GENERAL DESCRIPTION

The ADM1485 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 both RS-485 and RS-422 EIA Standards. The part contains a differential line driver and a differential line receiver. Both the driver and the receiver may be enabled independently. When disabled, the outputs are three-stated.

The ADM1485 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. This feature forces the driver output into a high impedance state if, during fault condi tions, a significant temperature increase is detected in the internal driver circuitry.

Up to 32 transceivers may 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 ADM1485 driver features high output impedance when disabled and also when powered down.

This minimizes the loading effect when the transceiver is not being used. The high impedance driver output is maintained over the entire common-mode voltage range from –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 ADM1485 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 ADM1485 features extremely fast switching speeds. Minimal driver propagation delays permit transmission at typical data rates of 30 Mbps while low skew minimizes EMI interference.

The part is fully specified over the commercial and industrial temperature range and is available in PDIP, SOIC, and small MSOP packages.

FEATURES

Meets EIA RS-485 Standard

30 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

Receiver Propagation Delay: 15 ns

High-Z Outputs with Power Off

Superior Upgrade for LTC1485

APPLICATIONS

Low Power RS-485 Systems

DTE-DCE Interface

Packet Switching

Local Area Networks

Data Concentration

Data Multiplexers

Integrated Services Digital Network (ISDN)