Low Power, 16/24-Bit Sigma-Delta ADC with
Low-Noise In-Amp and Embedded Reference
Preliminary Technical Data
AD7792/AD7793


REV.PrF 6/04.
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FEATURES
Resolution: AD7792: 16-Bit
AD7793: 24-Bit
Low Noise Programmable Gain Instrumentation-Amp
RMS noise: 80 nV (Gain = 64)
Bandgap Reference with 5ppm/ C Drift typ
Power
Supply: 2.7 V to 5.25 V operation
Normal: 400 µA typ
Power-down: 1 µA max
Update Rate: 4 Hz to 500 Hz
Simultaneous 50 Hz/60 Hz Rejection
Internal Clock Oscillator
Programmable Current Sources (10 µA/200 µA/1 mA)
On-Chip Bias Voltage Generator
100 nA Burnout Currents
Independent Interface Power Supply
16-Lead TSSOP Package

INTERFACE
3-wire serial
SPI®, QSPI™, MICROWIRE™, and DSP compatible
Schmitt trigger on SCLK

APPLICATIONS
Thermocouple Measurements
RTD Measurements
Thermistor Measurements

FUNCTIONAL BLOCK DIAGRAM

GND AV
DD
AD7792/AD7793
SERIAL
INTERFACE
AND
CONTROL
LOGIC
INTERNAL
CLOCK
CLK
SIGMA DELTA
ADC
REFIN(+)/AIN3(+)
REFIN(-)/AIN3(-)
BANDGAP
REFERENCE
GND
IN-AMP
V
DD
GND
DOUT/RDY
DIN
SCLK
CS
DVDD
AIN1(+)
AIN1(-)
AIN2(+)
AIN2(-)
V
DD
IOUT2
V
BIAS
IOUT1
MUX

Figure 1.

GENERAL DESCRIPTION
The AD7792/AD7793 is a low power, complete analog front end
for low frequency measurement applications. The
AD7792/AD7793 contains a low noise 16/24-bit ∑-∆ ADC with
three differential analog inputs. The on-chip low noise
instrumentation amplifier means that signals of small
amplitude can be interfaced directly to the ADC. With a gain
setting of 64, the rms noise is 80 nV when the update rate equals
16.6 Hz.
The device contains a precision low noise, low drift internal
bandgap reference for absolute measurements. An external
reference can also be used if ratiometric measurements are re-
quired. On-chip programmable excitation current sources can
be used to supply a constant current to RTDs and thermistors
while the 100 nA burnout currents can be used to ensure that
the sensors connected to the ADC are not burnt out. For ther-
mocouple applications, the on-chip bias voltage generator steps
up the common mode voltage from the thermocouple so that it
is within the ADC’s allowable range.
The device can be operated with the internal clock or, alterna-
tively, an external clock can be used if synchronizing several
devices. The output data rate from the part is software pro-
grammable and can be varied from 4 Hz to 500 Hz.
The part operates with a power supply from 2.7 V to 5.25 V. It
consumes a current of 450 uA maximum and is housed in a 16-
lead TSSOP package.