REV. A

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a

AD7864

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., 1999

4-Channel, Simultaneous

Sampling, High Speed, 12-Bit ADC

FUNCTIONAL BLOCK DIAGRAM

STBY

FRSTDATA

INT/EXT CLOCK

SELECT

OUTPUT

DATA

REGISTERS

2.5V

REFERENCE

SIGNAL

SCALING

BUSY

SIGNAL

SCALING

SIGNAL

SCALING

SIGNAL

SCALING

TRACK/HOLD

4

EOC

WR

CS

DB0

DB11

RD

AGND

DGND

6k

AD7864

12-BIT

ADC

SOFTWARE

LATCH

CONVERSION

CONTROL LOGIC

MUX

CONVST SL1 SL2 SL3 SL4 H/S

SEL

CLKIN

INT/EXT

CLK

AGND AGND

INT

CLOCK

DB0–DB3

FEATURES

High Speed (1.65

s) 12-Bit ADC

Four Simultaneously Sampled Inputs

Four Track/Hold Amplifiers

0.35

s Track/Hold Acquisition Time

1.65

s Conversion Time per Channel

HW/SW Select of Channel Sequence for Conversion

Single Supply Operation

Selection of Input Ranges:

10 V,

5 V for AD7864-1

2.5 V for AD7864-3

0 V to 2.5 V, 0 V to 5 V for AD7864-2

High Speed Parallel Interface Which Also Allows

Interfacing to 3 V Processors

Low Power, 90 mW Typ

Power Saving Mode, 20

W Typ

Overvoltage Protection on Analog Inputs

APPLICATIONS

AC Motor Control

Uninterrupted Power Supplies

Data Acquisition Systems

Communications

GENERAL DESCRIPTION

The AD7864 is a high speed, low power, 4-channel simulta-

neous sampling 12-bit A/D converter that operates from a single

+5 V supply. The part contains a 1.65

µs successive approxima-

tion ADC, four track/hold amplifiers, 2.5 V reference, on-chip

clock oscillator, signal conditioning circuitry and a high speed

parallel interface. The input signals on four channels are

sampled simultaneously, thus preserving the relative phase infor-

mation of the signals on the four analog inputs. The part accepts

analog input ranges of

±10 V, ±5 V (AD7864-1), 0 V to 2.5 V,

0 V to 5 V for AD7864-2 and

±2.5 V (AD7864-3).

The part allows any subset of the four channels to be converted

in order to maximize the throughput rate on the selected se-

quence. The channels to be converted can be selected via either

hardware (channel select input pins) or software (programming

the channel select register).

A single conversion start signal (

CONVST) simultaneously

places all the track/holds into hold and initiates conversion se-

quence for the selected channels. The

EOC signal indicates the end

of each individual conversion in the selected conversion sequence.

The BUSY signal indicates the end of the conversion sequence.

Data is read from the part by means of a 12-bit parallel data

bus using the standard

CS and RD signals. Maximum through-

put for a single channel is 500 kSPS. For all four channels the

maximum throughput is 130 kSPS for the read during conver-

sion sequence operation. The throughput rate for the read after

conversion sequence operation will depend on the read cycle

time of the processor. See Timing and Control section.

The AD7864 is available in a small (0.3 sq. inch area) 44-lead

MQFP.

PRODUCT HIGHLIGHTS

1. The AD7864 features four Track/Hold amplifiers and a fast

(1.65

µs) ADC allowing simultaneous sampling and then

conversion of any subset of the four channels.

2. The AD7864 operates from a single +5 V supply and consumes

only 90 mW typ making it ideal for low power and portable

applications. Also see Standby Mode Operation.

3. The part offers a high speed parallel interface for easy con-

nection to microprocessors, microcontrollers and digital

signal processors.

4. The part is offered in three versions with different analog

input ranges. The AD7864-1 offers the standard industrial

input ranges of

±10 V and ±5 V; the AD7864-3 offers the

common signal processing input range of

±2.5 V; the

AD7864-2 can be used in unipolar 0 V to 2.5 V, 0 V to 5 V

applications.

5. The part features very tight aperture delay matching between

the four input sample-and-hold amplifiers.