a
FEATURES
Charge Balancing ADC
24 Bits No Missing Codes
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)
Low Current (350 A typ) with Power-Down (5 A typ)
AD7714Y Grade:
+2.7 V to 3.3 V or +4.75 V to +5.25 V Operation
0.0010% Linearity Error
–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
APPLICATIONS
Portable Industrial Instruments
Portable Weigh Scales
Loop-Powered Systems
Pressure Transducers
GENERAL DESCRIPTION†
AIN1
AIN2
AIN3
AIN4
AIN5
AIN6
3 V/5 V, CMOS, 500 A
Signal Conditioning ADC
AD7714*
FUNCTIONAL BLOCK DIAGRAM
AV
DD
DV
DD
REF IN(–) REF IN(+)
AV
DD
1 A
SWITCHING
MATRIX
CHARGE
BALANCING
A/D CONVERTER
Σ
-∆
MODULATOR
BUFFER
PGA
A = 1–128
1 A
SERIAL INTERFACE
REGISTER BANK
DIGITAL FILTER
STANDBY
SYNC
AGND
BUFFER
MCLK IN
MCLK OUT
CLOCK
GENERATION
SCLK
CS
DIN
DOUT
AD7714
AGND
DGND
POL
DRDY
RESET
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.
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).
PRODUCT HIGHLIGHTS
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.
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
*Protected
by U.S. Patent No. 5,134,401.
†See page 39 for data sheet index.
SPI and QSPI are trademarks of Motorola, Inc.
MICROWIRE is a trademark of National Semiconductor Corporation.
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.
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
(f
CLK IN
= 1 MHz)
or 1 mA (f
CLK 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.
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.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
World Wide Web Site: http://www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 1998
AD [ ANALOG DEVICES ]
