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LT1785/LT1785A

LT1791/LT1791A

60V Fault Protected

RS485/RS422 Transceivers

Normal Operation Waveforms at 250kBaud

GND1

GND2

1785/91 TA01

RO1

RE1

DE1

DI1

LT1785

RO2

RE2

DE2

DI2

LT1785

TX

TX

RX

RX

DESCRIPTIO

The LT

ferential bus transceivers for RS485 and RS422 applica-

tions which feature on-chip protection from overvoltage

faults on the data transmission lines. Receiver input and

driver output pins can withstand voltage faults up to

±60V

with respect to ground with no damage to the device.

Faults may occur while the transceiver is active, shut down

or powered off.

Data rates to 250kbaud on networks of up to 128 nodes are

supported. Controlled slew rates on the driver outputs

control EMI emissions and improve data transmission

integrity on improperly terminated lines. Drivers are speci-

fied to operate with inexpensive cables as low as 72

Ω

characteristic impedance.

The LT1785A/LT1791A devices have “fail-safe” receiver

inputs to guarantee a receiver output high for shorted,

open or inactive data lines. On-chip ESD protection elimi-

nates need for external protection devices.

The LT1785/LT1785A are available in 8-lead DIP and SO

packages and the LT1791/LT1791A in 14-lead DIP and SO

packages.

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Protected from Overvoltage Line Faults to

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Pin Compatible with LTC485 and LTC491

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High Input Impedance Supports Up to 128 Nodes

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No Damage or Latchup to ESD

IEC-1000-4-2 Level 4:

±15kV Air Discharge

IEC-1000-4-2 Level 2:

±4kV Contact Discharge

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Controlled Slew Rates for EMI Emissions Control

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Guaranteed High Receiver Output State for Floating,

Shorted or Inactive Inputs

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Outputs Assume a High Impedance When Off or

Powered Down

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Drives Low Cost, Low Impedance Cables

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Short-Circuit Protection on All Outputs

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Thermal Shutdown Protection

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Industrial Control Data Networks

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CAN Bus Applications

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HVAC Controls

1785/91 TA02

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

FEATURES

APPLICATIO S

TYPICAL APPLICATIO

RO

Y-Z

DI