LMS1485

5V Low Power RS-485 Differential Bus Transceiver

General Description

The LMS1485 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

V.11 and X.27.

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, respectively, that can be

externally connected to function as a direction control. The

driver and receiver differential inputs are internally con-

nected 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

wide positive and negative common mode voltage ranges,

making the device suitable for multipoint applications in

noisy environments.

The LMS1485 is build with National’s advanced BiCMOS

process and is available in a 8-Pin SOIC package. It is a

drop-in socket replacement to ADI’s ADM1485 and LTC’s

LT1485.

Features

n

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

n

Data rate 30Mbps

n

Single supply voltage operation, 5V

n

Wide input and output voltage range

n

Thermal shutdown protection

n

Short circuit protection

n

Driver propagation delay 10ns

n

Receiver propagation delay 25ns

n

High impedance outputs with power off

n

Open circuit fail-safe for receiver

n

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

n

ESD rating 8kV HBM

n

Drop-in replacement to ADM1485 and LT1485

n

Available in 8-pin SOIC

n

Low supply current, I

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

20048801

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.

July 2003

© 2003 National Semiconductor Corporation

DS200488

www.national.com