFF_SENS bits are set to '1'.
Bits[7:6]
Must be set to '0'
Bit 5
FLIP2: Current direction selection
This bit controls the direction of the current used for lead-off derivation for channel 2.
0 = Disabled (default)
1 = Enabled
Bit 4
FLIP1: Current direction selection
This bit controls the direction of the current used for lead-off derivation for channel 1.
0 = Disabled (default)
1 = Enabled
Bit 3
LOFF2N: Channel 2 lead-off detection negative inputs
This bit controls the selection of negative input from channel 2 for lead-off detection.
0 = Disabled (default)
1 = Enabled
Bit 2
LOFF2P: Channel 2 lead-off detection positive inputs
This bit controls the selection of positive input from channel 2 for lead-off detection.
0 = Disabled (default)
1 = Enabled
Bit 1
LOFF1N: Channel 1 lead-off detection negative inputs
This bit controls the selection of negative input from channel 1 for lead-off detection.
0 = Disabled (default)
1 = Enabled
Bit 0
LOFF1P: Channel 1 lead-off detection positive inputs
This bit controls the selection of positive input from channel 1 for lead-off detection.
0 = Disabled (default)
1 = Enabled
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LOFF_STAT: Lead-Off Status
Address = 08h
BIT 7
0
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
0
RLD_STAT
(read only)
IN2N_OFF
(read only)
IN2P_OFF
(read only)
IN1N_OFF
(read only)
IN1P_OFF
(read only)
CLK_DIV
This register stores the status of whether the positive or negative electrode on each channel is on or off. See the
Lead-Off Detection subsection of the ECG-Specific Functions section for details. Ignore the LOFF_STAT values
if the corresponding LOFF_SENS bits are not set to '1'.
'0' is lead-on (default) and '1' is lead-off. When the LOFF_SENS bits[3:0] are '0', the LOFF_STAT bits should be
ignored.
Bit 7
Must be set to '0'
Bit 6
CLK_DIV: Clock divider selection
This bit sets the divider ratio between fCLK and fMOD. Two external clock values are supported: 512 kHz and 2.048 MHz.
This bit must be set so that fMOD = 128 kHz.
0 = fMOD/4 (default, when fCLK = 512 kHz)
1 = fMOD/16 (when fCLK = 2.048 MHz)
Bit 5
Must be set to '0'
Bit 4
RLD_STAT: RLD lead-off status
This bit determines the status of RLD.
0 = RLD is connected (default)
1 = RLD is not connected
Bit 3
IN2N_OFF: Channel 2 negative electrode status
This bit determines if the channel 2 negative electrode is connected or not.
0 = Connected (default)
1 = Not connected
Bit 2
IN2P_OFF: Channel 2 positive electrode status
This bit determines if the channel 2 positive electrode is connected or not.
0 = Connected (default)
1 = Not connected
Bit 1
IN1N_OFF: Channel 1 negative electrode status
This bit determines if the channel 1 negative electrode is connected or not.
0 = Connected (default)
1 = Not connected
Bit 0
IN1P_OFF: Channel 1 positive electrode status
This bit determines if the channel 1 positive electrode is connected or not.
0 = Connected (default)
1 = Not connected
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MISC1: Miscellaneous Control Register 1
Address = 09h
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
0
0
0
0
0
0
1
0
This register controls the miscellaneous functionality. For the ADS1191 and ADS1192 devices, 02h must be
written to the MISC1 register.
Bits[7:2]
Must be set to '0'
Bit 6
Must be set to '1'
Bit 0
Must be set to '0'
MISC2: Miscellaneous Control Register 2
Address = 0Ah
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
CALIB_ON
0
0
0
0
0
RLDREF_INT
0
This register controls the calibration functionality.
Bit 7
CALIB_ON: Calibration on
This bit is used to enable offset calibration.
0 = Off (default)
1 = On
Bits[6:2]
Must be '0'
Bit 1
RLDREF_INT: RLDREF signal
This bit determines the RLDREF signal source.
