3 V/5 V, CMOS, 500 A
a
Signal Conditioning ADC
AD7714
FEATURES
Charge Balancing ADC
24 Bits No Missing Codes
FUNCTIONAL BLOCK DIAGRAM
DV
AV
REF IN(–)
REF IN(+)
DD
DD
0.0015% Nonlinearity
Five-Channel Programmable Gain Front End
Gains from 1 to 128
Can Be Configured as Three Fully Differential
Inputs or Five Pseudo-Differential Inputs
Three-Wire Serial Interface
SPI™, QSPI™, MICROWIRE™ and DSP Compatible
3 V (AD7714-3) or 5 V (AD7714-5) Operation
Low Noise (<150 nV rms)
AV
DD
CHARGE
BALANCING
A/D CONVERTER
1A
STANDBY
SYNC
Σ -∆
MODULATOR
AIN1
AIN2
AIN3
AIN4
AIN5
AIN6
BUFFER
PGA
DIGITAL FILTER
A = 1–128
1A
SERIAL INTERFACE
REGISTER BANK
SCLK
CS
AGND
BUFFER
Low Current (350 A typ) with Power-Down (5 A typ)
AD7714Y Grade:
MCLK IN
DIN
CLOCK
GENERATION
AD7714
DGND
MCLK OUT
+2.7 V to 3.3 V or +4.75 V to +5.25 V Operation
0.0010% Linearity Error
DOUT
–40؇C to +105؇C Temperature Range
Schmitt Trigger on SCLK and DIN
Low Current (226 A typ) with Power-Down (4 A typ)
Lower Power Dissipation than Standard AD7714
Available in 24-Lead TSSOP Package
Low-Pass Filter with Programmable Filter Cutoffs
Ability to Read/Write Calibration Coefficients
POL
RESET
DRDY
AGND
for three-wire operation. Gain settings, signal polarity and channel
selection can be configured in software using the serial port. The
AD7714 provides self-calibration, system calibration and back-
ground calibration options and also allows the user to read and
write the on-chip calibration registers.
APPLICATIONS
CMOS construction ensures very low power dissipation, and the
power-down mode reduces the standby power consumption to
15 µW typ. The part is available in a 24-pin, 0.3 inch-wide, plastic
dual-in-line package (DIP); a 24-lead small outline (SOIC)
package, a 28-lead shrink small outline package (SSOP) and a
24-lead thin shrink small outline package (TSSOP).
Portable Industrial Instruments
Portable Weigh Scales
Loop-Powered Systems
Pressure Transducers
GENERAL DESCRIPTION†
The AD7714 is a complete analog front end for low-frequency
measurement applications. The device accepts low level signals
directly from a 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 adjust-
ment of the filter cutoff and settling time.
PRODUCT HIGHLIGHTS
1. The AD7714Y offers the following features in addition to the
standard AD7714: wider temperature range, Schmitt trigger
on SCLK and DIN, operation down to 2.7 V, lower power
consumption, better linearity, and availability in 24-lead
TSSOP package.
2. The AD7714 consumes less than 500 µA (fCLK IN = 1 MHz)
or 1 mA (fCLK IN = 2.5 MHz) in total supply current, making
it ideal for use in loop-powered systems.
3. The programmable gain channels allow the AD7714 to ac-
cept input signals directly from a strain gage or transducer
removing a considerable amount of signal conditioning.
4. The AD7714 is ideal for microcontroller or DSP processor
applications with a three-wire serial interface reducing the num-
ber of interconnect lines and reducing the number of opto-
couplers required in isolated systems. The part contains
on-chip registers that allow control over filter cutoff, input gain,
channel selection, signal polarity and calibration modes.
The part features three differential analog inputs (which can also
be configured as five pseudo-differential analog inputs) as well as a
differential reference input. It operates from a single supply (+3 V
or +5 V). The AD7714 thus performs all signal conditioning and
conversion for a system consisting of up to five channels.
The AD7714 is ideal for use in smart, microcontroller- or DSP-
based systems. It features a serial interface that can be configured
†See page 39 for data sheet index.
SPI and QSPI are trademarks of Motorola, Inc.
MICROWIRE is a trademark of National Semiconductor Corporation.
5. The part features excellent static performance specifications
with 24-bit no missing codes, ±0.0015% accuracy and low
rms noise (140 nV). Endpoint errors and the effects of tem-
perature drift are eliminated by on-chip self-calibration,
which removes zero-scale and full-scale errors.
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.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
Fax: 781/326-8703
World Wide Web Site: http://www.analog.com
© Analog Devices, Inc., 1998
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