AD AD7192BRUZ 4.8 khz, ultralow noise, 24-bit sigma-delta adc with pga Datasheet

4.8 kHz, Ultralow Noise, 24-Bit
Sigma-Delta ADC with PGA
AD7192
FEATURES
Temperature measurement
Chromatography
PLC/DCS analog input modules
Data acquisition
Medical and scientific instrumentation
RMS noise: 11 nV @ 4.7 Hz (gain = 128)
15.5 noise-free bits @ 2.4 kHz (gain = 128)
Up to 22 noise-free bits (gain = 1)
Offset drift: 5 nV/°C
Gain drift: 1 ppm/°C
Specified drift over time
2 differential/4 pseudo differential input channels
Automatic channel sequencer
Programmable gain (1 to 128)
Output data rate: 4.7 Hz to 4.8 kHz
Internal or external clock
Simultaneous 50 Hz/60 Hz rejection
4 general-purpose digital outputs
Power supply
AVDD: 3 V to 5.25 V
DVDD: 2.7 V to 5.25 V
Current: 4.35 mA
Temperature range: –40°C to +105°C
Package: 24-lead TSSOP
GENERAL DESCRIPTION
The AD7192 is a low noise, complete analog front end for high
precision measurement applications. It contains a low noise,
24-bit sigma-delta (Σ-Δ) analog-to-digital converter (ADC).
The on-chip low noise gain stage means that signals of small
amplitude can be interfaced directly to the ADC.
The device can be configured to have two differential inputs or
four pseudo differential inputs. The on-chip channel sequencer
allows several channels to be enabled, and the AD7192 sequentially
converts on each enabled channel. This simplifies communication
with the part. The on-chip 4.92 MHz clock can be used as the
clock source to the ADC or, alternatively, an external clock or
crystal can be used. The output data rate from the part can be
varied from 4.7 Hz to 4.8 kHz.
The device has two digital filter options. The choice of filter
affects the rms noise/noise-free resolution at the programmed
output data rate, the settling time, and the 50 Hz/60 Hz
rejection. For applications that require all conversions to be
settled, the AD7192 includes a zero latency feature.
INTERFACE
3-wire serial
SPI, QSPI™, MICROWIRE™, and DSP compatible
Schmitt trigger on SCLK
APPLICATIONS
The part operates with a power supply from 3 V to 5.25 V. It
consumes a current of 4.35 mA. It is housed in a 24-lead TSSOP
package.
Weigh scales
Strain gage transducers
Pressure measurement
FUNCTIONAL BLOCK DIAGRAM
AGND
AIN1
AIN2
AIN3
AIN4
AINCOM
AVDD
AVDD
MUX
DVDD DGND REFIN1(+) REFIN1(–)
REFERENCE
DETECT
AD7192
Σ-Δ
ADC
PGA
SERIAL
INTERFACE
AND
CONTROL
LOGIC
DOUT/RDY
DIN
SCLK
CS
SYNC
AGND
TEMP
SENSOR
P3
P2
BPDSW
AGND
MCLK1 MCLK2
P0/REFIN2(–) P1/REFIN2(+)
07822-001
CLOCK
CIRCUITRY
Figure 1.
Rev. A
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rights of third parties that may result from its use. Specifications subject to change without notice. No
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www.analog.com
Fax: 781.461.3113
©2009 Analog Devices, Inc. All rights reserved.
AD7192
TABLE OF CONTENTS
Features .............................................................................................. 1
Offset Register ............................................................................ 24
Interface ............................................................................................. 1
Full-Scale Register ...................................................................... 24
Applications ....................................................................................... 1
ADC Circuit Information.............................................................. 25
General Description ......................................................................... 1
Overview ..................................................................................... 25
Functional Block Diagram .............................................................. 1
Filter, Output Data Rate, and Settling Time ........................... 25
Revision History ............................................................................... 2
Digital Interface .......................................................................... 28
Specifications..................................................................................... 3
Circuit Description......................................................................... 32
Timing Characteristics..................................................................... 7
Analog Input Channel ............................................................... 32
Circuit and Timing Diagrams..................................................... 7
Programmable Gain Array (PGA) ........................................... 32
Absolute Maximum Ratings............................................................ 9
Bipolar/Unipolar Configuration .............................................. 32
Thermal Resistance ...................................................................... 9
Data Output Coding .................................................................. 32
ESD Caution .................................................................................. 9
Clock ............................................................................................ 32
Pin Configuration and Function Descriptions ........................... 10
Burnout Currents ....................................................................... 33
Typical Performance Characteristics ........................................... 12
Reference ..................................................................................... 33
RMS Noise and Resolution............................................................ 14
Reference Detect ......................................................................... 33
4
Reset ............................................................................................. 34
3
System Synchronization ............................................................ 34
4
Temperature Sensor ................................................................... 34
3
Sinc Chop Enabled .................................................................... 17
Bridge Power-Down Switch ...................................................... 34
On-Chip Registers .......................................................................... 18
Logic Outputs ............................................................................. 34
Communications Register ......................................................... 18
Enable Parity ............................................................................... 35
Status Register ............................................................................. 19
Calibration................................................................................... 35
Mode Register ............................................................................. 19
Grounding and Layout .............................................................. 36
Configuration Register .............................................................. 21
Applications Information .............................................................. 37
Data Register ............................................................................... 23
Weigh Scales ................................................................................ 37
ID Register ................................................................................... 23
Outline Dimensions ....................................................................... 38
GPOCON Register ..................................................................... 24
Ordering Guide .......................................................................... 38
Sinc Chop Disabled ................................................................... 14
Sinc Chop Disabled ................................................................... 15
Sinc Chop Enabled .................................................................... 16
REVISION HISTORY
5/09—Rev. 0 to Rev. A
Change to Gain Error Specification ............................................... 3
Changes to Table 3 ............................................................................ 9
5/09—Revision 0: Initial Version
Rev. A | Page 2 of 40
AD7192
SPECIFICATIONS
AVDD = 3 V to 5.25 V, DVDD = 2.7 V to 5.25 V, AGND = DGND = 0 V; REFINx(+) = AVDD, REFINx(−) = AGND, MCLK = 4.92 MHz,
TA = TMIN to TMAX, unless otherwise noted.
Table 1.
Parameter
ADC
Output Data Rate
No Missing Codes2
Resolution
RMS Noise and Output Data Rates
Integral Nonlinearity
Gain = 12
Gain > 1
Offset Error4, 5
Offset Error Drift vs. Temperature
Offset Error Drift vs. Time
Gain Error4
Gain Drift vs. Temperature
Gain Drift vs. Time
Power Supply Rejection
Common-Mode Rejection
@ DC2
@ DC
@ 50 Hz, 60 Hz2
@ 50 Hz, 60 Hz2
Normal Mode Rejection2
Sinc4 Filter
Internal Clock
@ 50 Hz, 60 Hz
@ 50 Hz
@ 60 Hz
AD7192B
Unit
Test Conditions/Comments1
4.7 to 4800
1.17 to 1200
1.56 to 1600
24
24
Hz nom
Hz nom
Hz nom
Bits min
Bits min
Chop disabled
Chop enabled, sinc4 filter
Chop enabled, sinc3 filter
FS > 1, sinc4 filter3
FS > 4, sinc3 filter3
See the RMS Noise and Resolution section
See the RMS Noise and Resolution section
±10
±15
±30
±30
±150/gain
±0.5
±150/gain
±5
±5
25
±0.001
ppm of FSR max
ppm of FSR max
ppm of FSR max
ppm of FSR max
μV typ
μV typ
nV/°C typ
nV/°C typ
nV/°C typ
nV/1000 hours typ
% typ
−0.39
% typ
±0.003
% typ
±0.005
% typ
±2 ppm typical, AVDD = 5 V
±2 ppm typical, AVDD = 3 V
±5 ppm typical, AVDD = 5 V
±12 ppm typical, AVDD = 3 V
Chop disabled
Chop enabled
Gain = 1 to 16; chop disabled
Gain = 32 to 128; chop disabled
Chop enabled
Gain > 32
AVDD = 5 V, gain = 1, TA = 25°C (factory
calibration conditions)
Gain = 128, before full-scale calibration (see
Table 23)
Gain > 1, after internal full-scale calibration,
AVDD ≥ 4.75 V.
Gain > 1, after internal full-scale calibration,
AVDD < 4.75 V
±1
10
90
95
ppm/°C typ
ppm/1000 hours typ
dB typ
dB min
100
110
120
120
dB min
dB min
dB min
dB min
Gain = 1, VIN = 1 V.
Gain > 1, VIN = 1 V/gain.
10 Hz output data rate, 50 ± 1 Hz, 60 ± 1 Hz.
50 ± 1 Hz (50 Hz output data rate), 60 ± 1 Hz
(60 Hz output data rate).
100
74
dB min
dB min
96
97
dB min
dB min
10 Hz output data rate, 50 ± 1 Hz, 60 ± 1 Hz.
50 Hz output data rate, REJ606 = 1,
50 ± 1 Hz, 60 ± 1 Hz.
50 Hz output data rate, 50 ± 1 Hz.
60 Hz output data rate, 60 ± 1 Hz.
Rev. A | Page 3 of 40
Gain = 1.
Gain = 1, VIN = 1 V.
Gain > 1, VIN = 1 V/gain, 110 dB typ.
AD7192
Parameter
External Clock
@ 50 Hz, 60 Hz
@ 50 Hz
@ 60 Hz
3
Sinc Filter
Internal Clock
@ 50 Hz, 60 Hz
@ 50 Hz
@ 60 Hz
External Clock
@ 50 Hz, 60 Hz
@ 50 Hz
@ 60 Hz
ANALOG INPUTS
Differential Input Voltage Ranges
Absolute AIN Voltage Limits2
Unbuffered Mode
Buffered Mode
Analog Input Current
Buffered Mode
Input Current2
Input Current Drift
Unbuffered Mode
Input Current
Input Current Drift
REFERENCE INPUT
REFIN Voltage
Absolute REFIN Voltage Limits2
Average Reference Input Current
AD7192B
Unit
Test Conditions/Comments1
120
82
dB min
dB min
120
120
dB min
dB min
10 Hz output data rate, 50 ± 1 Hz, 60 ± 1 Hz.
50 Hz output data rate, REJ606 = 1,
50 ± 1 Hz, 60 ± 1 Hz.
50 Hz output data rate, 50 ± 1 Hz.
60 Hz output data rate, 60 ± 1 Hz.
75
60
dB min
dB min
70
70
dB min
dB min
100
67
dB min
dB min
95
95
dB min
dB min
± VREF/gain
V nom
± (AVDD – 1.25 V)/gain
V min/max
AGND − 50 mV
AVDD + 50 mV
AGND + 250 mV
AVDD − 250 mV
V min
V max
V min
V max
±2
±3
±5
nA max
nA max
pA/°C typ
Gain = 1.
Gain > 1.
±3.5
μA/V typ
±1
±0.05
±1.6
μA/V typ
nA/V/°C typ
nA/V/°C typ
Gain = 1, input current varies with input
voltage.
Gain > 1.
External clock.
Internal clock.
AVDD
1
AVDD
V nom
V min
V max
GND – 50 mV
AVDD + 50 mV
4.5
V min
V max
μA/V typ
Rev. A | Page 4 of 40
10 Hz output data rate, 50 ± 1 Hz, 60 ± 1 Hz.
50 Hz output data rate, REJ606 = 1,
50 ± 1 Hz, 60 ± 1 Hz.
50 Hz output data rate, 50 ± 1 Hz.
60 Hz output data rate, 60 ± 1 Hz.
10 Hz output data rate, 50 ± 1 Hz, 60 ± 1 Hz.
50 Hz output data rate, REJ606 = 1,
50 ± 1 Hz, 60 ± 1 Hz.
50 Hz output data rate, 50 ± 1 Hz.
60 Hz output data rate, 60 ± 1 Hz.
VREF = REFINx(+) − REFINx(−),
gain = 1 to 128.
Gain > 1.
REFIN = REFINx(+) − REFINx(−).
The differential input must be limited to
±(AVDD – 1.25 V)/gain when gain > 1.
AD7192
Parameter
Average Reference Input Current
Drift
Normal Mode Rejection2
Common-Mode Rejection
Reference Detect Levels
TEMPERATURE SENSOR
Accuracy
Sensitivity
BRIDGE POWER-DOWN SWITCH
RON
Allowable Current2
BURNOUT CURRENTS
AIN Current
DIGITAL OUTPUTS (P0 to P3)
Output High Voltage, VOH
Output Low Voltage, VOL
Output High Voltage, VOH
Output Low Voltage, VOL
Floating-State Leakage Current2
Floating-State Output
Capacitance
INTERNAL/EXTERNAL CLOCK
Internal Clock
Frequency
Duty Cycle
External Clock/Crystal
Frequency
Input Low Voltage VINL
Input High Voltage, VINH
Input Current
LOGIC INPUTS
Input High Voltage, VINH2
Input Low Voltage, VINL2
Hysteresis2
Input Currents
LOGIC OUTPUT (DOUT/RDY)
Output High Voltage, VOH2
Output Low Voltage, VOL2
Output High Voltage, VOH2
Output Low Voltage, VOL2
Floating-State Leakage Current
Floating-State Output
Capacitance
Data Output Coding
AD7192B
±0.03
Unit
nA/V/°C typ
Test Conditions/Comments 1
External clock.
±1.3
Same as for analog inputs
100
0.3
0.6
nA/V/°C typ
Internal clock.
±2
2815
°C typ
Codes/°C typ
Applies after user calibration at 25°C.
Bipolar mode.
10
30
Ω max
mA max
Continuous current.
500
nA nom
Analog inputs must be buffered and chop
disabled.
AVDD − 0.6
0.4
4
0.4
±100
10
V min
V max
V min
V max
nA max
pF typ
AVDD = 3 V, ISOURCE = 100 μA.
AVDD = 3 V, ISINK = 100 μA.
AVDD = 5 V, ISOURCE = 200 μA.
AVDD = 5 V, ISINK = 800 μA.
4.92 ± 4%
50:50
MHz min/max
% typ
4.9152
2.4576/5.12
0.8
0.4
2.5
3.5
±10
MHz nom
MHz min/max
V max
V max
V min
V min
μA max
2
0.8
0.1/0.25
±10
V min
V max
V min/V max
μA max
DVDD − 0.6
0.4
4
0.4
±10
10
V min
V max
V min
V max
μA max
pF typ
dB typ
V min
V max
Offset binary
Rev. A | Page 5 of 40
DVDD = 5 V.