0 = RLDREF is external (default)
1 = RLDREF is fed internally
Bit 0
Must be set to '0'
GPIO: General-Purpose I/O Register
Address = 0Bh
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
0
0
0
0
GPIOC2
GPIOC1
GPIOD2
GPIOD1
This register controls the GPIO pins.
Bits[7:4]
Must be '0'
Bits[3:2]
GPIOC[2:1]: GPIO 1 and 2 control
These bits determine if the corresponding GPIOD pin is an input or output.
0 = Output
1 = Input (default)
Bits[1:0]
GPIOD[2:1]: GPIO 1 and 2 data
These bits are used to read and write data to the GPIO ports.
When reading the register, the data returned correspond to the state of the GPIO external pins, whether they are
programmed as inputs or as outputs. As outputs, a write to the GPIOD sets the output value. As inputs, a write to the
GPIOD has no effect.
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ADS1192
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ECG-SPECIFIC FUNCTIONS
INPUT MULTIPLEXER (REROUTING THE RIGHT LEG DRIVE SIGNAL)
The input multiplexer has ECG-specific functions for the right leg drive signal. The RLD signal is available at the
RLDOUT pin once the appropriate channels are selected for the RLD derivation, feedback elements are installed
external to the chip, and the loop is closed. This signal can be fed after filtering or fed directly into the RLDIN pin
as shown in Figure 42. This RLDIN signal can be multiplexed into any one of the input electrodes by setting the
MUX bits of the appropriate channel set registers to '0110' for P-side or '0111' for N-side. Figure 42 shows the
RLD signal generated from channel 1 and routed to the N-side of channel 2. This feature can be used to
dynamically change the electrode that is used as the reference signal to drive the patient body. Note that the
corresponding channel cannot be used and can be powered down.
RLD1P = 1
IN1P
EMI
Filter
PGA1
RLD1N = 1
MUX1[3:0] = 0000
IN1N
RLD2P = 0
IN2P
EMI
Filter
PGA2
RLD2N = 0
MUX1[3:0] = 0111
IN2N
RLDREF_INT = 1
(AVDD + AVSS)
MUX
2
RLDREF_INT = 0
RLD_AMP
Device
RLDIN/RLDREF
RLDOUT
1M
Filter or
Feedthrough
RLDINV
(1)
1.5 nF(1)
(1) Typical values for example only.
Figure 42. Example of RLDOUT Signal Configured to be Routed to IN2N
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SBAS566A – DECEMBER 2011 – REVISED SEPTEMBER 2012
Input Multiplexer (Measuring the Right Leg Drive Signal)
Also, the RLDOUT signal can be routed to a channel (that is not used for the calculation of RLD) for
measurement. Figure 43 shows the register settings to route the RLDIN signal to channel 2. The measurement is
done with respect to the voltage on the RLDREF pin. If RLDREF is chosen to be internal, it would be at (AVDD +
AVSS)/2. This feature is useful for debugging purposes during product development.
RLD1P = 1
IN1P
EMI
Filter
PGA1
RLD1N = 1
MUX1[3:0] = 0000
IN1N
RLD2P = 0
IN2P
EMI
Filter
RLD2N = 0
PGA2
MUX1[3:0] = 0010
IN2N
RLDREF_INT = 1
(AVDD + AVSS)
2
MUX
MUX1[3:0] = 0010
RLDREF_INT = 0
RLD_AMP
Device
RLDIN/RLDREF
RLDOUT
Filter or
Feedthrough
1M
RLDINV
(1)
1.5 nF(1)
(1) Typical values for example only.
Figure 43. RLDOUT Signal Configured to be Read Back by Channel 2
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ADS1192
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LEAD-OFF DETECTION
Patient electrode impedances are known to decay over time. It is necessary to continuously monitor these
electrode connections to verify a suitable connection is present. The ADS1191/2 lead-off detection functional
block provides significant flexibility to the user to choose from various lead-off detection strategies. Though called
lead-off detection, this is in fact an electrode-off detection.
The basic principle is to inject an excitation signal and measure the response to find out if the electrode is off. As
shown in the lead-off detection functional block diagram in Figure 44, this circuit provides two different methods
of determining the state of the patient electrode. The methods differ in the frequency content of the excitation
signal. Lead-off can be selectively done on a per channel basis using the LOFF_SENS register. Also, the internal
excitation circuitry can be disabled and just the sensing circuitry can be enabled.
