Half-Duplex, iCoupler

Isolated RS-485 Transceiver

ADM2481

Rev. 0

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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

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 (pending)

UL recognition: 2500 V rms for 1 minute per

UL 1577 (pending)

VDE certificates of conformity (pending)

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

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

FUNCTIONAL BLOCK DIAGRAM

ADM2481

DE

TxD

RxD

A

B

RE

Figure 1.

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 I/O port. When the driver is disabled or

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.