6-Channel, Low Noise, Low Power, 24-/16-Bit
∑-Δ ADC with On-Chip In-Amp and Reference
AD7794/AD7795
FEATURES
Industrial process control
Instrumentation
Blood analysis
Smart transmitters
Liquid/gas chromatography
6-digit DVM
Up to 23 effective bits
RMS noise: 40 nV @ 4.17 Hz, 85 nV @ 16.7 Hz
Current: 400 μA typical
Power-down: 1 μA maximum
Low noise, programmable gain, instrumentation amp
Band gap reference with 4 ppm/°C drift typical
Update rate: 4.17 Hz to 470 Hz
Six differential analog inputs
Internal clock oscillator
Simultaneous 50 Hz/60 Hz rejection
Reference detect
Programmable current sources
On-chip bias voltage generator
Burnout currents
Low-side power switch
Power supply: 2.7 V to 5.25 V
Temperature range:
B grade: –40°C to +105°C
C grade: –40°C to +125°C
Independent interface power supply
24-lead TSSOP
3-wire serial interface
SPI®, QSPI™, MICROWIRE™, and DSP compatible
Schmitt trigger on SCLK
GENERAL DESCRIPTION
The AD7794/AD7795 are low power, low noise, complete
analog front ends for high precision measurement applications.
They contain a low noise, 24-/16-bit ∑-Δ ADC with six
differential inputs. The on-chip low noise instrumentation
amplifier means that signals of small amplitude can be
interfaced directly to the ADC.
Each device contains a precision, low noise, low drift internal
band gap reference, and can also accept up to two external
differential references. Other on-chip features include
programmable excitation current sources, burnout currents,
and a bias voltage generator that is used to set the commonmode voltage of a channel to AVDD/2. The low-side power
switch can be used to power down bridge sensors between
conversions, minimizing the system’s power consumption. The
AD7794/AD7795 can operate with either an internal clock or
an external clock. The output data rate from each part can vary
from 4.17 Hz to 470 Hz.
Both parts operate with a power supply from 2.7 V to 5.25 V.
The B-grade parts (AD7794 and AD7795) are specified for a
temperature range of −40°C to +105°C while the C-grade part
(AD7794) is specified for a temperature range of −40°C to
+125°C. They consume a current of 400 μA typical and are
housed in a 24-lead TSSOP.
APPLICATIONS
Temperature measurement
Pressure measurement
Weigh scales
Strain gage transducers
Gas analysis
FUNCTIONAL BLOCK DIAGRAM
GND
AVDD
AIN4(+)/REFIN2(+) REFIN1(+) AIN4(–)/REFIN2(–) REFIN1(–)
VBIAS
VDD
AIN1(+)
AIN1(–)
AIN2(+)
AIN2(–)
AIN3(+)
AIN3(–)
AIN5(+)/IOUT2
AIN5(–)/IOUT1
AIN6(+)/P1
AIN6(–)/P2
REFERENCE
DETECT
BAND GAP
REFERENCE
GND
BUF
Σ-Δ
ADC
IN-AMP
MUX
SERIAL
INTERFACE
AND
LOGIC
CONTROL
DOUT/RDY
DIN
SCLK
CS
GND
TEMP
SENSOR
INTERNAL
CLOCK
DVDD
AD7794/AD7795
VDD
PSW
GND
CLK
04854-001
AD7794: 24-BIT ADC
AD7795: 16-BIT ADC
Figure 1.
Rev. D
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