Patient
Skin,
Electrode Contact
Model
Patient
Protection
Resistor
47 nF
51 k
IN1P_OFF/
IN2P_OFF
30 k
VINP
51 k
30 k
EMI
Filter
LOFF1P/
LOFF2P
47 nF
47 nF
51 k
VINN
PGA
LOFF1N/
LOFF2N
AVDD
To ADC
IN1N_OFF/
IN2N_OFF
4-Bit
DAC
AVSS
COMP_TH[2:0]
30 k
RLD OUT
NOTE: The RP value must be selected in order to be below the maximum allowable current flow into a patient (in accordance with the
relevant specification the latest revision of IEC 60601).
Figure 44. Lead-Off Detection
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DC Lead-Off
In this method, the lead-off excitation is with a dc signal. The dc excitation signal can be chosen from either an
external pull-up/pull-down resistor or a current source/sink, as shown in Figure 45. One side of the channel is
pulled to supply and the other side is pulled to ground. The internal current source and current sink can be
swapped by setting thebits in the LOFF_FLIP register. In case of current source/sink, the magnitude of the
current can be set by using the ILEAD_OFF[1:0] bits in the LOFF register. The current source/sink gives larger
input impedance compared to the 10-MΩ pull-up/pull-down resistor.
AVDD
AVDD
Device
Device
10 MW
INP
INP
PGA
INN
PGA
INN
10 MW
a) External Pull-Up/Pull-Down Resistors
b) Input Current Source
Figure 45. DC Lead-Off Excitation Options
Sensing of the response can be done either by looking at the digital output code from the device or by monitoring
the input voltages with an on-chip comparator. If either of the electrodes is off, the pull-up resistors and/or the
pull-down resistors saturate the channel. By looking at the output code it can be determined that either the P-side
or the N-side is off. To pinpoint which one is off, the comparators must be used. The input voltage is also
monitored using a comparator and a 4-bit digital-to-analog converter (DAC) whose levels are set by the
COMP_TH[2:0] bits in the LOFF register. The output of the comparators are stored in the LOFF_STAT register.
These two registers are available as a part of the output data stream. (See the Data Output Protocol (DOUT)
subsection of the SPI Interface section.) If dc lead-off is not used, the lead-off comparators can be powered
down by setting the PD_LOFF_COMP bit in the CONFIG2 register.
An example procedure to turn on dc lead-off is given in the Lead-Off subsection of the Quick-Start Guide section.
AC Lead-Off
In this method, an out-of-band ac signal is used for excitation. The ac signal is generated by alternatively
providing an internal current source and current sink at the input with a fixed frequency. The excitation frequency
is a function of the output data rate and is fDR/4. This out-of-band excitation signal is passed through the channel
and measured at the output.
Sensing of the ac signal is done by passing the signal through the channel to digitize it and measure at the
output. The ac excitation signals are introduced at a frequency that is above the band of interest, generating an
out-of-band differential signal that can be filtered out separately and processed. By measuring the magnitude of
the excitation signal at the output spectrum, the lead-off status can be calculated. Therefore, the ac lead-off
detection can be accomplished simultaneously with the ECG signal acquisition.
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ADS1192
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RLD Lead-Off
The ADS1191/2 provide two modes for determining whether the RLD is correctly connected:
• RLD lead-off detection during normal operation
• RLD lead-off detection during power-up
The following sections provide details of the two modes of operation.
RLD Lead-Off Detection During Normal Operation
During normal operation, the ADS1191/2 RLD lead-off at power-up function cannot be used because it is
necessary to power off the RLD amplifier.
RLD Lead-Off Detection At Power-Up
This feature is included in the ADS1191/2 for use in determining whether the right leg electrode is suitably
connected. At power-up, the ADS1191/2 provides a procedure to determine the RLD electrode connection status
using a current sink, as shown in Figure 46. The reference level of the comparator is set to determine the
acceptable RLD impedance threshold.
