GENERAL DESCRIPTION

The ADM2481 differential bus transceiver is an integrated, galvanically isolated component designed for bidirectional data communication on balanced, multipoint bus transmission lines. It complies with ANSI EIA/TIA-485-A and ISO 8482: 1987(E). Using iCoupler? technology from Analog Devices, Inc., the ADM2481 combines a 3-channel isolator, a three-state diffe-rential line driver, and a differential input receiver into a single package. The logic side of the device is powered with either a 5 V or 3 V supply, and the bus side uses a 5 V supply only.

The ADM2481 is slew-limited to reduce reflections with improp-erly terminated transmission lines. The controlled slew rate limits the data rate to 500 kbps. The input impedance of the device is 96 kΩ, allowing up to 256 transceivers on the bus. Its driver has an active-high enable feature. The driver differential outputs and receiver differential inputs are connected internally

to form a differential input/output (I/O) port. When the driver is disabled or when VDD1 or VDD2 = 0 V, this imposes minimal loading on the bus. An active-high receiver disable feature, which causes the receiver output to enter a high impedance state, is provided as well.

The receiver inputs have a true fail-safe feature that ensures a logic-high receiver output level when the inputs are open or shorted. This guarantees that the receiver outputs are in a known state before communication begins and at the point when communication ends.

Current limiting and thermal shutdown features protect against output short circuits and bus contention situations that might cause excessive power dissipation. The part is fully specified over the industrial temperature range of ?40°C to +85°C and is available in a 16-lead, wide body SOIC package.

FEATURES

RS-485 transceiver with electrical data isolation

Complies with ANSI TIA/EIA-485-A and ISO 8482: 1987(E)

500 kbps data rate

Slew rate-limited driver outputs

Low power operation: 2.5 mA maximum

Suitable for 5 V or 3.3 V operations (VDD1)

High common-mode transient immunity: >25 kV/μs

True fail-safe receiver inputs

Chatter-free power-up/power-down protection

256 nodes on bus

Thermal shutdown protection

Safety and regulatory approvals

UL recognition: 2500 V rms for 1 minute per UL 1577

VDE certificates of conformity

DIN V VDE V 0884-10 (VDE V 0884-10): 2006-12

VIORM = 560 V peak

Operating temperature range: ?40°C to +85°C

APPLICATIONS

Low power RS-485/RS-422 networks

Isolated interfaces

Building control networks

Multipoint data transmission systems