DVDD = 3 V.
DVDD = 3 V.
DVDD = 5 V.
DVDD = 3 V, ISOURCE = 100 μA.
DVDD = 3 V, ISINK = 100 μA.
DVDD = 5 V, ISOURCE = 200 μA.
DVDD = 5 V, ISINK = 1.6 mA.
AD7192
Parameter
SYSTEM CALIBRATION2
Full-Scale Calibration Limit
Zero-Scale Calibration Limit
Input Span
POWER REQUIREMENTS 7
Power Supply Voltage
AVDD − AGND
DVDD − DGND
Power Supply Currents
AIDD Current
DIDD Current
IDD (Power-Down Mode)
AD7192B
Unit
1.05 × FS
−1.05 × FS
0.8 × FS
2.1 × FS
V max
V min
V min
V max
3/5.25
2.7/5.25
V min/max
V min/max
0.6
0.85
3.2
3.6
4.5
5
0.4
0.6
1.5
3
mA max
mA max
mA max
mA max
mA max
mA max
mA max
mA max
mA typ
μA max
1
Test Conditions/Comments 1
0.53 mA typical, gain = 1, buffer off.
0.75 mA typical, gain = 1, buffer on.
2.5 mA typical, gain = 8, buffer off.
3 mA typical, gain = 8, buffer on.
3.5 mA typical, gain = 16 to 128, buffer off.
4 mA typical, gain = 16 to 128, buffer on.
0.35 mA typical, DVDD = 3 V.
0.5 mA typical, DVDD = 5 V.
External crystal used.
Temperature range: −40°C to +105°C.
Specification is not production tested but is supported by characterization data at initial product release.
3
FS is the decimal equivalent of Bit FS9 to Bit FS0 in the mode register.
4
Following a system or internal zero-scale calibration, the offset error is in the order of the noise for the programmed gain and output data rate selected. A system fullscale calibration reduces the gain error to the order of the noise for the programmed gain and output data rate.
5
The analog inputs are configured for differential mode.
6
REJ60 is a bit in the mode register. When the output data rate is set to 50 Hz, setting REJ60 to 1 places a notch at 60 Hz, allowing simultaneous 50 Hz/60 Hz rejection.
7
Digital inputs equal to DVDD or DGND.
2
Rev. A | Page 6 of 40
AD7192
TIMING CHARACTERISTICS
AVDD = 3 V to 5.25 V, DVDD = 2.7 V to 5.25 V, AGND = DGND = 0 V, Input Logic 0 = 0 V, Input Logic 1 = DVDD, unless otherwise noted.
Table 2.
Parameter
t3
t4
READ OPERATION
t1
t2 3
t5 5, 6
t6
t7
WRITE OPERATION
t8
t9
t10
t11
Limit at TMIN, TMAX (B Version)
100
100
Unit
ns min
ns min
Conditions/Comments 1, 2
SCLK high pulse width
SCLK low pulse width
0
60
80
0
60
80
10
80
0
10
ns min
ns max
ns max
ns min
ns max
ns max
ns min
ns max
ns min
ns min
CS falling edge to DOUT/RDY active time
DVDD = 4.75 V to 5.25 V
DVDD = 2.7 V to 3.6 V
SCLK active edge to data valid delay 4
DVDD = 4.75 V to 5.25 V
DVDD = 2.7 V to 3.6 V
Bus relinquish time after CS inactive edge
0
30
25
0
ns min
ns min
ns min
ns min
CS falling edge to SCLK active edge setup time4
Data valid to SCLK edge setup time
Data valid to SCLK edge hold time
CS rising edge to SCLK edge hold time
SCLK inactive edge to CS inactive edge
SCLK inactive edge to DOUT/RDY high
1
Sample tested during initial release to ensure compliance. All input signals are specified with tR = tF = 5 ns (10% to 90% of DVDD) and timed from a voltage level of 1.6 V.
See Figure 3 and Figure 4.
3
These numbers are measured with the load circuit shown in Figure 2 and defined as the time required for the output to cross the VOL or VOH limits.
4
The SCLK active edge is the falling edge of SCLK.
5
These numbers are derived from the measured time taken by the data output to change 0.5 V when loaded with the circuit shown in Figure 2. The measured number
is then extrapolated back to remove the effects of charging or discharging the 50 pF capacitor. This means that the times quoted in the timing characteristics are the
true bus relinquish times of the part and, as such, are independent of external bus loading capacitances.
6 RDY
returns high after a read of the data register. In single conversion mode and continuous conversion mode, the same data can be read again, if required, while RDY
is high, although care should be taken to ensure that subsequent reads do not occur close to the next output update. If the continuous read feature is enabled, the
digital word can be read only once.
2
CIRCUIT AND TIMING DIAGRAMS
ISINK (1.6mA WITH DVDD = 5V,
100µA WITH DVDD = 3V)
TO
OUTPUT
PIN
1.6V
ISOURCE (200µA WITH DVDD = 5V,
100µA WITH DVDD = 3V)
Figure 2. Load Circuit for Timing Characterization
Rev. A | Page 7 of 40
07822-002
50pF
AD7192
CS (I)
t6
t1
t5
MSB
DOUT/RDY (O)
LSB
t7
t2
t3
07822-003
SCLK (I)
t4
I = INPUT, O = OUTPUT
Figure 3. Read Cycle Timing Diagram
CS (I)
t11
t8
SCLK (I)
t9
t10
MSB
LSB
I = INPUT, O = OUTPUT
Figure 4. Write Cycle Timing Diagram
Rev. A | Page 8 of 40
07822-004
DIN (I)
AD7192
ABSOLUTE MAXIMUM RATINGS
TA = 25°C, unless otherwise noted.
THERMAL RESISTANCE
Table 3.
Parameter
AVDD to AGND
DVDD to AGND
AGND to DGND
Analog Input Voltage to AGND
Reference Input Voltage to AGND
Digital Input Voltage to DGND
Digital Output Voltage to DGND
AIN/Digital Input Current
Operating Temperature Range
Rating
−0.3 V to +6.5 V
−0.3 V to +6.5 V
−0.3 V to +0.3 V
−0.3 V to AVDD + 0.3 V
−0.3 V to AVDD + 0.3 V
−0.3 V to DVDD + 0.3 V
−0.3 V to DVDD + 0.3 V
10 mA
−40°C to +105°C
Storage Temperature Range
Maximum Junction Temperature
Lead Temperature, Soldering
Reflow
−65°C to +150°C
150°C
θJA is specified for the worst-case conditions, that is, a device
soldered in a circuit board for surface-mount packages.
Table 4. Thermal Resistance
Package Type
24-Lead TSSOP
ESD CAUTION
260°C
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
Rev. A | Page 9 of 40
θJA
128
θJC
42
Unit
°C/W
AD7192
MCLK1 1
24
DIN
MCLK2 2
23
DOUT/RDY
SCLK 3
22
SYNC
CS 4
AD7192
21
DVDD
P3 5
TOP VIEW
(Not to Scale)
20
AVDD
P2 6
19
DGND
P1/REFIN2(+) 7
18
AGND
P0/REFIN2(–) 8
17
BPDSW
NC 9
16
REFIN1(–)
AINCOM 10
15
REFIN1(+)
AIN1 11
14
AIN4
AIN2 12
13
AIN3
NC = NO CONNECT
07822-005
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
Figure 5. Pin Configuration
Table 5. Pin Function Descriptions
Pin No.
1
Mnemonic
MCLK1
2
MCLK2
3
SCLK
4
CS
5
6
7
P3
P2
P1/REFIN2(+)
8
P0/REFIN2(−)
9
10
11
NC
AINCOM
AIN1
12
AIN2
Description
When the master clock for the device is provided externally by a crystal, the crystal is connected between
MCLK1 and MCLK2.
Master Clock Signal for the Device. The AD7192 has an internal 4.92 MHz clock. This internal clock can be
made available on the MCLK2 pin. The clock for the AD7192 can be provided externally also in the form of a
crystal or external clock. A crystal can be tied across the MCLK1 and MCLK2 pins. Alternatively, the MCLK2 pin
can be driven with a CMOS-compatible clock and the MCLK1 pin left unconnected.
Serial Clock Input. This serial clock input is for data transfers to and from the ADC. The SCLK has a Schmitttriggered input, making the interface suitable for opto-isolated applications. The serial clock can be
continuous with all data transmitted in a continuous train of pulses. Alternatively, it can be a noncontinuous
clock with the information transmitted to or from the ADC in smaller batches of data.
Chip Select Input. This is an active low logic input used to select the ADC. CS can be used to select the ADC in
systems with more than one device on the serial bus or as a frame synchronization signal in communicating
with the device. CS can be hardwired low, allowing the ADC to operate in 3-wire mode with SCLK, DIN, and
DOUT used to interface with the device.
Digital Output Pin. This pin can function as a general-purpose output bit referenced between AVDD and AGND.
Digital Output Pin. This pin can function as a general-purpose output bit referenced between AVDD and AGND.
Digital Output Pin/Positive Reference Input. This pin functions as a general-purpose output bit referenced
between AVDD and AGND. When the REFSEL bit in the configuration register = 1, this pin functions as REFIN2(+).
An external reference can be applied between REFIN2(+) and REFIN2(−). REFIN2(+) can lie anywhere between
AVDD and AGND + 1 V. The nominal reference voltage, (REFIN2(+) − REFIN2(−)), is AVDD, but the part functions
with a reference from 1 V to AVDD.
Digital Output Pin/Negative Reference Input. This pin functions as a general-purpose output bit referenced
between AVDD and AGND. When the REFSEL bit in the configuration register = 1, this pin functions as REFIN2(−).
This reference input can lie anywhere between AGND and AVDD − 1 V.
No Connect. This pin should be tied to AGND.
Analog inputs AIN1 to AIN4 are referenced to this input when configured for pseudodifferential operation.
Analog Input. This pin can be configured as the positive input of a fully differential input pair when used with
AIN2 or as a pseudodifferential input when used with AINCOM.
Analog Input. This pin can be configured as the negative input of a fully differential input pair when used
with AIN1 or as a pseudodifferential input when used with AINCOM.
Rev. A | Page 10 of 40
AD7192
Pin No.
13
Mnemonic
AIN3
14
AIN4
15
REFIN1(+)
16
17
18
19
20
REFIN1(−)
BPDSW
AGND
DGND
AVDD
21
DVDD
22
SYNC
23
DOUT/RDY
24
DIN
Description
Analog Input. This pin can be configured as the positive input of a fully differential input pair when used with
AIN4 or as a pseudodifferential input when used with AINCOM.
Analog Input. This pin can be configured as the negative input of a fully differential input pair when used
with AIN3 or as a pseudodifferential input when used with AINCOM.
Positive Reference Input. An external reference can be applied between REFIN1(+) and REFIN1(−). REFIN1(+)
can lie anywhere between AVDD and AGND + 1 V. The nominal reference voltage, (REFIN1(+) − REFIN1(−)), is
AVDD, but the part functions with a reference from 1 V to AVDD.
Negative Reference Input. This reference input can lie anywhere between AGND and AVDD − 1 V.
Bridge Power-Down Switch to AGND.
Analog Ground Reference Point.
Digital Ground Reference Point.
Analog Supply Voltage, 3 V to 5.25 V. AVDD is independent of DVDD. Therefore, DVDD can be operated at 3 V with
AVDD at 5 V or vice versa.
Digital Supply Voltage, 2.7 V to 5.25 V. DVDD is independent of AVDD. Therefore, AVDD can be operated at 3 V
with DVDD at 5 V or vice versa.
Logic input that allows for synchronization of the digital filters and analog modulators when using a number
of AD7192 devices. While SYNC is low, the nodes of the digital filter, the filter control logic, and the
calibration control logic are reset, and the analog modulator is also held in its reset state. SYNC does not
affect the digital interface but does reset RDY to a high state if it is low. SYNC has a pull-up resistor internally
to DVDD.
Serial Data Output/Data Ready Output. DOUT/RDYserves a dual purpose. It functions as a serial data output
pin to access the output shift register of the ADC. The output shift register can contain data from any of the
on-chip data or control registers. In addition, DOUT/RDY operates as a data ready pin, going low to indicate
the completion of a conversion. If the data is not read after the conversion, the pin goes high before the next
update occurs. The DOUT/RDY falling edge can be used as an interrupt to a processor, indicating that valid
data is available. With an external serial clock, the data can be read using the DOUT/RDY pin. With CS low, the
data-/control-word information is placed on the DOUT/RDY pin on the SCLK falling edge and is valid on the
SCLK rising edge.
Serial Data Input to the Input Shift Register on the ADC. Data in this shift register is transferred to the control
registers in the ADC, with the register selection bits of the communications register identifying the
appropriate register.