Patient
Skin,
Electrode Contact
Model
Patient
Protection
Resistor
To ADC input (through VREF
connection to any of the channels).
47 nF
51 k
RLD_STAT
30 k
RLD_LOFF_SENS
AVSS
NOTE: The RP value must be selected in order to be below the maximum allowable current flow into a patient (in accordance with the
relevant specification the latest revision of IEC 60601).
Figure 46. RLD Lead-Off Detection at Power-Up
When the RLD amplifier is powered on, the current source has no function. Only the comparator can be used to
sense the voltage at the output of the RLD amplifier. The comparator thresholds are set by the same LOFF[7:5]
bits used to set the thresholds for other negative inputs.
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SBAS566A – DECEMBER 2011 – REVISED SEPTEMBER 2012
Right Leg Drive (RLD DC Bias Circuit)
The right leg drive (RLD) circuitry is used as a means to counter the common-mode interference in an ECG
system as a result of power lines and other sources, including fluorescent lights. The RLD circuit senses the
common-mode of a selected set of electrodes and creates a negative feedback loop by driving the body with an
inverted common-mode signal. The negative feedback loop restricts the common-mode movement to a narrow
range, depending on the loop gain. Stabilizing the entire loop is specific to the individual user system based on
the various poles in the loop. The ADS1191/2 integrates the muxes to select the channel and an operational
amplifier. All the amplifier terminals are available at the pins, allowing the user to choose the components for the
feedback loop. The circuit shown in Figure 47 shows the overall functional connectivity for the RLD bias circuit.
From
MUX1P
RLD1P
400 k
PGA1P
150 k
RLD2P
400 k
PGA2P
60 k
150 k
From
MUX1N
From
MUX2P
150 k
60 k
400 k
PGA1N
RLD1N
150 k
400 k
PGA2N
From
MUX2N
RLD2N
RLDINV
(1)
CEXT
1.5 nF
(1)
REXT
1M
RLD
Amp
RLDOUT
(AVDD + AVSS)
RLDREF_INT
RLDIN/RLDREF
2
RLDREF_INT
To MUX
(1) Typical values.
Figure 47. RLD Channel Selection
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The reference voltage for the right leg drive can be chosen to be internally generated (AVDD + AVSS)/2 or it can
be provided externally with a resistive divider. The selection of an internal versus external reference voltage for
the RLD loop is defined by writing the appropriate value to the RLDREF_INT bit in the MISC2 register.
If the RLD function is not used, the amplifier can be powered down using the PDB_RLD bit. This bit is also used
in daisy-chain mode to power-down all but one of the RLD amplifiers.
The functionality of the RLDIN pin is explained in the Input Multiplexer section. An example procedure to use the
RLD amplifier is shown in the Right Leg Drive subsection of the Quick-Start Guide section.
RLD Configuration with Multiple Devices
RLDIN/
RLDREF
RLD
OUT
Power-Down
Device N
VA1
VA2
RLDINV
(AVDD+AVSS)
2
RLDIN/
RLDREF
RLD
OUT
Device 2
VA1
VA2
To Input MUX
(AVDD+AVSS)
2
To Input MUX
To Input MUX
Figure 48 shows multiple devices connected to an RLD.
RLDIN/
RLDREF
RLDINV
(AVDD+AVSS)
2
Device 1
VA1
RLD
OUT
REXT
VA2
RLDINV
CEXT
Figure 48. RLD Connection for Multiple Devices
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SBAS566A – DECEMBER 2011 – REVISED SEPTEMBER 2012
QUICK-START GUIDE
PCB LAYOUT
Power Supplies and Grounding
The ADS1191/2 have two supplies: AVDD and DVDD. AVDD should be as quiet as possible. AVDD provides the
supply to the charge pump block and has transients at fCLK. It is important to eliminate noise from AVDD that is
non-synchronous with the ADS1191/2 operation. Each supply of the ADS1191/2 should be bypassed with 10-μF
and a 0.1-μF solid ceramic capacitors. It is recommended that placement of the digital circuits (DSP,
microcontrollers, FPGAs, etc.) in the system is done such that the return currents on those devices do not cross
the analog return path of the ADS1191/2. The ADS1191/2 can be powered from unipolar or bipolar supplies.
