a
AD7861
FUNCTIONAL BLOCK DIAGRAM
REF IN
BUSY
REF OUT
VIN1
VIN2
VIN3
A0
A1
D0
D11
RD
CS
CLKIN
SHA
2.5V
REFERENCE
AUX0
AUX1
AUX2
AUX3
S0
S1
CONVST
RESET
M0 M1
12
11-BIT
ADC
4-1
MUX
OUTPUT
REGISTERS
SGND
AGND
DGND
V
DD
AD7861
11-Bit Resolution
Simultaneous Sampling A/D Converter
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.
FEATURES
11-Bit Resolution Analog-to-Digital Converter
Seven Single-Ended Analog Inputs
Four Input Channels Simultaneously Sampled
Expansion with 4 Multiplexed Inputs
Internal 2.5 V Reference
3.2 s Conversion Time per Channel
User Definable Channel Sequencing
Single Supply +5 V Operation
Double Buffered Register Outputs
6.25 MHz to 12.5 MHz Operating Clock Range
APPLICATIONS
Motor Control
3-Phase Power Measurement
Cellular Phones
Data Acquisition
GENERAL DESCRIPTION
The AD7861 is a multichannel simultaneous sampling A/D
Converter (ADC) configured for the acquisition of voltage
inputs in a motor control solution or three-phase power system.
The AD7861 combined with Analog Devices’ 16-bit fixed-
point digital signal processor (DSP) provides a low cost 16-bit
fixed-point microcontroller solution.
The input stage has been designed to accommodate the types of
signals frequently found in motor drives. The VIN1, VIN2, and
VIN3 channels are simultaneously sampled inputs suitable for
stator current acquisition. The AUX0–AUX3 channels are
multiplexed and are suitable for slower moving inputs such as
temperature and bus voltage of the diode rectifier output in a
motor control application.
PRODUCT HIGHLIGHTS
Simultaneous Sampling of Four Inputs
Four channel sample and hold amplifier (SHA) allows out of
phase input signals to be sampled simultaneously, preserving
the relative phase information. Sample-and-hold acquisition
time is 1.6 µs and conversion time per channel is 3.2 µs (using
a 12.5 MHz system clock).
Flexible Analog Channel Sequencing
AD7861 supports acquisition of 2, 3 or 4 channels per group.
Converted channel results are stored in registers and the data
can be read in any order. The sampling and conversion time
for two channels is 8 µs, three channels is 11.2 µs, and four
channels is 14.4 µs (using a 12.5 MHz system clock).
Single 5 V dc Operation
Low power, digital process.
REV. B
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
