1

LTC1535

Isolated RS485 Transceiver

August 1999

, LTC and LT are registered trademarks of Linear Technology Corporation.

Final Electrical Specifications

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.

However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-

tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

The LTC

line transceiver. Isolated RS485 is ideal for systems where

the ground loop is broken to allow for much larger com-

mon mode voltage ranges. An internal capacitive isolation

transceiver and the logic level interface. The powered side

contains a 400kHz push-pull converter to power the iso-

lated RS485 transceiver. Internal full-duplex communica-

tion occurs through the capacitive isolation barrier. The

transceiver meets RS485 and RS422 requirements.

The driver and receiver feature three-state outputs, with

the driver maintaining high impedance over the entire

common mode range. The drivers have short-circuit cur-

rent limits in both directions and a slow slew rate select to

minimize EMI or reflections. The 68k

Ω receiver input

allows up to 128 node connections. A fail-safe feature

defaults to a high output state when the receiver inputs are

open or shorted.

s

Isolated RS485 Receiver/Driver

s

RS485 with Large Common Mode Voltage

s

Breaking RS485 Ground Loops

s

Multiple Unterminated Line Taps

s

s

Half- or Full-Duplex

s

Eliminates Ground Loops

s

350kBd Maximum Data Rate

s

Self-Powered with 400kHz Converter

s

Fail-Safe Output High for Open or

Shorted Receiver Inputs

s

Short-Circuit Current Limit

s

Slow Slew Rate Control

s

68k

Ω Input Impedance Allows Up to 128 Nodes

s

Thermal Shutdown

s

8kV ESD Protection On Driver Outputs and Receiver

Inputs

TYPICAL APPLICATIO

APPLICATIO S

FEATURES

DESCRIPTIO

**

D

Y

Z

SLO

2

1

1

R

A

B

RO2

1535 TA01

RO

RE

DE

DI

GND

LOGIC COMMON

2

FLOATING RS485 COMMON

** TRANSFORMER

COILTRONICS (561) 241-7876

400kHz

28

27

26

25

4

17

15

16

18

12

13

14

11

1

+

+

GND2

1/2 BAT54C

1/2 BAT54C

ST1

ST2

3

2

RO

RE

DE

DI

1

10

µF

10

µF

2

CTX02-14659

TWISTED-PAIR

CABLE