LMS485

5V Low Power RS-485 / RS-422 Differential Bus

Transceiver

General Description

The LMS485 is a low power differential bus/line transceiver

designed for high speed bidirectional data communication on

multipoint bus transmission lines. It is designed for balanced

transmission lines. It meets ANSI Standards TIA/EIA

RS422-B, TIA/EIA RS485-A and ITU recommendation and

ferential line driver and differential input receiver, both of

which operate from a single 5.0V power supply. The driver

and receiver have an active high and active low, respec-

tively, that can be externally connected to function as a

direction control. The driver and receiver differential inputs

are internally connected to form differential input/output (I/O)

bus ports that are designed to offer minimum loading to bus

whenever the driver is disabled or when V

ports feature wide positive and negative common mode

voltage ranges, making the device suitable for multipoint

applications in noisy environments. The LMS485 is available

in a 8-Pin SOIC and 8-Pin DIP packages. It is a drop-in

socket replacement to Maxim’s MAX485

Features

n

Meet ANSI standard RS-485-A and RS-422-B

n

Data rate 2.5 Mbps

n

Single supply voltage operation, 5V

n

Thermal shutdown protection

n

Short circuit protection

n

Low power BiCMOS

n

Allows up to 32 transceivers on the bus

n

Open circuit fail-safe for receiver

n

Extended operating temperature range −40˚C to 85˚C

n

Drop-in replacement to MAX485

n

Available in 8-pin SOIC and 8-Pin DIP package

Applications

n

Low power RS-485 systems

n

Network hubs, bridges, and routers

n

Point of sales equipment (ATM, barcode scanners,…)

n

Local area networks (LAN)

n

Integrated service digital network (ISDN)

n

Industrial programmable logic controllers

n

High speed parallel and serial applications

n

Multipoint applications with noisy environment

Typical Application

20062601

A Typical multipoint application is shown in the above figure. Terminating resistors, RT, are typically required but only located at the two ends of the cable.

Pull up and pull down resistors maybe required at the end of the bus to provide failsafe biasing. The biasing resistors provide a bias to the cable when all

drivers are in TRI-STATE, See National Application Note, AN-847 for further information.

April 2003

© 2003 National Semiconductor Corporation

DS200626

www.national.com