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

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