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High Speed Isolated RS-485 Transceiver

with Integrated Transformer Driver

Preliminary Technical Data

ADM2485

FEATURES

Half-duplex isolated RS-485 transceiver

Integrated oscillator driver for external transformer

PROFIBUS compliant

Complies with ANSI TIA/EIA RS-485-A-1998 and

ISO 8482:1987(E)

16 Mbps data rate

50 nodes on bus

Receiver open-circuit, fail-safe design

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

Isolated DE OUT status output

Thermal shutdown protection

Safety and regulatory approvals (pending):

CSA component acceptance notice #5A

VDE certificate of conformity

DIN EN 60747-5-2 (VDE 0884 Part 2): 2003-01

DIN EN 60950 (VDE 0805):2001-12; EN 60950: 2000

Operating temperature range: -40° to 85°C

Wide body 16-lead SOIC package

APPLICATIONS

Isolated RS-485/RS-422 interfaces

PROFIBUS networks

Industrial field networks

Multipoint data transmission systems

GENERAL DESCRIPTION

The ADM2485 differential bus transceiver is an integrated,

galvanically isolated component designed for bidirectional data

communication on multipoint bus transmission lines. It is

designed for balanced transmission lines and complies with

ANSI TIA/EIA RS-485-A-1998 and ISO 8482:1987(E).

The device employs Analog Devices’ iCoupler technology to

combine a 3-channel isolator, a 3-state differential line driver,

and a differential input receiver into a single package. An on-

chip oscillator outputs a pair of square waveforms which drive

an external transformer to provide isolated power with an

external transformer. The logic side of the device can be

powered with either a 5 V or a 3 V supply while the bus side is

powered with an isolated 5 V supply.

The ADM2485 driver has an active high enable. The driver

differential outputs and the receiver differential inputs are

connected internally to form a differential input/output port

that imposes minimal loading on the bus when the driver is

high receiver disable that causes the receive output to enter a

high impedance state.

The device has current-limiting and thermal shutdown features

to protect against output short circuits and situations where bus

contention might cause excessive power dissipation. The part is

fully specified over the industrial temperature range and is

available in a 16-lead wide-body SOIC package.

FUNCTIONAL BLOCK DIAGRAM

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Figure 1

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