The capacitors used for decoupling can be of the surface-mount, low-cost, low-profile multi-layer ceramic type. In
most cases the VCAP1 capacitor can also be a multi-layer ceramic, but in systems where the board is subjected
to high or low frequency vibration, it is recommend that a non-ferroelectric capacitor such as a tantalum or class
1 capacitor (for example, C0G or NPO) be installed. EIA class 2 and class 3 dielectrics (such as X7R, X5R, X8R,
etc.) are ferroelectric. The piezoelectric property of these capacitors can appear as electrical noise coming from
the capacitor. When using internal reference, noise on the VCAP1 node results in performance degradation.
Connecting the Device to Unipolar (+3 V/+1.8 V) Supplies
Figure 49 illustrates the ADS1191/2 connected to a unipolar supply. In this example, the analog supply (AVDD) is
referenced to analog ground (AVSS) and the digital supply (DVDD) is referenced to digital ground (DGND).
+1.8 V
+3 V
0.1 mF
1 mF
1 mF
0.1 mF
DVDD
AVDD
VREFP
VREFN
0.1 mF
10 mF
PGA1N
4.7 nF
VCAP1
PGA1P
VCAP2
Device
PGA2N
4.7 nF
PGA2P
AVSS
DGND
1 mF
1 mF
NOTE: Place the capacitors for supply, reference, VCAP1, and VCAP2 as close to the package as possible.
Figure 49. Single-Supply Operation
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Connecting the Device to Bipolar (±1.5 V/1.8 V) Supplies
Figure 50 illustrates the ADS1191/2 connected to a bipolar supply. In this example, the analog supplies connect
to the device analog supply (AVDD). This supply is referenced to the device analog return (AVSS), and the
digital supply (DVDD) is referenced to the device digital ground return (DGND).
+1.5 V
+1.8 V
1 mF
0.1 mF
0.1 mF
1 mF
DVDD
AVDD
VREFP
VREFN
0.1 mF
10 mF
PGA1N
4.7 nF
-1.5 V
PGA1P
VCAP1
Device
VCAP2
PGA2N
4.7 nF
PGA2P
AVSS
DGND
1 mF
1 mF
1 mF
0.1 mF
-1.5 V
NOTE: Place the capacitors for supply, reference, VCAP1, and VCAP2 as close to the package as possible.
Figure 50. Bipolar Supply Operation
Shielding Analog Signal Paths
As with any precision circuit, careful PCB layout ensures the best performance. It is essential to make short,
direct interconnections and avoid stray wiring capacitance—particularly at the analog input pins and AVSS.
These analog input pins are high-impedance and extremely sensitive to extraneous noise. The AVSS pin should
be treated as a sensitive analog signal and connected directly to the supply ground with proper shielding.
Leakage currents between the PCB traces can exceed the input bias current of the ADS1191/2 if shielding is not
implemented. Digital signals should be kept as far as possible from the analog input signals on the PCB.
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SBAS566A – DECEMBER 2011 – REVISED SEPTEMBER 2012
POWER-UP SEQUENCING
Before device power-up, all digital and analog inputs must be low. At the time of power-up, all of these signals
should remain low until the power supplies have stabilized, as shown in Figure 51. At this time, begin supplying
the master clock signal to the CLK pin. Wait for time tPOR, then transmit a RESET pulse. After releasing RESET,
the configuration register must be programmed, see the CONFIG1: Configuration Register 1 subsection of the
Register Map section for details. The power-up sequence timing is shown in Table 9.
tPOR
Power Supplies
tRST
RESET
18 tCLK
Start Using the Device
Figure 51. Power-Up Timing Diagram
Table 9. Power-Up Sequence Timing
SYMBOL
DESCRIPTION
MIN
tPOR
Wait after power-up until reset
211
TYP
MAX
UNIT
tMOD
tRST
Reset low width
1
tMOD
SETTING THE DEVICE FOR BASIC DATA CAPTURE
The following section outlines the procedure to configure the device in a basic state and capture data. This
procedure is intended to put the device in a data sheet condition to check if the device is working properly in the
user's system. It is recommended that this procedure be followed initially to get familiar with the device settings.
