Low Power, 16-/24-Bit Sigma-Delta ADC
for Bridge Sensors
AD7796/AD7797
GENERAL DESCRIPTION
FEATURES
RMS noise: 65 nV
Instrumentation amp
Temperature sensor
Internal clock oscillator
Simultaneous 50 Hz/60 Hz rejection
Update rate: 4.17 Hz to 123 Hz
Current: 250 μA typ
The AD7796/AD7797 are complete, analog front ends for high
precision, bridge sensor applications such as weigh scales. The
AD7796/AD7797 contain a Σ-Δ ADC capable of 16-/24-bit
resolution, respectively. The on-chip instrumentation amplifier
has a fixed gain of 128, allowing small amplitude signals such as
those from bridge sensors to be directly interfaced to the ADC.
Each part has one differential input and contains a temperature
sensor that is internally connected to the ADC. This sensor can
be used to perform temperature compensation of the bridge.
Power-down: 1 μA
Power supply: 2.7 V to 5.25 V
–40°C to +85°C temperature range
Independent interface power supply
16-lead TSSOP
The devices can be operated with the internal clock or an
external clock. The output data rate from the parts is software-
programmable and can be varied from 4.17 Hz to 123 Hz.
INTERFACE
The AD7796/AD7797 operate with a power supply from 2.7 V
to 5.25 V. Each part consumes a current of 250 μA typical and is
housed in a 16-lead TSSOP.
3-wire serial
SPI®, QSPI™, MICROWIRE™, and DSP compatible
Schmitt trigger on SCLK
APPLICATIONS
Weigh scales
Strain gages
Industrial process control
Instrumentation
Portable instrumentation
FUNCTIONAL BLOCK DIAGRAM
AV
REFIN(+) REFIN(–)
GND
DD
AD7796: 16-BIT ADC
AD7797: 24-BIT ADC
AV
DD
SERIAL
INTERFACE
AND
CONTROL
LOGIC
DOUT/RDY
DIN
SCLK
CS
AIN(+)
AIN(–)
Σ-Δ
ADC
×128
MUX
GND
REFERENCE
DV
DD
INTERNAL
CLOCK
TEMP
SENSOR
AD7796/
AD7797
CLK
Figure 1.
Rev. A
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