5 V Low Power

EIA RS-485 Transceiver

ADM485

Rev. F

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FEATURES

Meets EIA RS-485 standard

5 Mbps data rate

Single 5 V supply

–7 V to +12 V bus common-mode range

High speed, low power BiCMOS

Thermal shutdown protection

Short-circuit protection

Driver propagation delay: 10 ns typical

Receiver propagation delay: 15 ns typical

High-Z outputs with power off

Superior upgrade for LTC485

APPLICATIONS

Low power RS-485 systems

DTE/DCE interface

Packet switching

Local area networks (LNAs)

Data concentration

Data multiplexers

Integrated services digital network (ISDN)

FUNCTIONAL BLOCK DIAGRAM

A

GND

B

VCC

R

D

RO

RE

DE

DI

ADM485

1

2

3

4

8

7

6

5

Figure 1.

GENERAL DESCRIPTION

The ADM485 is a differential line transceiver suitable for high

speed bidirectional data communication on multipoint bus

transmission lines. It is designed for balanced data transmission

and complies with EIA standards RS-485 and RS-422. The part

contains a differential line driver and a differential line receiver.

Both the driver and the receiver can be enabled independently.

When disabled, the outputs are three-stated.

The ADM485 operates from a single 5 V power supply.

Excessive power dissipation caused by bus contention or by

output shorting is prevented by a thermal shutdown circuit. If

during fault conditions, a significant temperature increase is

detected in the internal driver circuitry, this feature forces the

driver output into a high impedance state.

Up to 32 transceivers can be connected simultaneously on a

bus, but only one driver should be enabled at any time. It is

important, therefore, that the remaining disabled drivers do not

load the bus. To ensure this, the ADM485 driver features high

output impedance when disabled and when powered down,

which minimizes the loading effect when the transceiver is not

being used. The high impedance driver output is maintained

over the common-mode voltage range of −7 V to +12 V.

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

high output state if the inputs are unconnected (floating).

The ADM485 is fabricated on BiCMOS, an advanced mixed

technology process combining low power CMOS with fast

switching bipolar technology. All inputs and outputs contain

protection against ESD; all driver outputs feature high source

and sink current capability. An epitaxial layer is used to guard

against latch-up.

The ADM485 features extremely fast switching speeds. Minimal

driver propagation delays permit transmission at data rates up

to 5 Mbps while low skew minimizes EMI interference.

The part is fully specified over the commercial and industrial

temperature range and is available in 8-lead PDIP, 8-lead SOIC,

and small footprint, 8-lead MSOP packages.