Rev. A | Page 11 of 40
AD7192
45
8,388,882
40
8,388,880
35
8,388,878
30
8,388,876
8,388,874
25
20
8,388,872
15
8,388,870
10
8,388,868
5
8,388,866
0
200
400
600
800
1000
SAMPLE
0
8,388,850
8,388,870
8,388,890
8,388,910
07822-009
OCCURRENCE
8,388,884
07822-006
CODE
TYPICAL PERFORMANCE CHARACTERISTICS
8,388,930
CODE
Figure 9. Noise Distribution Histogram (VREF = AVDD = 5 V,
Output Data Rate = 2400 Hz, Gain = 1, Chop Disabled, Sinc4 Filter)
Figure 6. Noise (VREF = AVDD = 5 V, Output Data Rate = 4.7 Hz,
Gain = 128, Chop Disabled, Sinc4 Filter)
8,389,050
200
8,389,000
8,388,950
8,388,900
CODE
OCCURRENCE
150
100
8,388,850
8,388,800
8,388,750
50
8,388,869
8,388,873
8,388,877
8,388,881
8,388,650
07822-007
0
8,388,865
8,388,885
CODE
0
200
400
600
800
1000
SAMPLE
Figure 10. Noise (VREF = AVDD = 5 V, Output Data Rate = 2400 Hz,
Gain = 128, Chop Disabled, Sinc4 Filter)
Figure 7. Noise Distribution Histogram (VREF = AVDD = 5 V,
Output Data Rate = 4.7 Hz, Gain = 128, Chop Disabled, Sinc4 Filter)
15
8,388,940
8,388,930
8,388,920
OCCURRENCE
8,388,910
8,388,890
8,388,880
10
5
8,388,870
8,388,860
8,388,840
0
200
400
600
800
1000
SAMPLE
Figure 8. Noise (VREF = AVDD = 5 V, Output Data Rate = 2400 Hz,
Gain = 1, Chop Disabled, Sinc4 Filter)
0
8,388,740
8,388,800
8,388,860
8,388,920
CODE
8,388,980
8,389,040
07822-011
8,388,850
07822-008
CODE
8,388,900
Figure 11. Noise Distribution Histogram (VREF = AVDD = 5 V,
Output Data Rate = 2400 Hz, Gain = 128, Chop Disabled, Sinc4 Filter)
Rev. A | Page 12 of 40
07822-010
8,388,700
AD7192
0.4
5
0.2
4
0
–0.2
OFFSET (µV)
INL (ppm of FSR)
3
2
1
–0.4
–0.6
–0.8
0
–1.0
–1
–2
–1
0
1
2
3
4
VIN (V)
–1.4
–60
–40
–20
0
20
40
60
80
100
120
TEMPERATURE (°C)
Figure 12. INL (Gain = 1)
07822-115
–3
07822-112
–2
–4
–1.2
Figure 15. Offset Error (Gain = 128, Chop Disabled)
20
1.000008
15
1.000006
1.000004
1.000002
5
1.000000
GAIN
INL (ppm of FSR)
10
0
0.999998
0.999996
–5
0.999994
–10
0.999992
–15
–0.01
0
0.01
0.02
0.03
VIN (V)
0.999988
–60
–40
128.002
166
128.000
164
127.998
GAIN
168
162
127.994
158
127.992
156
127.990
0
20
40
60
40
60
80
100
120
80
100
120
127.996
160
80
100
TEMPERATURE (°C)
120
07822-114
OFFSET (µV)
128.004
–20
20
Figure 16. Gain Error (Gain = 1)
170
–40
0
TEMPERATURE (°C)
Figure 13. INL (Gain = 128)
154
–60
–20
127.988
–60
–40
–20
0
20
40
60
TEMPERATURE (°C)
Figure 17. Gain Error (Gain = 128)
Figure 14. Offset Error (Gain = 1, Chop Disabled)
Rev. A | Page 13 of 40
07822-117
–0.02
07822-116
0.999990
07822-113
–20
–0.03
AD7192
RMS NOISE AND RESOLUTION
The AD7192 has a choice of two filter types: sinc4 and sinc3.
In addition, the AD7192 can be operated with chop enabled
or chop disabled.
The following tables show the rms noise of the AD7192 for some
of the output data rates and gain settings with chop disabled
and enabled for the sinc4 and sinc3 filters. The numbers given
are for the bipolar input range with the external 5 V reference.
These numbers are typical and are generated with a differential
input voltage of 0 V when the ADC is continuously converting
on a single channel. The effective resolution is also shown, and
the output peak-to-peak (p-p) resolution, or noise-free resolution,
is listed in parentheses. It is important to note that the effective
resolution is calculated using the rms noise, whereas the p-p
resolution is calculated based on peak-to-peak noise. The p-p
resolution represents the resolution for which there is no code
flicker. These numbers are typical and are rounded to the
nearest ½ LSB.
SINC4 CHOP DISABLED
Table 6. RMS Noise (nV) vs. Gain and Output Data Rate
Filter Word
(Decimal)
1023
640
480
96
80
40
32
16
5
2
1
Output
Data Rate
(Hz)
4.7
7.5
10
50
60
120
150
300
960
2400
4800
Settling
Time
(ms)
852.5
533
400
80
66.7
33.3
26.7
13.3
4.17
1.67
0.83
Gain of 1
350
425
490
2000
2100
2400
2500
3100
4800
7500
16,300
Gain of 8
50
62
85
260
273
315
335
420
690
1100
2200
Gain of 16
30
36
43
134
139
175
185
240
390
640
1200
Gain of 32
18
21
23
73
77
95
110
145
240
390
670
Gain of 64
13
15
17
46
48
64
71
95
170
273
427
Gain of 128
11
13
15
34
38
51
58
81
145
235
345
Table 7. Effective Resolution (Peak-to-Peak Resolution) vs. Gain and Output Data Rate
Filter Word
(Decimal)
1023
640
480
96
80
40
32
16
5
2
1
1
Output
Data Rate
(Hz)
4.7
7.5
10
50
60
120
150
300
960
2400
4800
Settling
Time
(ms)
852.5
533
400
80
66.7
33.3
26.7
13.3
4.17
1.67
0.83
Gain of 1 1
24 (22)
24 (22)
24 (21.5)
22 (19.5)
22 (19.5)
22 (19.5)
21.5 (19)
21.5 (19)
20.5 (18)
20 (17.5)
19 (16.5)
Gain of 81
24 (22)
24 (21.5)
23.5 (21)
22 (19.5)
22 (19.5)
21.5 (19)
21.5 (19)
21.5 (19)
20.5 (18)
20 (17.5)
19 (16.5)
Gain of 161
24 (21.5)
24 (21.5)
23.5 (21)
22 (19.5)
22 (19.5)
21.5 (19)
21.5 (19)
21 (18.5)
20.5 (18)
19.5 (17)
19 (16.5)
The output peak-to-peak (p-p) resolution is listed in parentheses.
Rev. A | Page 14 of 40
Gain of 321
24 (21.5)
23.5 (21)
23.5 (21)
22 (19.5)
21.5 (19)
21.5 (19)
21 (18.5)
21 (18.5)
20 (17.5)
19.5 (17)
18.5 (16)
Gain of 641
23.5 (21)
23 (20.5)
23 (20.5)
21.5 (19)
21.5 (19)
21 (18.5)
21 (18.5)
20.5 (18)
19.5 (17)
19 (16.5)
18.5 (16)
Gain of 1281
22.5 (20)
22.5 (20)
22 (19.5)
21 (18.5)
20.5 (18)
20.5 (18)
20 (17.5)
19.5 (17)
19 (16.5)
18 (15.5)
17.5 (15)
AD7192
SINC3 CHOP DISABLED
Table 8. RMS Noise (nV) vs. Gain and Output Data Rate
Filter Word
(Decimal)
1023
640
480
96
80
40
32
16
5
2
1
Output
Data Rate
(Hz)
4.7
7.5
10
50
60
120
150
300
960
2400
4800
Settling
Time (ms)
639.4
400
300
60
50
25
20
10
3.13
1.25
0.625
Gain of 1
350
440
500
2000
2100
2400
2500
3100
5300
55800
446,000
Gain of 8
51
62
87
255
273
315
335
425
745
7100
55,400
Gain of 16
30
36
45
134
139
168
185
235
415
3600
28,000
Gain of 32
18
22
26
73
77
96
105
136
250
1750
14,000
Gain of 64
15
18
19
47
49
66
73
100
180
910
7000
Gain of 128
12
15
17
36
40
55
62
86
156
500
3500
Table 9. Effective Resolution (Peak-to-Peak Resolution) vs. Gain and Output Data Rate
Filter Word
(Decimal)
1023
640
480
96
80
40
32
16
5
2
1
1
Output
Data Rate
(Hz)
4.7
7.5
10
50
60
120
150
300
960
2400
4800
Settling
Time (ms)
639.4
400
300
60
50
25
20
10
3.13
1.25
0.625
Gain of 1 1
24 (22)
24 (21.5)
24 (21.5)
22 (19.5)
22 (19.5)
22 (19.5)
21.5 (19)
21.5 (19)
20.5 (18)
17 (14.5)
14 (11.5)
Gain of 81
24 (22)
24 (21.5)
23.5 (21)
22 (19.5)
22 (19.5)
21.5 (19)
21.5 (19)
21.5 (19)
20.5 (18)
17 (14.5)
14 (11.5)
Gain of 161
24 (21.5)
24 (21.5)
23.5 (21)
22 (19.5)
22 (19.5)
21.5 (19)
21.5 (19)
21 (18.5)
20.5 (18)
17 (14.5)
14 (11.5)
The output peak-to-peak (p-p) resolution is listed in parentheses.
Rev. A | Page 15 of 40
Gain of 321
24 (21.5)
23.5 (21)
23.5 (21)
22 (19.5)
21.5 (19)
21.5 (19)
21.5 (19)
21 (18.5)
20 (17.5)
17 (14.5)
14 (11.5)
Gain of 641
23 (20.5)
23 (20.5)
22.5 (20)
21.5 (19)
21.5 (19)
21 (18.5)
21 (18.5)
20.5 (18)
19.5 (17)
17 (14.5)
14 (11.5)
Gain of 1281
22.5 (20)
22 (19.5)
22 (19.5)
21 (18.5)
20.5 (18)
20 (17.5)
20 (17.5)
19.5 (17)
18.5 (16)
17 (14.5)
14 (11.5)
AD7192
SINC4 CHOP ENABLED
Table 10. RMS Noise (nV) vs. Gain and Output Data Rate
Filter Word
(Decimal)
1023
640
480
96
80
40
32
16
5
2
1
Output
Data Rate
(Hz)
1.175
1.875
2.5
12.5
15
30
37.5
75
240
600
1200
Settling
Time (ms)
1702
1067
800
160
133
66.7
53.3
26.7
8.33
3.33
1.67
Gain of 1
248
301
347
1420
1490
1700
1770
2200
3400
5310
11,600
Gain of 8
36
44
61
184
194
223
237
297
488
780
1560
Gain of 16
22
26
31
95
99
124
131
170
276
453
849
Gain of 32
13
15
17
52
55
68
78
103
170
276
474
Gain of 64
9
11
13
33
34
46
51
68
121
194
302
Gain of 128
8
10
11
25
27
37
42
58
103
167
244
Gain of 641
24 (21.5)
23.5 (21)
23.5 (21)
22 (19.5)
22 (19.5)
21.5 (19)
21.5 (19)
21 (18.5)
20 (17.5)
19.5 (17)
19 (16.5)
Gain of 1281
23 (20.5)
23 (20.5)
22.5 (20)
21.5 (19)
21 (18.5)
21 (18.5)
20.5 (18)
20 (17.5)
19.5 (17)
18.5 (16)
18 (15.5)
Table 11. Effective Resolution (Peak-to-Peak Resolution) vs. Gain and Output Data Rate
Filter Word
(Decimal)
1023
640
480
96
80
40
32
16
5
2
1
1
Output
Data Rate
(Hz)
1.175
1.875
2.5
12.5
15
30
37.5
75
240
600
1200
Settling
Time (ms)
1702
1067
800
160
133
66.7
53.3
26.7
8.33
3.33
1.67
Gain of 1 1
24 (22.5)
24 (22.5)
24 (22)
22.5 (20)
22.5 (20)
22.5 (20)
22 (19.5)
22 (19.5)
21 (18.5)
20.5 (18)
19.5 (17)
Gain of 81
24 (22.5)
24 (22)
24 (21.5)
22.5 (20)
22.5 (20)
22 (19.5)
22 (19.5)
22 (19.5)
21 (18.5)
20.5 (18)
19.5 (17)
Gain of 161
24 (22)
24 (22)
24 (21.5)
22.5 (20)
22.5 (20)
22 (19.5)
22 (19.5)
21.5 (19)
21 (18.5)
20 (17.5)
19.5 (17)
The output peak-to-peak (p-p) resolution is listed in parentheses.
Rev. A | Page 16 of 40
Gain of 321
24 (22)
24 (21.5)
24 (21.5)
22.5 (20)
22 (19.5)
22 (19.5)
21.5 (19)
21.5 (19)
20.5 (18)
20 (17.5)
19 (16.5)
AD7192
SINC3 CHOP ENABLED
Table 12. RMS Noise (nV) vs. Gain and Output Data Rate
Filter Word
(Decimal)
1023
640
480
96
80
40
32
16
5
2
1
Output
Data Rate
(Hz)
1.56
2.5
3.33
16.6
20
40
50
100
320
800
1600
Settling
Time (ms)
1282
800
600
120
100
50
40
20
6.25
2.5
1.25
Gain of 1
248
312
354
1415
1485
1698
1768
2193
3748
39500
315,400
Gain of 8
37
44
62
181
194
223
237
301
527
5020
39,200
Gain of 16
22
26
32
95
99
119
131
167
294
2546
19,800
Gain of 32
13
16
19
52
55
68
75
97
177
1240
9900
Gain of 64
11
13
14
34
35
47
52
71
128
644
4950
Gain of 128
9
11
13
26
29
39
44
61
111
354
2500
Table 13. Effective Resolution (Peak-to-Peak Resolution) vs. Gain and Output Data Rate
Filter Word
(Decimal)
1023
640
480
96
80
40
32
16
5
2
1
1
Output
Data Rate
(Hz)
1.56
2.5
3.33
16.6
20
40
320
100
320
800
1600
Settling
Time (ms)
1282
800
600
120
100
50
40
20
6.25
2.5
1.25
Gain of 1 1
24 (22.5)
24 (22)
24 (22)
22.5 (20)
22.5 (20)
22.5 (20)
22 (19.5)
22(19.5)
21 (18.5)
17.5 (15)
14.5 (12)
Gain of 81
24 (22.5)
24 (22)
24 (21.5)
22.5 (20)
22.5 (20)
22 (19.5)
22 (19.5)
22 (19.5)
20.5 (18)
17.5 (15)
14.5 (12)
Gain of 161
24 (22)
24 (22)
24 (21.5)
22.5 (20)
22.5 (20)
22 (19.5)
22 (19.5)
21.5 (19)
20.5 (18)
17.5 (15)
14.5 (12)
The output peak-to-peak (p-p) resolution is listed in parentheses.