Once this procedure has been verified, the device can be configured as needed. For details on the timings for
commands refer to the appropriate sections in the data sheet. Also, some sample programming codes are added
for the ECG-specific functions.
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Analog/Digital Power-Up
Set CLKSEL Pin = 0 and
Provide External Clock
fCLK = 512 kHz
Yes
// Follow Power-Up Sequencing
External
Clock
No
Set CLKSEL Pin = 1
and Wait for Oscillator
to Wake Up
// If START is Tied High, After This Step
// DRDY Toggles at fMOD/256
Set PWDN/RESET = 1
Wait for 1 s for
Power-On Reset
// Delay for Power-On Reset and Oscillator Start-Up
Issue Reset Pulse,
Wait for 18 tCLKs
Set PDB_REFBUF = 1
and Wait for Internal
Reference To Settle
// Activate DUT
//CS can be Either Tied Permanently Low
// Or Selectively Pulled Low Before Sending
// Commands or Reading/Sending Data From/To Device
Send SDATAC
Command
// Device Wakes Up in RDATAC Mode, so Send
// SDATAC Command so Registers can be Written
SDATAC
External Reference
// If Using Internal Reference, Send This Command
-- WREG CONFIG2 A0h
No
Yes
Write Certain Registers,
Including Input Short
// DRATE = 500 SPS
WREG CONFIG1 02h
// Set All Channels to Input Short
WREG CHnSET 01h
Set START = 1
// Activate Conversion
// After This Point DRDY Should Toggle at
// fCLK/256
RDATAC
// Put the Device Back in RDATAC Mode
RDATAC
Capture Data and
Check Noise
Set Test Signals
Capture Data and
Test Signals
// Look for DRDY and Issue 16 + 2
16 SCLKs
// Activate a (1 mV VREF/2.4) Square-Wave Test Signal
// On All Channels
SDATAC
WREG CONFIG2 A3h
WREG CHnSET 05h
RDATAC
// Look for DRDY and Issue 16 + 2
16 SCLKs
Figure 52. Initial Flow at Power-Up
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SBAS566A – DECEMBER 2011 – REVISED SEPTEMBER 2012
Lead-Off
Sample code to set dc lead-off with current source/sink resistors on all channels
WREG LOFF 10h // Comparator threshold at 95% and 5%, current source/sink resistor // DC lead-off
WREG CONFIG2 E0h // Turn-on dc lead-off comparators
WREG LOFF_SENS 0Fh // Turn on both P- and Nside of all channels for lead-off sensing
Observe the status bits of the output data stream to monitor lead-off status.
Right Leg Drive
Sample code to choose RLD as an average of the first three channels.
WREG RLD_SENSP 07h // Select channel 1—3 P-side for RLD sensing
WREG RLD_SENSN 07h // Select channel 1—3 N-side for RLD sensing
WREG CONFIG3 b’x1xx 1100 // Turn on RLD amplifier, set internal RLDREF voltage
Sample code to route the RLD_OUT signal through channel 4 N-side and measure RLD with channel 5. Make
sure the external side to the chip RLDOUT is connected to RLDIN.
