Datasheet

LT1785/LT1785A/
LT1791/LT1791A
1
178591fc
TYPICAL APPLICATION
DESCRIPTION
60V Fault Protected
RS485/RS422 Transceivers
The LT
®
1785/LT1791 are half-duplex and full-duplex differ-
ential 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 out-
putscontrol EMI emissions and improve data transmis-
sion integrity on improperly terminated lines. Drivers are
specifi ed 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.
Normal Operation Waveforms at 250kBaud
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
FEATURES
APPLICATIONS
n
Protected from Overvoltage Line Faults to ±60V
n
Pin Compatible with LTC485 and LTC491
n
High Input Impedance Supports Up to 128 Nodes
n
No Damage or Latchup to ESD
IEC-1000-4-2 Level 4: ±15kV Air Discharge
IEC-1000-4-2 Level 2: ±4kV Contact Discharge
n
Controlled Slew Rates for EMI Emissions Control
n
Guaranteed High Receiver Output State for Floating,
Shorted or Inactive Inputs
n
Outputs Assume a High Impedance When Off or
Powered Down
n
Drives Low Cost, Low Impedance Cables
n
Short-Circuit Protection on All Outputs
n
Thermal Shutdown Protection
n
Guaranteed Operation to 125°C
n
Industrial Control Data Networks
n
CAN Bus Applications
n
HVAC Controls
GND1
GND2
R
TERM
178591 TA01
RO1
RE1
DE1
DI1
LT1785
RO2
RE2
DE2
DI2
LT1785
V
CC1
V
CC2
R
TERM
TX
TX
RX
RX
RO
178591 TA02
DI
Y-Z

Summary of content (16 pages)