Rev. A | Page 17 of 40
Gain of 321
24 (22)
24 (21.5)
24 (21.5)
22.5 (20)
22 (19.5)
22 (19.5)
22 (19.5)
21.5 (19)
20 (17.5)
17.5 (15)
14.5 (12)
Gain of 641
23.5 (21)
23.5 (21)
23 (20.5)
22 (19.5)
22 (19.5)
21.5 (19)
21.5 (19)
21 (18.5)
19.5 (17)
17.5 (15)
14.5 (12)
Gain of 1281
23 (20.5)
22.5 (20)
22.5 (20)
21.5 (19)
21 (18.5)
20.5 (18)
20.5 (18)
20 (17.5)
18.5 (16)
17.5 (15)
14.5 (12)
AD7192
ON-CHIP REGISTERS
The ADC is controlled and configured via a number of on-chip
registers that are described on the following pages. In the
following descriptions, “set” implies a Logic 1 state and
“cleared” implies a Logic 0 state, unless otherwise noted.
COMMUNICATIONS REGISTER
(RS2, RS1, RS0 = 0, 0, 0)
The communications register is an 8-bit write-only register. All
communications to the part must start with a write operation to
the communications register. The data written to the communications register determines whether the next operation is a read
or write operation and in which register this operation takes
place. For read or write operations, when the subsequent read
CR7
WEN(0)
CR6
R/W(0)
CR5
RS2(0)
CR4
RS1(0)
or write operation to the selected register is complete, the
interface returns to where it expects a write operation to the
communications register. This is the default state of the
interface and, on power-up or after a reset, the ADC is in this
default state waiting for a write operation to the communications register. In situations where the interface sequence is lost,
a write operation of at least 40 serial clock cycles with DIN high
returns the ADC to this default state by resetting the entire part.
Table 14 outlines the bit designations for the communications
register. CR0 through CR7 indicate the bit location, CR denoting
that the bits are in the communications register. CR7 denotes
the first bit of the data stream. The number in parentheses
indicates the power-on/reset default status of that bit.
CR3
RS0(0)
CR2
CREAD(0)
CR1
0(0)
CR0
0(0)
Table 14. Communications Register Bit Designations
Bit Location
CR7
Bit Name
WEN
CR6
R/W
CR5 to CR3
RS2 to RS0
CR2
CREAD
CR1 to CR0
0
Description
Write enable bit. A 0 must be written to this bit so that the write to the communications register actually
occurs. If a 1 is the first bit written, the part does not clock on to subsequent bits in the register. It stays at
this bit location until a 0 is written to this bit. After a 0 is written to the WEN bit, the next seven bits are
loaded to the communications register. Idling the DIN pin high between data transfers minimizes the
effects of spurious SCLK pulses on the serial interface.
A 0 in this bit location indicates that the next operation is a write to a specified register. A 1 in this position
indicates that the next operation is a read from the designated register.
Register address bits. These address bits are used to select which registers of the ADC are selected during
the serial interface communication (see Table 15).
Continuous read of the data register. When this bit is set to 1 (and the data register is selected), the serial
interface is configured so that the data register can be continuously read; that is, the contents of the data
register are automatically placed on the DOUT pin when the SCLK pulses are applied after the RDY pin
goes low to indicate that a conversion is complete. The communications register does not have to be
written to for subsequent data reads. To enable continuous read, the Instruction 01011100 must be written
to the communications register. To disable continuous read, the Instruction 01011000 must be written to
the communications register while the RDY pin is low. While continuous read is enabled, the ADC monitors
activity on the DIN line so that it can receive the instruction to disable continuous read. Additionally, a reset
occurs if 40 consecutive 1s are seen on DIN. Therefore, DIN should be held low until an instruction is to be
written to the device.
These bits must be programmed to Logic 0 for correct operation.
Table 15. Register Selection
RS2
0
0
0
0
0
1
1
1
1
RS1
0
0
0
1
1
0
0
1
1
RS0
0
0
1
0
1
0
1
0
1
Register
Communications register during a write operation
Status register during a read operation
Mode register
Configuration register
Data register/data register plus status information
ID register
GPOCON register
Offset register
Full-scale register
Rev. A | Page 18 of 40
Register Size
8 bits
8 bits
24 bits
24 bits
24 bits/32 bits
8 bits
8 bits
24 bits
24 bits
AD7192
STATUS REGISTER
(RS2, RS1, RS0 = 0, 0, 0; Power-On/Reset = 0x80)
The status register is an 8-bit read-only register. To access the ADC status register, the user must write to the communications register,
select the next operation to be a read, and load Bit RS2, Bit RS1, and Bit RS0 with 0. Table 16 outlines the bit designations for the status
register. SR0 through SR7 indicate the bit locations, SR denoting that the bits are in the status register. SR7 denotes the first bit of the data
stream. The number in parentheses indicates the power-on/reset default status of that bit.
SR7
RDY(1)
SR6
ERR(0)
SR5
NOREF(0)
SR4
PARITY(0)
SR3
0(0)
SR2
CHD2(0)
SR1
CHD1(0)
SR0
CHD0(0)
Table 16. Status Register Bit Designations
Bit Location
SR7
Bit Name
RDY
SR6
ERR
SR5
NOREF
SR4
PARITY
SR3
SR2 to SR0
0
CHD2 to
CHD0
Description
Ready bit for the ADC. This bit is cleared when data is written to the ADC data register. The RDY bit is set
automatically after the ADC data register is read, or a period of time before the data register is updated,
with a new conversion result to indicate to the user that the conversion data should not be read. It is also
set when the part is placed in power-down mode or idle mode or when SYNC is taken low.
The end of a conversion is also indicated by the DOUT/RDY pin. This pin can be used as an alternative to
the status register for monitoring the ADC for conversion data.
ADC error bit. This bit is written to at the same time as the RDY bit. This bit is set to indicate that the result
written to the ADC data register is clamped to all 0s or all 1s. Error sources include overrange or underrange or the absence of a reference voltage. This bit is cleared when the result written to the data register is
within the allowed analog input range again.
No external reference bit. This bit is set to indicate that the selected reference (REFIN1 or REFIN2) is at a
voltage that is below a specified threshold. When set, conversion results are clamped to all 1s. This bit is
cleared to indicate that a valid reference is applied to the selected reference pins. The NOREF bit is enabled
by setting the REFDET bit in the configuration register to 1.
Parity check of the data register. If the ENPAR bit in the mode register is set, the PARITY bit is set if there is
an odd number of 1s in the data register. It is cleared if there is an even number of 1s in the data register.
The DAT_STA bit in the mode register should be set when the parity check is used. When the DAT_STA bit is
set, the contents of the status register are transmitted along with the data for each data register read.
This bit is set to 0.
These bits indicate which channel corresponds to the data register contents. They do not indicate which
channel is presently being converted but indicate which channel was selected when the conversion
contained in the data register was generated.
MODE REGISTER
(RS2, RS1, RS0 = 0, 0, 1; Power-On/Reset = 0x080060)
The mode register is a 24-bit register from which data can be read or to which data can be written. This register is used to select the
operating mode, the output data rate, and the clock source. Table 17 outlines the bit designations for the mode register. MR0 through
MR23 indicate the bit locations, MR denoting that the bits are in the mode register. MR23 denotes the first bit of the data stream. The
number in parentheses indicates the power-on/reset default status of that bit. Any write to the mode register resets the modulator and
filter and sets the RDY bit.
MR23
MD2(0)
MR15
SINC3(0)
MR7
FS7(0)
MR22
MD1(0)
MR14
0
MR6
FS6(1)
MR21
MD0(0)
MR13
ENPAR(0)
MR5
FS5(1)
MR20
DAT_STA(0)
MR12
CLK_DIV(0)
MR4
FS4(0)
MR19
CLK1(1)
MR11
SINGLE(0)
MR3
FS3(0)
Rev. A | Page 19 of 40
MR18
CLK0(0)
MR10
REJ60(0)
MR2
FS2(0)
MR17
0
MR9
FS9(0)
MR1
FS1(0)
MR16
0
MR8
FS8(0)
MR0
FS0(0)
AD7192
Table 17. Mode Register Bit Designations
Bit Location
MR23 to MR21
MR20
Bit Name
MD2 to MD0
DAT_STA
MR19, MR18
CLK1, CLK0
MR17, MR16
MR15
0
SINC3
MR14
MR13
0
ENPAR
MR12
CLK_DIV
MR11
SINGLE
MR10
REJ60
MR9 to MR0
FS9 to FS0
Description
Mode select bits. These bits select the operating mode of the AD7192 (see Table 18).
This bit enables the transmission of status register contents after each data register read. When
DAT_STA is set, the contents of the status register are transmitted along with each data register read.
This function is useful when several channels are selected because the status register identifies the
channel to which the data register value corresponds.
These bits are used to select the clock source for the AD7192. Either the on-chip 4.92 MHz clock or an
external clock can be used. The ability to use an external clock allows several AD7192 devices to be
synchronized. Also, 50 Hz/60 Hz rejection is improved when an accurate external clock drives the
AD7192.
CLK1
CLK0
ADC Clock Source
0
0
External crystal. The external crystal is connected from MCLK1 to MCLK2.
0
1
External clock. The external clock is applied to the MCLK2 pin.
1
0
Internal 4.92 MHz clock. Pin MCLK2 is tristated.
1
1
Internal 4.92 MHz clock. The internal clock is available on MCLK2.
These bits must be programmed with a Logic 0 for correct operation.
Sinc3 filter select bit. When this bit is cleared, the sinc4 filter is used (default value). When this bit is set,
the sinc3 filter is used. The benefit of the sinc3 filter compared to the sinc4 filter is its lower settling time.
For a given output data rate, fADC, the sinc3 filter has a settling time of 3/fADC while the sinc4 filter has a
settling time of 4/fADC when chop is disabled. The sinc4 filter, due to its deeper notches, gives better
50 Hz/60 Hz rejection. At low output data rates, both filters give similar rms noise and similar no
missing codes for a given output data rate. At higher output data rates (FS values less than 5), the sinc4
filter gives better performance than the sinc3 filter for rms noise and no missing codes.
This bit must be programmed with a Logic 0 for correct operation.
Enable parity bit. When ENPAR is set, parity checking on the data register is enabled. The DAT_STA bit
in the mode register should be set when the parity check is used. When the DAT_STA bit is set, the
contents of the status register are transmitted along with the data for each data register read.
Clock Divide by 2. When CLK_DIV is set, the master clock is divided by 2. For normal conversions, this
bit should be set to 0. When performing internal full-scale calibrations, this bit must be set when AVDD
is less than 4.75 V. The calibration accuracy is optimized when chop is enabled and a low output data
rate is used while performing the calibration. When AVDD is greater than or equal to 4.75 V, it is not
compulsory to set the CLK_DIV bit when performing internal full-scale calibrations.
Single cycle conversion enable bit. When this bit is set, the AD7192 settles in one conversion cycle so
that it functions as a zero-latency ADC. This bit has no effect when multiple analog input channels are
enabled or when the single conversion mode is selected.
This bit enables a notch at 60 Hz when the first notch of the sinc filter is at 50 Hz. When REJ60 is set, a
filter notch is placed at 60 Hz when the sinc filter first notch is at 50 Hz. This allows simultaneous 50 Hz/
60 Hz rejection.
Filter output data rate select bits. The 10 bits of data programmed into these bits determine the filter
cut-off frequency, the position of the first notch of the filter, and the output data rate for the part. In
association with the gain selection, they also determine the output noise (and, therefore, the effective
resolution) of the device (see Table 6 through Table 13). When chop is disabled and continuous
conversion mode is selected,
Output Data Rate = (MCLK/1024)/FS
where FS is the decimal equivalent of the code in Bit FS0 to Bit FS9 and is in the range 1 to 1023, and
MCLK is the master clock frequency. With a nominal MCLK of 4.92 MHz, this results in an output data
rate from 4.69 Hz to 4.8 kHz. With chop disabled, the first notch frequency is equal to the output data
rate when converting on a single channel. When chop is enabled,
Output Data Rate = (MCLK/1024)/(N x FS)
where FS is the decimal equivalent of the code in Bit FS0 to Bit FS9 and is in the range 1 to 1023, and
MCLK is the master clock frequency. With a nominal MCLK of 4.92 MHz, this results in a conversion rate
from 4.69/N Hz to 4.8/N kHz, where N is the order of the sinc filter. The sinc filter’s first notch frequency
is equal to N × output data rate. The chopping introduces notches at odd integer multiples of (output
data rate/2).
Rev. A | Page 20 of 40
AD7192
Table 18. Operating Modes
MD2
0
MD1
0
MD0
0
0
0
1
0
1
0
0
1
1
1
0
0
1
0
1
1
1
0
1
1
1
Mode
Continuous conversion mode (default). In continuous conversion mode, the ADC continuously performs
conversions and places the result in the data register. The DOUT/RDY pin and the RDY bit in the status register go
low when a conversion is complete. The user can read these conversions by setting the CREAD bit in the communications register to 1, which enables continuous read. When continuous read is enabled, the conversions are
automatically placed on the DOUT line when SCLK pulses are applied. Alternatively, the user can instruct the ADC to
output each conversion by writing to the communications register. After power-on, a reset, or a reconfiguration of
the ADC, the complete settling time of the filter is required to generate the first valid conversion. Subsequent
conversions are available at the selected output data rate, which is dependent on filter choice.
Single conversion mode. When single conversion mode is selected, the ADC powers up and performs a single
conversion on the selected channel. The internal clock requires up to 1 ms to power up and settle. The ADC then
performs the conversion, which requires the complete settling time of the filter. The conversion result is placed in
the data register. RDY goes low, and the ADC returns to power-down mode. The conversion remains in the data
register until another conversion is performed. RDY remains active (low) until the data is read or another conversion
is performed.
Idle mode. In idle mode, the ADC filter and modulator are held in a reset state even though the modulator clocks are
still provided.
Power-down mode. In power-down mode, all AD7192 circuitry, except the bridge power-down switch, is powered
down. The bridge power-down switch remains active because the user may need to power up the sensor prior to
powering up the AD7192 for settling reasons. The external crystal, if selected, remains active.
Internal zero-scale calibration. An internal short is automatically connected to the input. RDY goes high when the
calibration is initiated and returns low when the calibration is complete. The ADC is placed in idle mode following a
calibration. The measured offset coefficient is placed in the offset register of the selected channel.
Internal full-scale calibration. A full-scale input voltage is automatically connected to the input for this calibration.
RDY goes high when the calibration is initiated and returns low when the calibration is complete. The ADC is placed
in idle mode following a calibration. The measured full-scale coefficient is placed in the full-scale register of the
selected channel. A full-scale calibration is required each time the gain of a channel is changed to minimize the fullscale error. When AVDD is less than 4.75 V, the CLK_DIV bit must be set when performing the internal full-scale
calibration.
