Low Noise, High Throughput
24-Bit Sigma-Delta ADC
a
AD7731
GENERAL D ESCRIP TIO N
FEATURES
T he AD7731 is a complete analog front-end for process control
applications. T he device has a proprietary programmable gain
front end that allows it to accept a range of input signal ranges,
including low level signals, directly from a transducer. The sigma-
delta architecture of the part consists of an analog modulator
and a low pass programmable digital filter, allowing adjustment
of filter cutoff, output rate and settling time.
24-Bit Sigm a-Delta ADC
16 Bits p-p Resolution at 800 Hz Output Rate
Program m able Output Rates up to 6.4 kHz
Program m able Gain Front End
؎0.0015% Nonlinearity
Buffered Differential Inputs
Program m able Filter Cutoffs
FASTStep™* Mode for Channel Sequencing
Single Supply Operation
T he part features three buffered differential programmable gain
analog inputs (which can be configured as five pseudo-differential
inputs), as well as a differential reference input. T he part oper-
ates from a single +5 V supply and accepts seven unipolar ana-
log input ranges: 0 to +20 mV, +40 mV, +80 mV, +160 mV,
+320 mV, +640 mV and +1.28 V, and seven bipolar ranges:
±20 mV, ±40 mV, ±80 mV, ±160 mV, ±320 mV, ±640 mV and
±1.28 V. T he peak-to-peak resolution achievable directly from
the part is 16 bits at an 800 Hz output rate. T he part can switch
between channels with 1 ms settling time and maintain a perfor-
mance level of 13 bits of peak-to-peak resolution.
APPLICATIONS
Process Control
PLCs/ DCS
Industrial Instrum entation
T he serial interface on the part can be configured for three-wire
operation and is compatible with microcontrollers and digital
signal processors. T he AD7731 contains self-calibration and
system calibration options and features an offset drift of less
than 5 nV/°C and a gain drift of less than 2 ppm/°C.
T he part is available in a 24-lead plastic DIP, a 24-lead SOIC
and 24-lead T SSOP package.
FUNCTIO NAL BLO CK D IAGRAM
REF IN(–)
DV
DD
REF IN(+)
AV
DD
AD7731
NC
AIN1
AIN2
AIN3
AIN4
AIN5
AIN6
AV
DD
STANDBY
SYNC
SIGMA-DELTA A/D CONVERTER
100nA
BUFFER
SIGMA-
DELTA
PROGRAMMABLE
DIGITAL
MODULATOR
FILTER
PGA
MUX
100nA
AGND
MCLK IN
CLOCK
GENERATION
SERIAL INTERFACE
MCLK OUT
AND CONTROL LOGIC
REGISTER BANK
SCLK
CS
CALIBRATION
MICROCONTROLLER
DIN
DOUT
AGND
DGND
POL
RDY
RESET
*FASTStep is a trademark of Analog Devices, Inc.
REV. A
REV. 0
Inform ation furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assum ed by Analog Devices for its
use, nor for any infringem ents of patents or other rights of third parties
which m ay result from its use. No license is granted by im plication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norw ood, MA 02062-9106, U.S.A.
Tel: 617/ 329-4700
Fax: 617/ 326-8703
World Wide Web Site: http:/ / w w w .analog.com
© Analog Devices, Inc., 1997