REV. D
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AD7713
LC
2
MOS
Loop-Powered Signal Conditioning ADC
FEATURES
Charge Balancing ADC
24 Bits No Missing Codes
ⴞ0.0015% Nonlinearity
3-Channel Programmable Gain Front End
Gains from 1 to 128
2 Differential Inputs
1 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
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 available
in a 24-lead, 0.3 inch wide, PDIP and CERDIP as well as a 24-
lead SOIC package.
PRODUCT HIGHLIGHTS
1. The AD7713 consumes less than 1 mA in total supply current,
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 3-wire and 4-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
calibration modes. The AD7713 allows the user to read and
write the on-chip calibration registers.
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 ⌺-⌬ conversion
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 that can be used
to provide excitation in 3-wire and 4-wire RTD configurations.
The AD7713 thus performs all signal conditioning and conver-
sion 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.
FUNCTIONAL BLOCK DIAGRAM
CHARGING BALANCING ADC
AUTO-ZEROED
⌺-⌬
MODULATOR
DIGITAL
FILTER
CLOCK
GENERATION
AD7713
AGND DGND
MCLK
OUT
MCLK
IN
AIN1(+)
AIN1(–)
AIN2(+)
REF
IN(+)
AV
DD
DV
DD
AV
DD
1A
A = 1 – 128
STANDBY
AIN2(–)
REF
IN(–)
SYNC
RTD2
RTD1
PGA
AV
DD
200A
200A
MUX
SERIAL INTERFACE
CONTROL
REGISTER
OUTPUT
REGISTER
MODE SDATA A0DRDYTFSRFS SCLK
AIN3
INPUT
SCALING