System zero-scale calibration. The user should connect the system zero-scale input to the channel input pins as
selected by the CH7 to CH0 bits in the configuration register. RDY goes high when the calibration is initiated and
returns low when the calibration is complete. The ADC is placed in idle mode following a calibration. The measured
offset coefficient is placed in the offset register of the selected channel. A system zero-scale calibration is required
each time the gain of a channel is changed.
System full-scale calibration. The user should connect the system full-scale input to the channel input pins as
selected by the CH7 to CH0 bits in the configuration register. RDY goes high when the calibration is initiated and
returns low when the calibration is complete. The ADC is placed in idle mode following a calibration. The measured
full-scale coefficient is placed in the full-scale register of the selected channel. A full-scale calibration is required
each time the gain of a channel is changed.
CONFIGURATION REGISTER
(RS2, RS1, RS0 = 0, 1, 0; Power-On/Reset = 0x000117)
The configuration register is a 24-bit register from which data can be read or to which data can be written. This register is used to
configure the ADC for unipolar or bipolar mode, to enable or disable the buffer, to enable or disable the burnout currents, to select the
gain, and to select the analog input channel.
Table 19 outlines the bit designations for the filter register. CON0 through CON23 indicate the bit locations. CON denotes that the bits
are in the configuration register. CON23 denotes the first bit of the data stream. The number in parentheses indicates the power-on/reset
default status of that bit.
CON23
CHOP(0)
CON15
CH7(0)
CON7
BURN(0)
CON22
0(0)
CON14
CH6(0)
CON6
REFDET(0)
CON21
0(0)
CON13
CH5(0)
CON5
0(0)
CON20
REFSEL(0)
CON12
CH4(0)
CON4
BUF(1)
CON19
0(0)
CON11
CH3(0)
CON3
U/B (0)
Rev. A | Page 21 of 40
CON18
0(0)
CON10
CH2(0)
CON2
G2(1)
CON17
0(0)
CON9
CH1(0)
CON1
G1(1)
CON16
(0)
CON8
CH0(1)
CON0
G0(1)
AD7192
Table 19. Configuration Register Bit Designations
Bit Location
CON23
Bit Name
CHOP
CON22, CON21
CON20
0
REFSEL
CON19 to CON16
CON15 to CON8
0
CH7 to CH0
CON7
BURN
CON6
REFDET
CON5
CON4
0
BUF
CON3
U/B
CON2 to CON0
G2 to G0
Description
Chop enable bit. When the CHOP bit is cleared, chop is disabled. When the CHOP bit is set, chop is
enabled. When chop is enabled, the offset and offset drift of the ADC are continuously removed.
However, this increases the conversion time and settling time of the ADC. For example, when FS = 96
decimal and the sinc4 filter is selected, the conversion time with chop enabled equals 80 ms and the
settling time equals 160 ms. With chop disabled, higher conversion rates are allowed. For an FS word of
96 decimal and the sinc4 filter selected, the conversion time is 20 ms and the settling time is 80 ms.
However, at low gains, periodic calibrations may be required to remove the offset and offset drift.
These bits must be programmed with a Logic 0 for correct operation.
Reference select bits. The reference source for the ADC is selected using these bits.
REFSEL
Reference Voltage
0
External reference applied between REFIN1(+) and REFIN1(−).
1
External reference applied between the P1/REFIN2(+) and P0/REFIN2(−) pins.
These bits must be programmed with a Logic 0 for correct operation.
Channel select bits. These bits are used to select which channels are enabled on the AD7192 (see Table 20).
Several channels can be selected, and the AD7192 automatically sequences them. The conversion on
each channel requires the complete settling time. When performing calibrations or when accessing the
calibration registers, only one channel can be selected.
When this bit is set to 1, the 500 nA current sources in the signal path are enabled. When BURN = 0, the
burnout currents are disabled. The burnout currents can be enabled only when the buffer is active and
when chop is disabled.
Enables the reference detect function. When set, the NOREF bit in the status register indicates when the
external reference being used by the ADC is open circuit or less than 0.6 V maximum. The reference
detect circuitry operates only when the ADC is active.
This bit must be programmed with a Logic 0 for correct operation.
Enables the buffer on the analog inputs. If cleared, the analog inputs are unbuffered, lowering the
power consumption of the device. If this bit is set, the analog inputs are buffered, allowing the user to
place source impedances on the front end without contributing gain errors to the system. With the
buffer disabled, the voltage on the analog input pins can be from 50 mV below AGND to 50 mV above
AVDD. When the buffer is enabled, it requires some headroom; therefore, the voltage on any input pin
must be limited to 250 mV within the power supply rails.
Polarity select bit. When this bit is set, unipolar operation is selected. When this bit is cleared, bipolar
operation is selected.
Gain select bits. These bits are written by the user to select the ADC input range as follows:
G2
G1
G0
Gain
ADC Input Range (5 V Reference)
0
0
0
1
±5 V
0
0
1
Reserved
0
1
0
Reserved
0
1
1
8
±625 mV
1
0
0
16
±312.5 mV
1
0
1
32
±156.2 mV
1
1
0
64
±78.125 mV
1
1
1
128
±39.06 mV
Rev. A | Page 22 of 40
AD7192
Table 20. Channel Selection
Channel Enable Bits in the Configuration Register
CH7
CH6
CH5
CH4
CH3
CH2
CH1
CH0
1
1
1
1
1
1
1
1
Channel Enabled
Positive Input
Negative Input
AIN(+)
AIN(−)
AIN1
AIN2
AIN3
AIN4
Temperature sensor
AIN2
AIN2
AIN1
AINCOM
AIN2
AINCOM
AIN3
AINCOM
AIN4
AINCOM
Status Register
Bits CHD[2:0]
000
001
010
011
100
101
110
111
Calibration
Register Pair
0
1
None
0
0
1
2
3
ID REGISTER
DATA REGISTER
(RS2, RS1, RS0 = 1, 0, 0; Power-On/Reset = 0xX0)
(RS2, RS1, RS0 = 0, 1, 1; Power-On/Reset = 0x000000)
The conversion result from the ADC is stored in this data
register. This is a read-only, 24-bit register. On completion of a
read operation from this register, the RDY pin/bit is set. When
the DAT_STA bit in the mode register is set to 1, the contents of
the status register are appended to each 24-bit conversion. This
is advisable when several analog input channels are enabled
because the three LSBs of the status register (CHD2 to CHD0)
identify the channel from which the conversion originated.
The identification number for the AD7192 is stored in the ID
register. This is a read-only register.
Rev. A | Page 23 of 40
AD7192
GPOCON REGISTER
(RS2, RS1, RS0 = 1, 0, 1; Power-On/Reset = 0x00)
The GPOCON register is an 8-bit register from which data can
be read or to which data can be written. This register is used to
enable the general-purpose digital outputs.
GP7
0(0)
GP6
BPDSW(0)
GP5
GP32EN(0)
GP4
GP10EN(0)
Table 21 outlines the bit designations for the GPOCON register.
GP0 through GP7 indicate the bit locations. GP denotes that the
bits are in the GPOCON register. GP7 denotes the first bit of
the data stream. The number in parentheses indicates the
power-on/reset default status of that bit.
GP3
P3DAT(0)
GP2
P2DAT(0)
GP1
P1DAT(0)
GP0
P0DAT(0)
Table 21. Register Bit Designations
Bit Location
GP7
GP6
Bit Name
0
BPDSW
GP5
GP32EN
GP4
GP10EN
GP3
P3DAT
GP2
P2DAT
GP1
P1DAT
GP0
P0DAT
Description
This bit must be programmed with a Logic 0 for correct operation.
Bridge power-down switch control bit. This bit is set by the user to close the bridge power-down switch
BPDSW to AGND. The switch can sink up to 30 mA. The bit is cleared by the user to open the bridge power–
down switch. When the ADC is placed in power-down mode, the bridge power-down switch remains active.
Digital Output P3 and Digital Output P2 enable. When GP32EN is set, the P3 and P2 digital outputs are
active. When GP32EN is cleared, the P3 and P2 pins are tristated, and the P3DAT and P2DAT bits are ignored.
Digital Output P1 and Digital Output P0 enable. When GP10EN is set, the P1 and P0 digital outputs are
active. When GP10EN is cleared, the P1 and P0 outputs are tristated, and the P1DAT and P0DAT bits are
ignored. The P1 and P0 pins can be used as a reference input to REFIN2 when the REFSEL bit in the
configuration register is set to 1.
Digital Output P3. When GP32EN is set, the P3DAT bit sets the value of the P3 general-purpose output pin.
When P3DAT is high, the P3 output pin is high. When P3DAT is low, the P3 output pin is low. When the
GPOCON register is read, the P3DAT bit reflects the status of the P3 pin if GP32EN is set.
Digital Output P2. When GP32EN is set, the P2DAT bit sets the value of the P2 general-purpose output pin.
When P2DAT is high, the P2 output pin is high. When P2DAT is low, the P2 output pin is low. When the
GPOCON register is read, the P2DAT bit reflects the status of the P2 pin if GP32EN is set.
Digital Output P1. When GP10EN is set, the P1DAT bit sets the value of the P1 general-purpose output pin.
When P1DAT is high, the P1 output pin is high. When P1DAT is low, the P1 output pin is low. When the
GPOCON register is read, the P1DAT bit reflects the status of the P1 pin if GP10EN is set.
Digital Output P0. When GP10EN is set, the P0DAT bit sets the value of the P0 general-purpose output pin.
When P0DAT is high, the P0 output pin is high. When P0DAT is low, the P0 output pin is low. When the
GPOCON register is read, the P0DAT bit reflects the status of the P0 pin if GP10EN is set.
OFFSET REGISTER
FULL-SCALE REGISTER
(RS2, RS1, RS0 = 1, 1, 0; Power-On/Reset = 0x800000)
(RS2, RS1, RS0 = 1, 1, 1; Power-On/Reset = 0x5XXXX0)
The offset register holds the offset calibration coefficient for the
ADC. The power-on reset value of the offset register is
0x800000. The AD7192 has four offset registers; therefore, each
channel has a dedicated offset register (see Table 20). Each of
these registers is a 24-bit read/write register. This register is
used in conjunction with its associated full-scale register to
form a register pair. The power-on reset value is automatically
overwritten if an internal or system zero-scale calibration is
initiated by the user. The AD7192 must be placed in powerdown mode or idle mode when writing to the offset register.
The full-scale register is a 24-bit register that holds the full-scale
calibration coefficient for the ADC. The AD7192 has four fullscale registers; therefore, each channel has a dedicated full-scale
register (see Table 20). The full-scale registers are read/write
registers. However, when writing to the full-scale registers, the
ADC must be placed in power-down mode or idle mode. These
registers are configured at power-on with factory-calibrated
full-scale calibration coefficients, the calibration being performed
at gain = 1. Therefore, every device has different default coefficients. The default value is automatically overwritten if an
internal or system full-scale calibration is initiated by the user
or if the full-scale register is written to.
Rev. A | Page 24 of 40
AD7192
ADC CIRCUIT INFORMATION
5V
REFIN1(+) AGND
IN+
OUT+
OUT–
IN–
AIN1
AIN2
AIN3
AIN4
AINCOM MUX
DVDD DGND
AVDD
REFERENCE
DETECT
AVDD
Σ-Δ
ADC
PGA
DOUT/RDY
SERIAL
INTERFACE
AND
CONTROL
LOGIC
DIN
SCLK
CS
SYNC
AGND
TEMP
SENSOR
REFIN1(–)
P3
P2
BPDSW
AD7192
CLOCK
CIRCUITRY
MCLK1 MCLK2
07822-012
AGND
P0/REFIN2(–) P1/REFIN2(+)
Figure 18. Basic Connection Diagram
fADC = fCLK/(1024 × FS[9:0])
OVERVIEW
The AD7192 is an ultralow noise ADC that incorporates a Σ-Δ
modulator, a buffer, PGA, and on-chip digital filtering intended
for the measurement of wide dynamic range signals such as
those in pressure transducers, weigh scales, and strain gage
applications.
where:
fADC is the output data rate.
fCLK = master clock (4.92 MHz nominal).
FS[9:0] is the decimal equivalent of Bit FS9 to Bit FS0 in the
mode register.
The part can be configured to have two differential inputs or
four pseudo differential inputs that can be buffered or unbuffered.
Figure 18 shows the basic connections required to operate the part.
The output data rate can be programmed from 4.7 Hz to 4800 Hz;
that is, FS[9:0] can have a value from 1 to 1023.
FILTER, OUTPUT DATA RATE, AND SETTLING TIME
A Σ-Δ ADC consists of a modulator followed by a digital filter.
The AD7192 has two filter options: a sinc3 filter and a sinc4
filter. The filter is selected using the SINC3 bit in the mode
register. When the SINC3 bit is set to 0 (default value), the sinc4
filter is selected. The sinc3 filter is selected when the SINC3 bit is
set to 1.
The previous equation is valid for both the sinc3 and sinc4
filters. The settling time for the sinc4 filter is equal to
tSETTLE = 4/fADC
and the settling time for the sinc3 filter is equal to
tSETTLE = 3/fADC
Figure 19 and Figure 20 show the frequency response of the sinc4
filter and sinc3 filter, respectively, for an output data rate of 50 Hz.
0
At low output data rates (<1 kHz), the noise-free resolution is
comparable for the two filter types. However, at the higher
update rates, the sinc4 filter gives better noise-free resolution.
–10
–20
The sinc filter also leads to better 50 Hz and 60 Hz rejection.
While the notch positions are not affected by the order of the
filter, the higher order filter has wider notches, which leads to
better rejection in the band (±1 Hz) around the notches. It also
gives better stop-band attenuation. The benefit of the sinc3 filter
is its lower settling time for the same output data rate.
FILTER GAIN (dB)
4
–30
–40
–50
–60
–70
–80
Chop Disabled
–100
0
25
50
75
100
125
FREQUENCY (Hz)
Figure 19. Sinc4 Filter Response (50 Hz Output Data Rate)
Rev. A | Page 25 of 40
150
07822-013
–90
The output data rate (the rate at which conversions are available
on a single channel when the ADC is continuously converting)
is equal to
AD7192
0
The value of FS[9:0] can be varied from 1 to 1023. This results
in an output data rate of 1.173 Hz to 1200 Hz for the sinc4 filter
and 1.56 Hz to 1600 Hz for the sinc3 filter. The settling time for
sinc3 or sinc4 is equal to
–10
–30
tSETTLE = 2/fADC
–40
Therefore, with chop enabled, the settling time is reduced for a
given output data rate compared to the chop disabled mode.
