REV. A
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a
AD7856
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
5 V Single Supply, 8-Channel
14-Bit 285 kSPS Sampling ADC
FUNCTIONAL BLOCK DIAGRAM
4.096V
REFERENCE
AV
DD
AGND
DV
DD
DGND
CLKIN
CONVST
BUSY
SLEEP
CAL
C
REF2
C
REF1
REF
IN
/REF
OUT
AIN8
AIN1
DIN DOUT SCLK
SYNC
SERIAL INTERFACE/CONTROL REGISTER
BUF
CHARGE
REDISTRIBUTION
DAC
AD7856
.....
....
COMP
CALIBRATION
MEMORY AND
CONTROLLER
SAR + ADC
CONTROL
T/H
I/P
MUX
PRODUCT HIGHLIGHTS
1. Single 5 V supply.
2. Automatic calibration on power-up.
3. Flexible power management options including automatic
power-down after conversion.
4. Operates with reference voltages from 1.2 V to V
DD
.
5. Analog input range from 0 V to V
DD
.
6. Eight single-ended or four pseudo-differential input channels.
7. Self- and system calibration.
8. Versatile serial I/O port (SPI/QSPI/8051/µP).
GENERAL DESCRIPTION
The AD7856 is a high speed, low power, 14-bit ADC that oper-
ates from a single 5 V power supply. The ADC powers up with
a set of default conditions at which time it can be operated as a
read only ADC. The ADC contains self-calibration and system
calibration options to ensure accurate operation over time and
temperature and it has a number of power-down options for low
power applications.
The AD7856 is capable of 285 kHz throughput rate. The input
track-and-hold acquires a signal in 500 ns and features a pseudo-
differential sampling scheme. The AD7856 voltage range is 0 to
V
REF
with straight binary output coding. Input signal range is to
the supply and the part is capable of converting full power sig-
nals to 10 MHz.
CMOS construction ensures low power dissipation of typically
60 mW for normal operation and 5.1 mW in power-down mode
at 10 kSPS throughput rate. The part is available in 24-lead,
0.3 inch-wide dual in-line package (DIP), 24-lead small outline
(SOIC) and 24-lead small shrink outline (SSOP) packages.
Please see page 31 for data sheet index.
FEATURES
Single 5␣ V Supply
285 kSPS Throughput Rate
Self- and System Calibration with Autocalibration on
Power-Up
Eight Single-Ended or Four Pseudo-Differential Inputs
Low Power: 60 mW Typ
Automatic Power-Down After Conversion (2.5␣ W Typ)
Flexible Serial Interface: 8051/SPI™/QSPI™/P Compatible
24-Lead DIP, SOIC and SSOP Packages
APPLICATIONS
Battery-Powered Systems (Personal Digital Assistants,
Medical Instruments, Mobile Communications)
Pen Computers
Instrumentation and Control Systems
High Speed Modems
SPI and QSPI are trademarks of Motorola, Inc.