WREG CONFIG3 b’xxx1 1100 // Turn on RLD amplifier, set internal RLDREF voltage, set RLD measurement bit
WREG CH4SET b’1xxx 0111 // Route RLDIN to channel 4 N-side
WREG CH5SET b’1xxx 0010 // Route RLDIN to be measured at channel 5 w.r.t RLDREF
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REVISION HISTORY
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Original (December 2011) to Revision A
Page
•
Added RSM data to Family and Ordering Information table ................................................................................................. 2
•
Changed AVSS to DGND row in Absolute Maximum Ratings table .................................................................................... 2
•
Changed Channel Performance (AC performance), SNR typical specification in Electrical Characteristics table .............. 3
•
Changed Supply Current parameters in Electrical Characteristics table .............................................................................. 5
•
Changed ADS1192/2R to ADS1192 in 3 V Power Dissipation, Quiescent power dissipation parameter of Electrical
Characteristics table ............................................................................................................................................................. 6
•
Added RSM pinout package ................................................................................................................................................. 9
•
Changed fCLK to fMOD in bit 6 description of LOFF_STAT: Lead-Off Status register ........................................................... 44
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PACKAGE OPTION ADDENDUM
www.ti.com
24-Sep-2012
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package
Drawing
Pins
Package Qty
Eco Plan
(2)
Lead/
Ball Finish
MSL Peak Temp
(3)
ADS1191IPBS
ACTIVE
TQFP
PBS
32
250
Green (RoHS
& no Sb/Br)
CU NIPDAU Level-2-260C-1 YEAR
ADS1191IPBSR
ACTIVE
TQFP
PBS
32
1000
Green (RoHS
& no Sb/Br)
CU NIPDAU Level-2-260C-1 YEAR
ADS1191IRSMR
ACTIVE
VQFN
RSM
32
3000
Green (RoHS
& no Sb/Br)
CU NIPDAU Level-2-260C-1 YEAR
ADS1191IRSMT
ACTIVE
VQFN
RSM
32
250
Green (RoHS
& no Sb/Br)
CU NIPDAU Level-2-260C-1 YEAR
ADS1192IPBS
ACTIVE
TQFP
PBS
32
250
Green (RoHS
& no Sb/Br)
CU NIPDAU Level-2-260C-1 YEAR
ADS1192IPBSR
ACTIVE
TQFP
PBS
32
1000
Green (RoHS
& no Sb/Br)
CU NIPDAU Level-2-260C-1 YEAR
ADS1192IRSMR
ACTIVE
VQFN
RSM
32
3000
Green (RoHS
& no Sb/Br)
CU NIPDAU Level-2-260C-1 YEAR
ADS1192IRSMT
ACTIVE
VQFN
RSM
32
250
Green (RoHS
& no Sb/Br)
CU NIPDAU Level-2-260C-1 YEAR
Samples
(Requires Login)
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(3)
MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
Addendum-Page 1
PACKAGE OPTION ADDENDUM
www.ti.com
24-Sep-2012
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Addendum-Page 2
PACKAGE MATERIALS INFORMATION
www.ti.com
22-Sep-2012
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
Package Package Pins
Type Drawing
SPQ
Reel
Reel
A0
Diameter Width (mm)
(mm) W1 (mm)
B0
(mm)
K0
(mm)
P1
(mm)
W
Pin1
(mm) Quadrant
ADS1191IPBSR
TQFP
PBS
32
1000
330.0
16.4
7.2
7.2
1.5
12.0
16.0
Q2
ADS1191IRSMR
VQFN
RSM
32
3000
330.0
12.4
4.25
4.25
1.15
8.0
12.0
Q2
ADS1191IRSMT
VQFN
RSM
32
250
180.0
12.4
4.25
4.25
1.15
8.0
12.0
Q2
ADS1192IPBSR
TQFP
PBS
32
1000
330.0
16.4
7.2
7.2
1.5
12.0
16.0
Q2
ADS1192IRSMR
VQFN
RSM
32
3000
330.0
12.4
4.25
4.25
1.15
8.0
12.0
Q2
ADS1192IRSMT
VQFN
RSM
32
250
180.0
12.4
4.25
4.25
1.15
8.0
12.0
Q2
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
22-Sep-2012
*All dimensions are nominal
Device
Package Type
Package Drawing
Pins
SPQ
Length (mm)
Width (mm)
Height (mm)
ADS1191IPBSR
TQFP
PBS
32
1000
367.0
367.0
38.0
ADS1191IRSMR
VQFN
RSM
32
3000
367.0
367.0
35.0
ADS1191IRSMT
VQFN
RSM
32
250
210.0
185.0
35.0
ADS1192IPBSR
TQFP
PBS
32
1000
367.0
367.0
38.0
ADS1192IRSMR
VQFN
RSM
32
3000
367.0
367.0
35.0
ADS1192IRSMT
VQFN
RSM
32
250
210.0
185.0
35.0
Pack Materials-Page 2
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