However, for a given FS[9:0] value, the output data rate is less
with chop enabled when compared with the chop disabled
mode. For either the sinc3 or sinc4 filter, the cutoff frequency f3dB is
equal to
–50
–60
–70
–80
25
50
75
100
125
150
FREQUENCY (Hz)
Figure 20. Sinc3 Filter Response (50 Hz Output Data Rate)
The sinc4 filter provides 50 Hz (±1 Hz) rejection in excess of
120 dB, assuming a stable master clock, and the sinc3 filter gives
a rejection of 100 dB. The stop-band attenuation is, typically,
53 dB for the sinc4 filter but equal to 40 dB for the sinc3 filter.
f3dB = 0.24 × fADC
Figure 21 and Figure 22 show the filter response for the sinc4
filter and sinc3 filter, respectively, when chop is enabled. As
shown in the plots, the stop-band attenuation is less when
compared with the chop disabled modes.
0
–10
The 3 dB frequency for the sinc4 filter is equal to
–20
FILTER GAIN (dB)
f3dB = 0.23 × fADC
and for the sinc filter, the 3 dB frequency is equal to
f3dB = 0.272 × fADC
Chop Enabled
With chop enabled, the ADC offset and offset drift are
minimized. When chop is enabled, the analog input pins are
continuously swapped. Therefore, with the analog input pins
connected in one direction, the settling time of the sinc filter is
allowed to elapse until a valid conversion is available. The analog
input pins are then inverted, and another valid conversion is
obtained. Subsequent conversions are then averaged so that the
offset is minimized. This continuous swapping of the analog
input pins and the averaging of subsequent conversions means
that the offset drift is also minimized.
Chopping affects the output data rate and settling time of the
ADC. For sinc4, the output data rate is equal to
fADC = fCLK/(4 × 1024 × FS[9:0])
For sinc3, the output data rate is equal to
–40
–50
–60
–80
–90
–100
0
25
50
75
100
125
150
FREQUENCY (Hz)
Figure 21. Sinc4 Filter Response (Output Data Rate =12.5 Hz, Chop Enabled)
0
–10
–20
–30
–40
–50
–60
–70
fADC = fCLK/(3 × 1024 × FS[9:0])
where:
fADC is the output data rate.
fCLK = master clock (4.92 MHz nominal).
FS[9:0] is the decimal equivalent of Bit FS9 to Bit FS0 in the
mode register.
–30
–70
FILTER GAIN (dB)
3
07822-015
0
07822-014
–90
–100
–80
–90
–100
0
25
50
75
100
FREQUENCY (Hz)
125
150
07822-016
FILTER GAIN (dB)
–20
Figure 22. Sinc3 Filter Response (Output Data Rate = 16.6 Hz, Chop Enabled)
Rev. A | Page 26 of 40
AD7192
Normal mode rejection is one of the main functions of the
digital filter. With chop disabled, 50 Hz rejection is obtained
when the output data rate is set to 50 Hz, and 60 Hz rejection is
achieved when the output data rate is set to 60 Hz. Simultaneous 50 Hz and 60 Hz rejection is obtained when the output
data rate is set to 10 Hz. Simultaneous 50 Hz/60 Hz rejection
can also be achieved using the REJ60 bit in the mode register.
When the output data rate is programmed to 50 Hz and the
REJ60 bit is set to 1, notches are placed at both 50 Hz and 60 Hz.
Figure 23 and Figure 24 show the frequency response of the
sinc4 filter and sinc3 filter, respectively, when the output data
rate is programmed to 50 Hz and REJ60 is set to 1.
filter is used. Figure 25 and Figure 26 show the filter response for
both output data rates when REJ60 is set to 1.
0
–10
–20
FILTER GAIN (dB)
50 Hz/60 Hz Rejection
–30
–40
–50
–60
–70
–80
–90
–100
0
–10
25
50
75
100
125
150
FREQUENCY (Hz)
–30
Figure 25. Sinc4 Filter Response (12.5 Hz Output Data Rate,
Chop Enabled, REJ60 = 1)
–40
0
–50
–10
–60
–20
–70
–30
–80
0
25
50
75
100
125
150
FREQUENCY (Hz)
–40
–50
–60
–70
4
Figure 23. Sinc Filter Response (50 Hz Output Data Rate, REJ60=1)
–80
0
–90
–10
–100
0
25
FILTER GAIN (dB)
–20
50
75
100
125
150
FREQUENCY (Hz)
07822-126
–100
07822-017
–90
FILTER GAIN (dB)
FILTER GAIN (dB)
–20
07822-125
0
Figure 26. Sinc3 Filter Response (16.7 Hz Output Data Rate,
Chop Enabled, REJ60 = 1)
–30
–40
Zero Latency
–50
Zero latency is enabled by setting the SINGLE bit in the mode
register to 1. With zero latency, the complete settling time is
allowed for each conversion. Therefore,
–60
–70
–80
fADC = 1/tSETTLE
–100
0
25
50
75
100
125
150
FREQUENCY (Hz)
07822-018
–90
Figure 24. Sinc3 Filter Response (50 Hz Output Data Rate, REJ60=1)
Again, the sinc4 filter provides better 50 Hz/60 Hz rejection
than the sinc3 filter. Also, better stop-band attenuation is
achieved with the sinc4 filter.
When chop is enabled, lower output data rates must be used to
achieve 50 Hz and 60 Hz rejection. With REJ60 set to 1, an output
data rate of 12.5 Hz gives simultaneous 50 Hz/60 Hz rejection
when the sinc4 filter is selected, whereas an output data rate of
16.7 Hz gives simultaneous 50 Hz/60 Hz rejection when the sinc3
Zero latency means that the output data rate is constant
irrespective of the number of analog input channels enabled;
the user does not need to consider the effects of channel
changes on the output data rate. The disadvantages of zero
latency are the increased noise for a given output data rate
compared with the nonzero latency mode. For example, when
zero latency is not enabled, the AD7192 has a noise-free
resolution of 18.5 bits when the output data rate is 50 Hz and
the gain is set to 128. When zero latency is enabled, the ADC
has a resolution of 17.5 bits peak-to-peak when the output data
rate is 50 Hz. The filter response also changes. Figure 19 shows
the filter response for the sinc4 filter when the output data rate
is 50 Hz (zero latency disabled). Figure 27 shows the filter
response when zero latency is enabled and the output data rate
Rev. A | Page 27 of 40
AD7192
is 50 Hz (sinc4 filter); 50 Hz rejection is no longer achieved. The
ADC must operate with an output data rate of 12.5 Hz to obtain
50 Hz rejection when zero latency is enabled. To obtain
simultaneous 50 Hz/60 Hz rejection, the REJ60 bit in the mode
register can be set when the output data rate is equal to 12.5 Hz.
The stop-band attenuation is considerably reduced also (3 dB
compared with 53 dB in the nonzero latency mode).
For example, if the sinc4 filter is selected, chop is disabled, and
zero latency is disabled, the settling time for each channel is
equal to
tSETTLE = 4/fADC
where fADC is the output data rate when continuously converting
on a single channel. The time required to sample N channels is
4/(fADC × N)
0
–10
RDY
–20
CHANNEL A
–40
CHANNEL B
1/fADC
CHANNEL C
07822-019
FILTER GAIN (dB)
CONVERSIONS
–30
Figure 28. Channel Sequencer
–50
–60
DIGITAL INTERFACE
–70
As indicated in the On-Chip Registers section, the programmable functions of the AD7192 are controlled using a set of
on-chip registers. Data is written to these registers via the serial
interface of the part. Read access to the on-chip registers is also
provided by this interface. All communication with the part must
start with a write to the communications register. After power-on
or reset, the device expects a write to its communications register.
The data written to this register determines whether the next operation is a read operation or a write operation and also determines
to which register this read or write operation occurs. Therefore,
write access to any of the other registers on the part begins with a
write operation to the communications register, followed by a
write to the selected register. A read operation from any other
register (except when continuous read mode is selected) starts
with a write to the communications register, followed by a read
operation from the selected register.
–80
0
50
100 150 200 250 300 350 400 450 500 550 600
FREQUENCY (Hz)
07822-020
–90
–100
Figure 27. Sinc4 Filter Response (50 Hz Output Data Rate, Zero Latency)
Channel Sequencer
The AD7192 includes a channel sequencer, which simplifies
communications with the device in multichannel applications.
The sequencer also optimizes the channel throughput of the
device because the sequencer switches channels at the optimum
rate rather than waiting for instructions via the SPI interface.
Bit CH0 to Bit CH7 in the configuration register are used to
enable the required channels. In continuous conversion mode,
the ADC selects each of the enabled channels in sequence and
performs a conversion on the channel. The RDY pin goes low
when a valid conversion is available on each channel. When
several channels are enabled, the contents of the status register
should be attached to the 24-bit word so that the user can
identify the channel that corresponds to each conversion. To
attach the status register value to the conversion, Bit DAT_STA
in the mode register should be set to 1.
When several channels are enabled, the ADC must allow the
complete settling time to generate a valid conversion each time
that the channel is changed. The AD7192 takes care of this:
when a channel is selected, the modulator and filter are reset
and the RDY pin is taken high. The AD7192 then allows the
complete settling time to generate the first conversion. RDY
goes low only when a valid conversion is available. The AD7192
then selects the next enabled channel and converts on that
channel. The user can then read the data register while the
ADC is performing the conversion on the next channel.
The time required to read a valid conversion from all enabled
channels is equal to
tSETTLE × number of enabled channels
The serial interface of the AD7192 consists of four signals: CS,
DIN, SCLK, and DOUT/RDY. The DIN line is used to transfer
data into the on-chip registers, and DOUT/RDY is used for
accessing data from the on-chip registers. SCLK is the serial clock
input for the device, and all data transfers (either on DIN or
DOUT/RDY) occur with respect to the SCLK signal.
The DOUT/RDY pin functions as a data ready signal also, the
line going low when a new data-word is available in the output
register. It is reset high when a read operation from the data
register is complete. It also goes high prior to the updating of the
data register to indicate when not to read from the device, to
ensure that a data read is not attempted while the register is being
updated. CS is used to select a device. It can be used to decode the
AD7192 in systems where several components are connected to
the serial bus.
Figure 3 and Figure 4 show timing diagrams for interfacing to the
AD7192, with CS being used to decode the part. Figure 3 shows
the timing for a read operation from the output shift register of
the AD7192, and Figure 4 shows the timing for a write operation
to the input shift register. It is possible to read the same word
from the data register several times even though the DOUT/RDY
Rev. A | Page 28 of 40
AD7192
line returns high after the first read operation. However, care
must be taken to ensure that the read operations are completed
before the next output update occurs. In continuous read mode,
the data register can be read only once.
The serial interface can operate in 3-wire mode by tying CS low.
In this case, the SCLK, DIN, and DOUT/RDY lines are used to
communicate with the AD7192. The end of the conversion can be
monitored using the RDY bit or pin. This scheme is suitable for
interfacing to microcontrollers. If CS is required as a decoding
signal, it can be generated from a port pin. For microcontroller
interfaces, it is recommended that SCLK idle high between data
transfers.
The AD7192 can be operated with CS used as a frame synchronization signal. This scheme is useful for DSP interfaces. In this
case, the first bit (MSB) is effectively clocked out by CS because
CS normally occurs after the falling edge of SCLK in DSPs. The
SCLK can continue to run between data transfers, provided the
timing numbers are obeyed.
The serial interface can be reset by writing a series of 1s to the
DIN input. If a Logic 1 is written to the AD7192 DIN line for at
least 40 serial clock cycles, the serial interface is reset. This
ensures that the interface can be reset to a known state if the
interface gets lost due to a software error or some glitch in the
system. Reset returns the interface to the state in which it expects
a write to the communications register. This operation resets the
contents of all registers to their power-on values. Following a
reset, the user should allow a period of 500 μs before addressing
the serial interface.
The AD7192 can be configured to continuously convert or to
perform a single conversion (see Figure 29 through Figure 31).
Single Conversion Mode
In single conversion mode, the AD7192 is placed in powerdown mode after conversions. When a single conversion is
initiated by setting MD2, MD1, and MD0 to 0, 0, 1, respectively,
in the mode register, the AD7192 powers up, performs a single
conversion, and then returns to power-down mode. The onchip oscillator requires 1 ms, approximately, to power up.
DOUT/RDY goes low to indicate the completion of a conversion. When the data-word has been read from the data register,
DOUT/RDY goes high. If CS is low, DOUT/RDY remains high
until another conversion is initiated and completed. The data
register can be read several times, if required, even when
DOUT/RDY has gone high.
If several channels are enabled, the ADC sequences through the
enabled channels and performs a conversion on each channel.
When a conversion is started, DOUT/RDY goes high and
remains high until a valid conversion is available. As soon as the
conversion is available, DOUT/RDY goes low. The ADC then
selects the next channel and begins a conversion. The user can
read the present conversion while the next conversion is being
performed. As soon as the next conversion is complete, the data
register is updated; therefore, the user has a limited period in
which to read the conversion. When the ADC has performed a
single conversion on each of the selected channels, it returns to
power-down mode.
If the DAT_STA bit in the mode register is set to 1, the contents
of the status register are output along with the conversion each
time that the data read is performed. The four LSBs of the status
register indicate the channel to which the conversion corresponds.
CS
0x08
0x280060
0x58
DIN
DATA
07822-021
DOUT/RDY
SCLK
Figure 29. Single Conversion
Rev. A | Page 29 of 40
AD7192
Continuous Conversion Mode
Continuous conversion is the default power-up mode. The
AD7192 converts continuously, and the RDY bit in the status
register goes low each time a conversion is complete. If CS is
low, the DOUT/RDY line also goes low when a conversion is
completed. To read a conversion, the user writes to the
communications register, indicating that the next operation is a
read of the data register. When the data-word has been read
from the data register, DOUT/RDY goes high. The user can
read this register additional times, if required. However, the
user must ensure that the data register is not being accessed at
the completion of the next conversion or else the new conversion
word is lost.
