LMS485 Datasheet, PDF (1/13 Pages) National Semiconductor (TI) – 5V Low Power RS-485 / RS-422 Differential Bus

April 2003
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
V.11 and X.27. The LMS485 combines a TRI-STATE™ dif-
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_CC = 0V. These
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.
© 2003 National Semiconductor Corporation DS200626
www.national.com