a
FEATURES
Charge-Balancing ADC
16 Bits No Missing Codes
0.0015% Nonlinearity
Programmable Gain Front End
Gains of 1, 2, 32 and 128
Differential Input Capability
Three-Wire Serial Interface
SPI™, QSPI™, MICROWIRE™ and DSP Compatible
Ability to Buffer the Analog Input
3 V (AD7715-3) or 5 V (AD7715-5) Operation
Low Supply Current: 450 A max @ 3 V Supplies
Low-Pass Filter with Programmable Output Update
16-Lead SOIC/DIP/TSSOP
AIN(+)
AIN(–)
3 V/5 V, 450 A
16-Bit, Sigma-Delta ADC
AD7715*
FUNCTIONAL BLOCK DIAGRAM
REF IN(–) REF IN(+)
AV
DD
DV
DD
CHARGE BALANCING
A/D CONVERTER
SIGMA-DELTA
MODULATOR
DIGITAL
FILTER
BUFFER
PGA
A = 1–128
CLOCK
GENERATION
MCLK IN
MCLK OUT
RESET
SCLK
CS
DIN
DOUT
DRDY
SERIAL
INTERFACE
REGISTER BANK
AD7715
AGND
DGND
GENERAL DESCRIPTION
The AD7715 is a complete analog front end for low frequency
measurement applications. The part can accept low level input
signals directly from a transducer and outputs a serial digital
word. It employs a sigma-delta conversion technique to realize
up to 16 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 pro-
cessed by an on-chip digital filter. The first notch of this digital
filter can be programmed via the on-chip control register allow-
ing adjustment of the filter cutoff and output update rate.
The AD7715 features a differential analog input as well as a dif-
ferential reference input. It operates from a single supply (+3 V
or +5 V). It can handle unipolar input signal ranges of 0 mV to
+20 mV, 0 mV to +80 mV, 0 V to +1.25 V and 0 V to +2.5 V.
It can also handle bipolar input signal ranges of
±
20 mV,
±
80 mV,
±
1.25 V and
±
2.5 V. These bipolar ranges are referenced to
the negative input of the differential analog input. The AD7715
thus performs all signal conditioning and conversion for a single-
channel system.
The AD7715 is ideal for use in smart, microcontroller or DSP
based systems. It features a serial interface that can be config-
ured for three-wire operation. Gain settings, signal polarity and
update rate selection can be configured in software using the
input serial port. The part contains self-calibration and system
calibration options to eliminate gain and offset errors on the
part itself or in the system.
SPI and QSPI are trademarks of Motorola, Inc.
MICROWIRE is a trademark of National Semiconductor Corporation.
*Protected
by U.S. Patent No: 5,134,401.
See page 30 for data sheet index.
CMOS construction ensures very low power dissipation, and the
power-down mode reduces the standby power consumption to
50
µW
typ. The part is available in a 16-lead, 0.3 inch-wide,
plastic dual-in-line package (DIP) as well as a 16-lead 0.3 inch-
wide small outline (SOIC) package and a 16-lead TSSOP package.
PRODUCT HIGHLIGHTS
1. The AD7715 consumes less than 450
µA
in total supply
current at 3 V supplies and 1 MHz master clock, making it
ideal for use in low-power systems. Standby current is less
than 10
µA.
2. The programmable gain input allows the AD7715 to accept
input signals directly from a strain gage or transducer remov-
ing a considerable amount of signal conditioning.
3. The AD7715 is ideal for microcontroller or DSP processor
applications with a three-wire serial interface reducing the
number of interconnect lines and reducing the number of
opto-couplers required in isolated systems. The part con-
tains on-chip registers which allow software control over
output update rate, input gain, signal polarity and calibration
modes.
4. The part features excellent static performance specifications
with 16-bits no missing codes,
±
0.0015% accuracy and low
rms noise (<550 nV). Endpoint errors and the effects of
temperature drift are eliminated by on-chip calibration op-
tions, which remove 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
World Wide Web Site: http://www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 2000
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