When several channels are enabled, the ADC continuously
loops through the enabled channels, performing one conversion
on each channel per loop. The data register is updated as soon
as each conversion is available. The DOUT/RDY pin pulses low
each time a conversion is available. The user can then read the
conversion while the ADC converts on the next enabled channel.
If the DAT_STA bit in the mode register is set to 1, the contents
of the status register are output along with the conversion each
time that the data read is performed. The status register
indicates the channel to which the conversion corresponds.
CS
0x58
0x58
DIN
DATA
DATA
07822-022
DOUT/RDY
SCLK
Figure 30. Continuous Conversion
Rev. A | Page 30 of 40
AD7192
Continuous Read
conversion is complete, and the new conversion is placed in
the output serial register.
Rather than write to the communications register each time a
conversion is complete to access the data, the AD7192 can be
configured so that the conversions are placed on the DOUT/
RDY line automatically. By writing 01011100 to the communications register, the user need only apply the appropriate
number of SCLK cycles to the ADC, and the conversion word
is automatically placed on the DOUT/RDY line when a
conversion is complete. The ADC should be configured for
continuous conversion mode.
To exit the continuous read mode, the Instruction 01011000
must be written to the communications register while the
RDY pin is low. While in the continuous read mode, the ADC
monitors activity on the DIN line so that it can receive the
instruction to exit the continuous read mode. Additionally, a
reset occurs if 40 consecutive 1s are seen on DIN. Therefore,
DIN should be held low in continuous read mode until an
instruction is to be written to the device.
When several channels are enabled, the ADC continuously
steps through the enabled channels and performs one conversion on each channel each time that it is selected. DOUT/
RDY pulses low when a conversion is available. When the user
applies sufficient SCLK pulses, the data is automatically placed
on the DOUT/RDY pin. If the DAT_STA bit in the mode
register is set to 1, the contents of the status register are output
along with the conversion. The status register indicates the
channel to which the conversion corresponds.
When DOUT/RDY goes low to indicate the end of a conversion,
sufficient SCLK cycles must be applied to the ADC; the data
conversion is then placed on the DOUT/RDY line. When the
conversion is read, DOUT/RDY returns high until the next
conversion is available. In this mode, the data can be read only
once. Also, the user must ensure that the data-word is read
before the next conversion is complete. If the user has not read
the conversion before the completion of the next conversion,
or if insufficient serial clocks are applied to the AD7192 to
read the word, the serial output register is reset when the next
CS
0x5C
DIN
DATA
DATA
DATA
07822-023
DOUT/RDY
SCLK
Figure 31. Continuous Read
Rev. A | Page 31 of 40
AD7192
CIRCUIT DESCRIPTION
ANALOG INPUT CHANNEL
The AD7192 has two differential/four pseudodifferential analog
input channels, which can be buffered or unbuffered. In buffered
mode (the BUF bit in the configuration register is set to 1), the
input channel feeds into a high impedance input stage of the
buffer amplifier. Therefore, the input can tolerate significant
source impedances and is tailored for direct connection to
external resistive-type sensors such as strain gages or resistance
temperature detectors (RTDs).
When BUF = 0, the part is operated in unbuffered mode. This
results in a higher analog input current. Note that this unbuffered
input path provides a dynamic load to the driving source.
Therefore, resistor/capacitor combinations on the input pins
can cause gain errors, depending on the output impedance of
the source that is driving the ADC input. Table 22 shows the
allowable external resistance/capacitance values for unbuffered
mode at a gain of 1 such that no gain error at the 20-bit level is
introduced.
Table 22. External R-C Combination for No 20-Bit Gain Error
C (pF)
R (Ω)
50
1.4 k
100
850
500
300
1000
230
5000
30
The absolute input voltage range in buffered mode is restricted
to a range between AGND + 250 mV and AVDD − 250 mV. Care
must be taken in setting up the common-mode voltage so that
these limits are not exceeded. Otherwise, there is degradation in
linearity and noise performance.
The absolute input voltage in unbuffered mode includes the
range between AGND − 50 mV and AVDD + 50 mV. The
negative absolute input voltage limit does allow the possibility
of monitoring small true bipolar signals with respect to AGND.
PROGRAMMABLE GAIN ARRAY (PGA)
When the gain stage is enabled, the output from the buffer is
applied to the input of the PGA. The presence of the PGA
means that signals of small amplitude can be gained within the
AD7192 while still maintaining excellent noise performance.
For example, when the gain is set to 128, the rms noise is 11 nV,
typically, when the output data rate is 4.7 Hz, which is equivalent
to 22.5 bits of effective resolution or 20 bits of noise-free
resolution.
The AD7192 can be programmed to have a gain of 1, 8, 16, 32,
64, and 128 using Bit G2 to Bit G0 in the configuration register.
Therefore, with an external 2.5 V reference, the unipolar ranges
are from 0 mV to 19.53 mV to 0 V to 2.5 V and the bipolar
ranges are from ±19.53 mV to ±2.5 V.
The analog input range must be limited to ±(AVDD – 1.25 V)/gain
because the PGA requires some headroom. Therefore, if AVDD =
5 V, the maximum analog input that can be applied to the
AD7192 is 0 to 3.75 V/gain in unipolar mode or ±3.75 V/gain
in bipolar mode.
BIPOLAR/UNIPOLAR CONFIGURATION
The analog input to the AD7192 can accept either unipolar or
bipolar input voltage ranges. A bipolar input range does not
imply that the part can tolerate negative voltages with respect to
system AGND. In pseudo-differential mode, signals are
referenced to AINCOM, while in differential mode, signals are
referenced to the negative input of the differential pair. For
example, if AINCOM is 2.5 V and the AD7192 AIN1 analog
input is configured for unipolar mode with a gain of 2, the input
voltage range on the AIN1 pin is 2.5 V to 3.75 V when a 2.5 V
reference is used.
If AINCOM is 2.5 V and the AD7192 AIN1 analog input is
configured for bipolar mode with a gain of 2, the analog input
range on AIN1 is 1.25 V to 3.75 V The bipolar/unipolar option
is chosen by programming the U/B bit in the configuration
register.
DATA OUTPUT CODING
When the ADC is configured for unipolar operation, the output
code is natural (straight) binary with a zero differential input
voltage resulting in a code of 00...00, a midscale voltage resulting in a code of 100...000, and a full-scale input voltage resulting
in a code of 111...111. The output code for any analog input
voltage can be represented as
Code = (2N × AIN × Gain)/VREF
When the ADC is configured for bipolar operation, the output
code is offset binary with a negative full-scale voltage resulting
in a code of 000...000, a zero differential input voltage resulting
in a code of 100...000, and a positive full-scale input voltage
resulting in a code of 111...111. The output code for any analog
input voltage can be represented as
Code = 2N – 1 × [(AIN × Gain/VREF) + 1]
where AIN is the analog input voltage, Gain is the PGA setting
(1 to 128), and N = 24.
CLOCK
The AD7192 includes an internal 4.92 MHz clock on-chip. This
internal clock has a tolerance of ±4%. Either the internal clock
or an external crystal/clock can be used as the clock source to
the AD7192. The clock source is selected using the CLK1 and
CLK0 bits in the mode register. When an external crystal is
used, it must be connected across the MCLK1 and MCLK2
pins. The crystal manufacturer recommends the load capacitances
required for the crystal. The MCLK1 and MCLK2 pins of the
AD7192 have a capacitance of 15 pF, typically. If an external
Rev. A | Page 32 of 40
AD7192
BURNOUT CURRENTS
The common-mode range for these differential inputs is from
AGND to AVDD. The reference input is unbuffered; therefore,
excessive R-C source impedances introduce gain errors. The
reference voltage REFIN (REFINx(+) − REFINx(−)) is AVDD
nominal, but the AD7192 is functional with reference voltages
from 1 V to AVDD. In applications where the excitation (voltage
or current) for the transducer on the analog input also drives
the reference voltage for the part, the effect of the low frequency
noise in the excitation source is removed because the application is
ratiometric. If the AD7192 is used in a nonratiometric application, a low noise reference should be used.
The AD7192 contains two 500 nA constant current generators,
one sourcing current from AVDD to AIN(+) and one sinking
current from AIN(−) to AGND, where AIN(+) is the positive
analog input terminal and AIN(−) is the negative analog input
terminal in differential mode and AINCOM in pseudodifferential mode. The currents are switched to the selected analog
input pair. Both currents are either on or off, depending on the
burnout current enable (BURN) bit in the configuration
register.
Recommended 2.5 V reference voltage sources for the AD7192
include the ADR421 and ADR431, which are low noise
references. These references have low output impedances and
are, therefore, tolerant to having decoupling capacitors on
REFINx(+) without introducing gain errors in the system.
Deriving the reference input voltage across an external resistor
means that the reference input sees a significant external source
impedance. External decoupling on the REFINx pins is not
recommended in this type of circuit configuration.
These currents can be used to verify that an external transducer
is still operational before attempting to take measurements on
that channel. After the burnout currents are turned on, they
flow in the external transducer circuit, and a measurement of
the input voltage on the analog input channel can be taken. It
takes some time for the burnout currents to detect an open
circuit condition because the currents must charge any external
capacitors.
REFERENCE DETECT
clock source is used, the clock source must be connected to the
MCLK2 pin, and the MCLK1 pin can be left floating.
The internal clock can also be made available at the MCLK2
pin. This is useful when several ADCs are used in an application
and the devices must be synchronized. The internal clock from
one device can be used as the clock source for all ADCs in the
system. Using a common clock, the devices can be synchronized by applying a common reset to all devices, or the SYNC
pin can be pulsed.
There are several reasons that a fault condition is detected. The
front-end sensor may be open circuit. It could also mean that
the front-end sensor is overloaded or the reference may be
absent and the NOREF bit in the status register is set, thus
clamping the data to all 1s.
The user must check these three cases before making a judgment.
If the voltage measured is 0 V, it may indicate that the
transducer has short circuited. The current sources work over
the normal absolute input voltage range specifications when the
analog inputs are buffered and chop is disabled.
REFERENCE
The ADC has a fully differential input capability for the
reference channel. In addition, the user has the option of
selecting one of two external reference options (REFIN1(x) or
REFIN2(x)). The reference source for the AD7192 is selected
using the REFSEL bit in the configuration register. The
REFIN2(x) pins are dual purpose: they can function as two
general-purpose output pins or as reference pins. When the
REFSEL bit is set to 1, these pins automatically function as
reference pins.
The AD7192 includes on-chip circuitry to detect whether the
part has a valid reference for conversions or calibrations. This
feature is enabled when the REFDET bit in the configuration
register is set to 1. If the voltage between the selected REFINx(+)
and REFINx(−) pins is between 0.3 V and 0.6 V, the AD7192
detects that it no longer has a valid reference. In this case, the
NOREF bit of the status register is set to 1. If the AD7192 is
performing normal conversions and the NOREF bit becomes
active, the conversion result is all 1s.
Therefore, it is not necessary to continuously monitor the status
of the NOREF bit when performing conversions. It is only
necessary to verify its status if the conversion result read from
the ADC data register is all 1s. If the AD7192 is performing
either an offset or full-scale calibration and the NOREF bit
becomes active, the updating of the respective calibration
registers is inhibited to avoid loading incorrect coefficients to
these registers, and the ERR bit in the status register is set. If the
user is concerned about verifying that a valid reference is in
place every time a calibration is performed, the status of the
ERR bit should be checked at the end of the calibration cycle.
Rev. A | Page 33 of 40
AD7192
RESET
TEMPERATURE SENSOR
The circuitry and serial interface of the AD7192 can be reset by
writing consecutive 1s to the device; 40 consecutive 1s are
required to perform the reset. This resets the logic, the digital
filter, and the analog modulator, whereas all on-chip registers
are reset to their default values. A reset is automatically
performed on power-up. When a reset is initiated, the user
must allow a period of 500 μs before accessing any of the onchip registers. A reset is useful if the serial interface loses
synchronization due to noise on the SCLK line.
Embedded in the AD7192 is a temperature sensor. This is
selected using the CH2 bit in the configuration register. When
the CH2 bit is set to 1, the temperature sensor is enabled. When
the temperature sensor is selected and bipolar mode is selected,
the device should return a code of 0x800000 when the temperature is 0 K. A one-point calibration is needed to get the optimum
performance from the sensor. Therefore, a conversion at 25°C
should be recorded and the sensitivity calculated. The sensitivity
is 2815 codes/°C, approximately. The equation for the temperature sensor is
SYSTEM SYNCHRONIZATION
The SYNC input allows the user to reset the modulator and the
digital filter without affecting any of the setup conditions on the
part. This allows the user to start gathering samples of the
analog input from a known point in time, that is, the rising edge
of SYNC. SYNC needs to be taken low for at least four master
clock cycles to implement the synchronization function.
If multiple AD7192 devices are operated from a common master
clock, they can be synchronized so that their data registers are
updated simultaneously. A falling edge on the SYNC pin resets
the digital filter and the analog modulator and places the AD7192
into a consistent, known state. While the SYNC pin is low, the
AD7192 is maintained in this state. On the SYNC rising edge,
the modulator and filter are taken out of this reset state and, on
the next clock edge, the part starts to gather input samples again.
In a system using multiple AD7192 devices, a common signal to
their SYNC pins synchronizes their operation. This is normally
done after each AD7192 has performed its own calibration or
has calibration coefficients loaded into its calibration registers.
The conversions from the AD7192s are then synchronized.
The part is taken out of reset on the master clock falling edge
following the SYNC low to high transition. Therefore, when
multiple devices are being synchronized, the SYNC pin should
be taken high on the master clock rising edge to ensure that all
devices begin sampling on the master clock falling edge. If the
SYNC pin is not taken high in sufficient time, it is possible to
have a difference of one master clock cycle between the devices;
that is, the instant at which conversions are available differs
from part to part by a maximum of one master clock cycle.
The SYNC pin can also be used as a start conversion command.
In this mode, the rising edge of SYNC starts conversion, and the
falling edge of RDY indicates when the conversion is complete.
The settling time of the filter has to be allowed for each data
register update. For example, if the ADC is configured to use
the sinc4 filter, zero latency is disabled, and chop is disabled, the
settling time equals 4/fADC where fADC is the output data rate
when continuously converting on a single channel.
