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a

1-, 4- & 8-Channel 10-Bit ADCs

AD7776/AD7777/AD7778*

FUNCTIONAL BLOCK DIAGRAMS

CS

RD WR BUSY/INT

AGND

DB0–DB9

AD7776

10

DGND

CLKIN

10

CONTROL

REGISTER

ADCREG1

T/H

REFOUT

REFIN

REF

AGND

RTN

MUX

REFIN

10-BIT

ADC

CONTROL LOGIC

AGND

DB0–DB9

AD7777

10

CONTROL

REGISTER

DGND

CLKIN

10

ADCREG2

ADCREG1

T/H

1

REFOUT

REFIN

REF

AGND

MUX

1

REFIN

T/H

2

MUX

2

10-BIT

ADC

CONTROL LOGIC

RTN

AGND

DB0–DB9

AD7778

10

CONTROL

REGISTER

DGND

CLKIN

CS

RD WR BUSY/INT

10

ADCREG2

ADCREG1

T/H

1

REFOUT

REFIN

REF

AGND

MUX

1

REFIN

T/H

2

MUX

2

10-BIT

ADC

CONTROL LOGIC

RTN

FEATURES

AD7776: Single Channel

AD7777: 4-Channel

AD7778: 8-Channel

Fast 10-Bit ADC: 2.5

s Worst Case

+5 V Only

Half-Scale Conversion Option

Fast Interface Port

Power-Down Mode

APPLICATIONS

HDD Servos

Instrumentation

GENERAL DESCRIPTION

The AD7776, AD7777 and AD7778 are a family of high speed,

multichannel, 10-bit ADCs primarily intended for use in R/W

head positioning servos found in high density hard disk drives.

They have unique input signal conditioning features that make

them ideal for use in such single supply applications.

By setting a bit in a control register within both the four-channel

version, AD7777, and the eight-channel version, AD7778, the

input channels can either be independently sampled or any two

channels of choice can be simultaneously sampled. For all ver-

±

analog input signal range becomes 0 V to +2 V for all input

channels. This is covered in more detail under the section

is the offset of the ADC’s midpoint code from ground and is

supplied either by an onboard reference available to the user

(REFOUT) or by an external voltage reference applied to

REFIN. The full-scale range (FSR) of the ADC is equal to

tionally, when placed in the half-scale conversion mode, the

value of REFIN is converted. This allows the channel offset(s)

to be measured.

Control register loading and ADC register reading, channel se-

lect and conversion start are under the control of the

µP. The

twos complemented coded ADCs are easily interfaced to a stan-

dard 16-bit MPU bus via their 10-bit data port and standard

microprocessor control lines.

The AD7776/AD7777/AD7778 are fabricated in linear compat-

ible CMOS (LC

that combines precision bipolar circuits with low power CMOS

logic. The AD7776 is available in a 24-pin SOIC package; the

AD7777 is available in both 28-pin DIP and 28-pin SOIC pack-

ages; the AD7778 is available in a 44-pin PQFP package.

*Protected by U.S. Patent No. 4,990,916.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.

Tel: 617/329-4700

World Wide Web Site: http://www.analog.com

Fax: 617/326-8703

© Analog Devices, Inc., 1997