Pin-Programmable, Ultralow Noise, 24-Bit,
Sigma-Delta ADC for Bridge Sensors
AD7191
Rev. A
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FEATURES
Pin-programmable output rate
Output data rate: 10 Hz, 50 Hz, 60 Hz, 120 Hz
Pin-programmable PGA
Gain: 1, 8, 64, 128
Pin-programmable power-down and reset
RMS noise: 15 nV @ 10 Hz (gain = 128)
Up to 21.5 noise free bits (gain = 1)
Internal or external clock
Bridge power-down switch
Offset drift: 5 nV/°C
Gain drift: 1 ppm/°C
Specified drift over time
Simultaneous 50 Hz/60 Hz rejection
Internal temperature sensor
Power supply: 3 V to 5.25 V
Current: 4.35 mA
Temperature range: –40°C to +105°C
Package: 24-lead TSSOP
INTERFACE
2-wire serial
SPI, QSPI, and MICROWIRE compatible
Schmitt trigger on SCLK
APPLICATIONS
Weigh scales
Strain gauge transducers
Pressure measurement
Medical and scientific instrumentation
GENERAL DESCRIPTION
The AD7191 is a low noise, complete analog front end for high
precision measurement applications. It contains a low noise,
24-bit sigma-delta (Σ-Δ) ADC. The on-chip low noise gain
stage means that signals of small amplitude can be interfaced
directly to the ADC. It contains two differential analog inputs.
The part also includes a temperature sensor that can be used for
temperature compensation.
For ease-of-use, all the features of the AD7191 are controlled by
dedicated pins. The on-chip PGA has a gain of 1, 8, 64, or 128,
supporting a full-scale differential input of ±5 V, ±625 mV,
±78 mV, or ±39 mV. The output data rate can be programmed
to 10 Hz, 50 Hz, 60 Hz, or 120 Hz. Simultaneous 50 Hz and 60 Hz
rejection is obtained when the output data rate is set to 10 Hz
or 50 Hz; 60 Hz only rejection is obtained when the output data
rate is set to 60 Hz. The AD7191 can be operated with the
internal clock, or an external clock can be used.
The part operates with a power supply of 3 V to 5.25 V. It
consumes a current of 4.35 mA. It is available in a 24-lead
TSSOP package.
FUNCTIONAL BLOCK DIAGRAM
MUX
AD7191
AIN1
DOUT/RDY
SCLK
PDOWN
CHAN
CLKSEL
PGA2
PGA1
AGND
DGND
REFIN(+) REFIN(–)
AVDD
DVDD
AIN2
AIN3
AIN4
BPDSW
MCLK1
MCLK2
ODR2 ODR1 TEMP
TEMPERATURE
SENSOR
CLOCK
CIRCUITRY
PGA
SERIAL
INTERFACE
AND CONTROL
LOGIC
Σ-Δ
ADC
08
16
3-
0
01
Figure 1.