Temp (K) = (Conversion – 0x800000)/2815 K
Temp (°C) = Temp (K) – 273
Following the one-point calibration, the internal temperature
sensor has an accuracy of ±2 °C, typically.
BRIDGE POWER-DOWN SWITCH
In bridge applications such as strain gages and load cells, the
bridge itself consumes the majority of the current in the system.
For example, a 350 Ω load cell requires 15 mA of current when
excited with a 5 V supply. To minimize the current consumption
of the system, the bridge can be disconnected (when it is not
being used) using the bridge power-down switch. Figure 18
shows how the bridge power-down switch is used. The switch
can withstand 30 mA of continuous current, and it has an on
resistance of 11 Ω maximum.
LOGIC OUTPUTS
The AD7192 has four general-purpose digital outputs, P0, P1,
P2, and P3. These are enabled using the GP32EN and GP10EN
bits in the GPOCON register. The pins can be pulled high or
low using the P0DAT to P3DAT bits in the GPOCON register;
that is, the value at the pin is determined by the setting of the
P0DAT to P3DAT bits. The logic levels for these pins are
determined by AVDD rather than by DVDD. When the GPOCON
register is read, Bit P0DAT to Bit P3DAT reflect the actual value
at the pins. This is useful for short-circuit detection.
These pins can be used to drive external circuitry, for example,
an external multiplexer. If an external multiplexer is used to
increase the channel count, the multiplexer logic pins can be
controlled via the AD7192 general-purpose output pins. The
general-purpose output pins can be used to select the active
multiplexer pin. Because the operation of the multiplexer is
independent of the AD7192, the AD7192 modulator and filter
should be reset using the SYNC pin or by a write to the mode or
configuration register each time that the multiplexer channel is
changed.
Rev. A | Page 34 of 40
AD7192
ENABLE PARITY
The AD7192 also has a parity check function on chip that
detects 1-bit errors in the serial communications between the
ADC and the microprocessor. When the ENPAR bit in the
mode register is set to 1, parity is enabled. The contents of the
status register must be transmitted along with each 24-bit conversion when the parity function is enabled. To append the
contents of the status register to each conversion read, the
DAT_STA bit in the mode register should be set to 1. For each
conversion read, the parity bit in the status register is programmed so that the overall number of 1s transmitted in the
24-bit data-word is even. Therefore, for example, if the 24-bit
conversion contains eleven 1s (binary format), the parity bit is
set to 1 so that the total number of 1s in the serial transmission
is even. If the microprocessor receives an odd number of 1s, it
knows that the data received has been corrupted.
The parity function detects only 1-bit errors. For example, two
bits of corrupt data can result in the microprocessor receiving an
even number of 1s. Therefore, an error condition is not detected.
CALIBRATION
The AD7192 provides four calibration modes that can be programmed via the mode bits in the mode register. These modes
are internal zero-scale calibration, internal full-scale calibration,
system zero-scale calibration, and system full-scale calibration.
A calibration can be performed at any time by setting the MD2
to MD0 bits in the mode register appropriately. A calibration
should be performed when the gain is changed. After each
conversion, the ADC conversion result is scaled using the ADC
calibration registers before being written to the data register.
The offset calibration coefficient is subtracted from the result
prior to multiplication by the full-scale coefficient.
To start a calibration, write the relevant value to the MD2 to
MD0 bits. The DOUT/RDY pin and the RDY bit in the status
register go high when the calibration is initiated. When the
calibration is complete, the contents of the corresponding
calibration registers are updated, the RDY bit in the status
register is reset, the DOUT/RDY pin returns low (if CS is low),
and the AD7192 reverts to idle mode.
During an internal zero-scale or full-scale calibration, the
respective zero input and full-scale input are automatically
connected internally to the ADC input pins. A system
calibration, however, expects the system zero-scale and system
full-scale voltages to be applied to the ADC pins before
initiating the calibration mode. In this way, errors external to
the ADC are removed.
From an operational point of view, treat a calibration like
another ADC conversion. A zero-scale calibration, if required,
must always be performed before a full-scale calibration. Set the
system software to monitor the RDY bit in the status register or
the DOUT/RDY pin to determine the end of calibration via a
polling sequence or an interrupt-driven routine.
With chop disabled, both an internal zero-scale calibration and
a system zero-scale calibration require a time equal to the
settling time, tSETTLE (4/fADC for the sinc4 filter and 3/fADC for the
sinc3 filter).
With chop enabled, an internal zero-scale calibration is not
needed because the ADC itself minimizes the offset continuously.
However, if an internal zero-scale calibration is performed, the
settling time, tSETTLE (2/fADC), is required to perform the
calibration. Similarly, a system zero-scale calibration requires a
time of tSETTLE to complete.
To perform an internal full-scale calibration, a full-scale input
voltage is automatically connected to the selected analog input
for this calibration. For a gain of 1, the time required for an
internal full-scale calibration is equal to tSETTLE. For higher gains,
the internal full-scale calibration requires a time of 2 × tSETTLE.
A full-scale calibration is recommended each time the gain of a
channel is changed to minimize the full-scale error.
A system full-scale calibration requires a time of tSETTLE. With
chop disabled, the zero-scale calibration (internal or system
zero-scale) should be performed before the system full-scale
calibration is initiated.
An internal zero-scale calibration, system zero-scale calibration,
and system full-scale calibration can be performed at any
output data rate. An internal full-scale calibration can be
performed at any output data rate for which the filter word,
FS[9:0], is divisible by 16, FS[9:0] being the decimal equivalent
of the 10-bit word written to Bit FS9 to Bit FS0 in the mode
register. Therefore, internal full-scale calibrations can be
performed at output data rates such as 10 Hz or 50 Hz when
chop is disabled. Using these lower output data rates results in
better calibration accuracy.
The offset error is, typically, 150 μV/gain. If the gain is changed,
it is advisable to perform a calibration. A zero-scale calibration
(an internal zero-scale calibration or a system zero-scale
calibration) reduces the offset error to the order of the noise.
The gain error of the AD7192 is factory calibrated at a gain of 1
with a 5 V power supply at ambient temperature. Following this
calibration, the gain error is 0.001%, typically, at 5 V. Table 23
shows the typical uncalibrated gain error for the different gain
settings.
Table 23. Typical Precalibration Gain Error vs. Gain
Gain
8
16
32
64
128
Precalibration Gain Error (%)
−0.11
−0.20
−0.23
−0.29
−0.39
An internal full-scale calibration reduces the gain error to
0.001%, typically, when the gain is equal to 1. For higher gains,
the gain error post internal full-scale calibration is 0.003%,
typically when AVDD is equal to 5 V. When AVDD is less than
Rev. A | Page 35 of 40
AD7192
4.75 V, the gain error post internal full-scale calibration is
0.005%, typically.
etch technique is generally best for ground planes because it
gives the best shielding.
When AVDD is less than 4.75 V, the CLK_DIV bit must be set
when performing internal full-scale calibrations. The accuracy
of the internal full-scale calibration is further increased if chop
is enabled and a low output data rate is used while performing
the calibration.
Although the AD7192 has separate pins for analog and digital
ground, the AGND and DGND pins are tied together internally
via the substrate. Therefore, the user must not tie these two
pins to separate ground planes unless the ground planes are
connected together near the AD7192.
A system full-scale calibration reduces the gain error to the
order of the noise irrespective of the analog power supply
voltage.
In systems in which the AGND and DGND are connected
somewhere else in the system (that is, the power supply of the
system), they should not be connected again at the AD7192
because a ground loop results. In these situations, it is
recommended that the ground pins of the AD7192 be tied to
the AGND plane.
The AD7192 gives the user access to the on-chip calibration
registers, allowing the microprocessor to read the calibration
coefficients of the device and also to write its own calibration
coefficients from prestored values in the EEPROM. A read of
the registers can be performed at any time. However, the ADC
must be placed in power-down or idle mode when writing to
the registers. The values in the calibration registers are 24 bits
wide. The span and offset of the part can also be manipulated
using the registers.
GROUNDING AND LAYOUT
Because the analog inputs and reference inputs are differential,
most of the voltages in the analog modulator are commonmode voltages. The high common-mode rejection of the part
removes common-mode noise on these inputs. The analog and
digital supplies to the AD7192 are independent and separately
pinned out to minimize coupling between the analog and
digital sections of the device. The digital filter provides
rejection of broadband noise on the power supplies, except at
integer multiples of the modulator sampling frequency.
Connect an R-C filter to each analog input pin to provide
rejection at the modulator sampling frequency. A 100 Ω
resistor in series with each analog input, a 0.1 μF capacitor
between the analog input pins, and a 0.01 μF capacitor from
each analog input to AGND are advised.
The digital filter also removes noise from the analog and
reference inputs provided that these noise sources do not
saturate the analog modulator. As a result, the AD7192 is
more immune to noise interference than a conventional high
resolution converter. However, because the resolution of the
AD7192 is so high and the noise levels from the converter so
low, care must be taken with regard to grounding and layout.
The printed circuit board (PCB) that houses the ADC must be
designed so that the analog and digital sections are separated
and confined to certain areas of the board. This facilitates the
use of ground planes that can be easily separated. A minimum
In any layout, the user must keep in mind the flow of currents
in the system, ensuring that the paths for all currents are as close as
possible to the paths the currents took to reach their destinations.
Avoid forcing digital currents to flow through the AGND.
Avoid running digital lines under the device, because this
couples noise onto the die, and allow the analog ground plane
to run under the AD7192 to prevent noise coupling. The power
supply lines to the AD7192 must use as wide a trace as possible
to provide low impedance paths and reduce the effects of
glitches on the power supply line. Shield fast switching signals
like clocks with digital ground to prevent radiating noise to
other sections of the board, and never run clock signals near the
analog inputs. Avoid crossover of digital and analog signals.
Run traces on opposite sides of the board at right angles to each
other. This reduces the effects of feedthrough through the
board. A microstrip technique is by far the best but is not
always possible with a double-sided board. In this technique,
the component side of the board is dedicated to ground planes,
whereas signals are placed on the solder side.
Good decoupling is important when using high resolution
ADCs. Decouple all analog supplies with 10 μF tantalum
capacitors in parallel with 0.1 μF capacitors to AGND. To
achieve the best results from these decoupling components,
place them as close as possible to the device, ideally right up
against the device. Decouple all logic chips with 0.1 μF ceramic
capacitors to DGND. In systems in which a common supply
voltage is used to drive both the AVDD and DVDD of the
AD7192, it is recommended that the system AVDD supply be
used. For this supply, place the recommended analog supply
decoupling capacitors between the AVDD pin of the AD7192
and AGND and the recommended digital supply decoupling
capacitor between the DVDD pin of the AD7192 and DGND.
Rev. A | Page 36 of 40
AD7192
APPLICATIONS INFORMATION
measurements can be taken. In applications in which current
consumption is being minimized, the AD7192 can be placed in
standby mode, thus significantly reducing the power consumed
in the application. In addition, the bridge power-down switch
can be opened while in standby mode, thus avoiding unnecessary
power consumption by the front-end transducer. When the part
is taken out of standby mode and the bridge power-down switch
is closed, the user should ensure that the front end circuitry is
fully settled before attempting a read from the AD7192.
The AD7192 provides a low-cost, high resolution analog-todigital function. Because the analog-to-digital function is
provided by a Σ-Δ architecture, the part is more immune to
noisy environments, making it ideal for use in sensor
measurement and industrial and process control applications.
WEIGH SCALES
Figure 32 shows the AD7192 being used in a weigh scale
application. The load cell is arranged in a bridge network and
gives a differential output voltage between its OUT+ and OUT–
terminals. Assuming a 5 V excitation voltage, the full-scale
output range from the transducer is 10 mV when the sensitivity
is 2 mV/V. The excitation voltage for the bridge can be used to
directly provide the reference for the ADC because the reference
input range includes the supply voltage.
For simplicity, external filters are not included in Figure 32.
However, an R-C antialias filter must be included on each
analog input. This is required because the on-chip digital filter
does not provide any rejection around the modulator sampling
frequency or multiples of this frequency. Suitable values are a
100 Ω resistor in series with each analog input, a 0.1 μF
capacitor between the analog input pins, and a 0.01 μF
capacitor from each analog input pin to AGND.
A second advantage of using the AD7192 in transducer-based
applications is that the bridge power-down switch can be fully
utilized to minimize the power consumption of the system. The
bridge power-down switch is connected in series with the cold
side of the bridge. In normal operation, the switch is closed and
5V
OUT+
OUT–
IN–
AIN1
AIN2
AIN3
AIN4
AINCOM MUX
BPDSW
REFERENCE
DETECT
SERIAL
INTERFACE
AND
CONTROL
LOGIC
Σ-Δ
ADC
PGA
AGND
REFIN1(–)
DVDD DGND
AVDD
AVDD
DOUT/RDY
DIN
SCLK
CS
SYNC
TEMP
SENSOR
AD7192
P3
P2
CLOCK
CIRCUITRY
AGND
MCLK1 MCLK2
P0/REFIN2(–) P1/REFIN2(+)
Figure 32. Typical Application (Weigh Scale)
Rev. A | Page 37 of 40
07822-024
REFIN1(+) AGND
IN+
AD7192
OUTLINE DIMENSIONS
7.90
7.80
7.70
24
13
4.50
4.40
4.30
6.40 BSC
1
12
PIN 1
0.65
BSC
0.15
0.05
0.30
0.19
1.20
MAX
SEATING
PLANE
0.20
0.09
8°
0°
0.75
0.60
0.45
0.10 COPLANARITY
COMPLIANT TO JEDEC STANDARDS MO-153-AD
Figure 33. 24-Lead Thin Shrink Small Outline Package [TSSOP]
(RU-24)
Dimensions shown in millimeters
ORDERING GUIDE
Model
AD7192BRUZ 1
AD7192BRUZ-REEL1
1
Temperature Range
–40°C to +105°C
–40°C to +105°C
Package Description
24-Lead TSSOP
24-Lead TSSOP
Z = RoHS Compliant Part.
Rev. A | Page 38 of 40
Package Option
RU-24
RU-24
AD7192
NOTES
Rev. A | Page 39 of 40
AD7192
NOTES
©2009 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D07822-0-5/09(A)
Rev. A | Page 40 of 40
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