AD7713 Datasheet, PDF (1/28 Pages) Analog Devices – LC2MOS Loop-Powered Signal Conditioning ADC

a
LC²MOS
Loop-Powered Signal Conditioning ADC
AD7713*
FEATURES
Charge Balancing ADC
24 Bits No Missing Codes
؎0.0015% Nonlinearity
Three-Channel Programmable Gain Front End
Gains from 1 to 128
Two Differential Inputs
One Single Ended High Voltage Input
Low-Pass Filter with Programmable Filter Cutoffs
Ability to Read/Write Calibration Coefficients
Bidirectional Microcontroller Serial Interface
Single Supply Operation
Low Power (3.5 mW typ) with Power-Down Mode
(150 ␮W typ)
APPLICATIONS
Loop Powered (Smart) Transmitters
RTD Transducers
Process Control
Portable Industrial Instruments
GENERAL DESCRIPTION
The AD7713 is a complete analog front end for low frequency
measurement applications. The device accepts low level signals
directly from a transducer or high level signals (4 × V_REF) and
outputs a serial digital word. It employs a sigma-delta con-
version technique to realize up to 24 bits of no missing codes
performance. The input signal is applied to a proprietary pro-
grammable 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 one single-
ended high level analog input as well as a differential reference
input. It can be operated from a single supply (AV_DD and DV_DD
at +5 V). The part provides two current sources which can be
used to provide excitation in three-wire and four-wire RTD con-
figurations. The AD7713 thus performs all signal conditioning
and conversion for a single, dual or three-channel system.
The AD7713 is ideal for use in smart, microcontroller-based
systems. Gain settings, signal polarity and RTD current control
can be configured in software using the bidirectional serial port.
The AD7713 contains self-calibration, system calibration and
background calibration options and also allows the user to read
and to write the on-chip calibration registers.
*Protected by U.S. Patent No. 5,134,401.
AIN1(+)
AIN1(–)
AIN2(+)
AIN2(–)
AIN3
RTD1
RTD2
FUNCTIONAL BLOCK DIAGRAM
REF REF
AV_DD DV_{DD IN(–)} IN(+)
V_BIAS
STANDBY
AV_DD
AD7713
1µA
CHARGING BALANCING A/D
CONVERTER
INPUT
SCALING
M PGA
AUTO-ZEROED
∑−∆
MODULATOR
DIGITAL
FILTER
U
X
A = 1 – 128
CLOCK
GENERATION
200µA ^AVDD
200µA
SERIAL INTERFACE
CONTROL
REGISTER
OUTPUT
REGISTER
SYNC
MCLK
IN
MCLK
OUT
AGND DGND RFS TFS MODE SDATA SCLK DRDY A0
CMOS construction ensures low power dissipation and a hard-
ware programmable power-down mode reduces the standby
power consumption to only 150 µW typical. The part is avail-
able in a 24-pin, 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 AD7713 consumes less than 1 mA in total supply cur-
rent, making it ideal for use in loop-powered systems.
2. The two programmable gain channels allow the AD7713 to
accept input signals directly from a transducer removing a
considerable amount of signal conditioning. To maximize the
flexibility of the part, the high level analog input accepts
4 × V_REF signals. On-chip current sources provide excitation
for three-wire and four-wire RTD configurations.
3. No Missing Codes ensures true, usable, 24-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.
4. The AD7713 is ideal for microcontroller or DSP processor
applications with an on-chip control register which allows
control over filter cutoff, input gain, signal polarity and cali-
bration modes. The AD7713 allows the user to read and
write the on-chip calibration registers.
REV. C
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
© Analog Devices, Inc., 1995
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