FUNCTIONAL BLOCK DIAGRAM
REV. G
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a
Signal Conditioning ADC
AD7710
FEATURES
Charge Balancing ADC
24 Bits, No Missing Codes
ⴞ0.0015% Nonlinearity
2-Channel Programmable Gain Front End
Gains from 1 to 128
Differential Inputs
Low-Pass Filter with Programmable Filter Cutoffs
Ability to Read/Write Calibration Coefficients
Bidirectional Microcontroller Serial Interface
Internal/External Reference Option
Single- or Dual-Supply Operation
Low Power (25 mW Typ) with Power-Down Mode
(7 mW Typ)
APPLICATIONS
Weigh Scales
Thermocouples
Process Control
Smart Transmitters
Chromatography
GENERAL DESCRIPTION
The AD7710 is a complete analog front end for low frequency
measurement applications. The device accepts low level signals
directly from a strain gage or transducer and outputs a serial
digital word. It employs a sigma-delta conversion technique to
realize up to 24 bits of no missing codes performance. The input
signal is applied to a proprietary programmable gain front end
based around an analog modulator. The modulator output is
processed by an on-chip digital filter. The first notch of this
digital filter can be programmed via the on-chip control register,
allowing adjustment of the filter cutoff and settling time.
The part features two differential analog inputs and a differen-
tial reference input. Typically, one of the channels will be used
as the main channel with the second channel used as an auxil-
iary input to measure a second voltage periodically. It can be
operated from a single supply (by tying the V
SS
pin to AGND),
provided that the input signals on the analog inputs are more
positive than –30 mV. By taking the V
SS
pin negative, the part
can convert signals down to –V
REF
on its inputs. The AD7710
thus performs all signal conditioning and conversion for a single-
or dual-channel system.
The AD7710 is ideal for use in smart, microcontroller based
systems. Input channel selection, gain settings, and signal polar-
ity can be configured in software using the bidirectional serial
port. The AD7710 contains self-calibration, system calibration,
and background calibration options, and also allows the user to
read and write the on-chip calibration registers.
CMOS construction ensures low power dissipation, and a soft-
ware programmable power-down mode reduces the standby
power consumption to only 7 mW typical. The part is available
in a 24-lead, 0.3 inch-wide, plastic and hermetic dual-in-line
package (DIP) as well as a 24-lead small outline (SOIC) package.
PRODUCT HIGHLIGHTS
1. The programmable gain front end allows the AD7710 to
accept input signals directly from a strain gage or transducer,
removing a considerable amount of signal conditioning.
2. The AD7710 is ideal for microcontroller or DSP processor
applications with an on-chip control register that allows
control over filter cutoff, input gain, channel selection, signal
polarity, and calibration modes.
3. The AD7710 allows the user to read and write the on-chip
calibration registers. This means that the microcontroller has
much greater control over the calibration procedure.
4. No missing codes ensures true, usable, 23-bit dynamic range
coupled with excellent ±0.0015% accuracy. The effects of
temperature drift are eliminated by on-chip self-calibration,
which removes zero-scale and full-scale errors.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700 www.analog.com
Fax: 781/326-8703 © 2004 Analog Devices, Inc. All rights reserved.
CLOCK
GENERATION
SERIAL INTERFACE
CONTROL
REGISTER
OUTPUT
REGISTER
CHARGE-BALANCING A/D
CONVERTER
DIGITAL
FILTER
AD7710
M
U
X
PGA
AGND DGND MODE SDATA SCLK A0
MCLK
OUT
MCLK
IN
AIN1(+)
AIN1(–)
REF
IN (–)
REF
IN (+)
SYNC
4.5A
A = 1 – 128
DRDY
TFSRFS
REF OUT
2.5V REFERENCE
AV
DD
AV
DD
20A
AIN2(+)
AIN2(–)
I
OUT
V
SS
V
BIAS
AV
DD
DV
DD
AUTO-ZEROED
⌺-⌬
MODULATOR
