LT1785/LT1785A/
LT1791/LT1791A
60V Fault Protected
RS485/RS422 Transceivers
Features
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Description
Protected from Overvoltage Line Faults to ±60V
Pin Compatible with LTC485 and LTC491
High Input Impedance Supports Up to 128 Nodes
No Damage or Latchup to ESD
n IEC-1000-4-2 Level 4: ±15kV Air Discharge
n IEC-1000-4-2 Level 2: ±4kV Contact Discharge
Controlled Slew Rates for EMI Emissions Control
Guaranteed High Receiver Output State for Floating,
Shorted or Inactive Inputs (LT1785A/LT1791A)
Outputs Assume a High Impedance When Off or
Powered Down
Drives Low Cost, Low Impedance Cables
Short-Circuit Protection on All Outputs
Thermal Shutdown Protection
Guaranteed Operation to 125°C
Applications
Industrial Control Data Networks
CAN Bus Applications
n HVAC Controls
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L, LT, LTC, LTM, µModule, Linear Technology and the Linear logo are registered trademarks of
Linear Technology Corporation. All other trademarks are the property of their respective owners.
The LT®1785/LT1791 are half-duplex and full-duplex differential bus transceivers for RS485 and RS422 applications
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 outputscontrol EMI emissions and improve data transmission integrity on improperly terminated lines. Drivers are
specified to operate with inexpensive cables as low as
72Ω 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 eliminates
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.
Typical Application
Normal Operation Waveforms at 250kBaud
RO1
RE1
DE1
DI1
RX
LT1785
VCC1
RO
RTERM
TX
Y-Z
GND1
RO2
RE2
DE2
DI2
RX
LT1785
TX
DI
VCC2
RTERM
178591 TA02
GND2
178591 TA01
178591fd
For more information www.linear.com/LT1785
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