REV. 0

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a

ADM3491

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

3.3 V, Full Duplex, 840 A

20 Mbps, EIA RS-485 Transceiver

FUNCTIONAL BLOCK DIAGRAM

R

D

RE

DE

DI

A

B

Z

Y

ADM3491

RO

FEATURES

Operates with +3.3 V Supply

EIA RS-422 and RS-485 Compliant Over Full CM Range

19 k

Input Impedance

Up to 50 Transceivers on Bus

20 Mbps Data Rate

Short Circuit Protection

Specified Over Full Temperature Range

Thermal Shutdown

Interoperable with 5 V Logic

840

A Supply Current

2 nA Shutdown Current

Also Available in TSSOP Package

Meets IEC1000-4-4 (>1 kV)

8 ns Skew

Upgrade for MAX 3491, SN75ALS180

APPLICATIONS

Telecommunications

DTE-DCE Interface

Packet Switching

Local Area Networks

Data Concentration

Data Multiplexers

Integrated Services Digital Network (ISDN)

AppleTalk

Industrial Controls

GENERAL DESCRIPTION

The ADM3491 is a low power differential line transceiver

designed to operate using a single +3.3 V power supply. Low

power consumption coupled with a shutdown mode make it

ideal for power sensitive applications. It is suitable for commu-

nication on multipoint bus transmission lines.

It is intended for balanced data transmission and complies with

both EIA Standards RS-485 and RS-422. It contains a differen-

tial line driver and a differential line receiver, making it suitable

for full duplex data transfer.

The input impedance is 19 k

Ω allowing up to 50 transceivers to

be connected on the bus.

Excessive power dissipation caused by bus contention or by

output shorting is prevented by a thermal shutdown circuit.

This feature forces the driver output into a high impedance state

if, during fault conditions, a significant temperature increase is

detected in the internal driver circuitry.

The receiver contains a fail-safe feature that results in a

logic high output state if the inputs are unconnected

(floating).

The ADM3491 is fabricated on BiCMOS, an advanced

mixed technology process combining low power CMOS

with fast switching bipolar technology.

The ADM3491 is fully specified over the industrial tem-

perature range and is available in DIP and SOIC packages

as well as a new space saving TSSOP package.