LT1785 Datasheet, PDF (1/12 Pages) Linear Technology – 60V Fault Protected RS485/RS422 Transceivers

LT1785/LT1785A
LT1791/LT1791A
60V Fault Protected
RS485/RS422 Transceivers
FEATURES
s _{Protected from Overvoltage Line Faults to ±60V}
s _{Pin Compatible with LTC485 and LTC491}
s _{High Input Impedance Supports Up to 128 Nodes}
s _{No Damage or Latchup to ESD}
IEC-1000-4-2 Level 4: ±15kV Air Discharge
IEC-1000-4-2 Level 2: ±4kV Contact Discharge
s _{Controlled Slew Rates for EMI Emissions Control}
s _{Guaranteed High Receiver Output State for Floating,}
Shorted or Inactive Inputs
s _{Outputs Assume a High Impedance When Off or}
Powered Down
s _{Drives Low Cost, Low Impedance Cables}
s _{Short-Circuit Protection on All Outputs}
s _{Thermal Shutdown Protection}
U
APPLICATIO S
s _{Industrial Control Data Networks}
s _{CAN Bus Applications}
s _{HVAC Controls}
DESCRIPTIO
The LT^®1785/LT1791 are half-duplex and full-duplex dif-
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 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 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.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
RO1
RX
RE1
LT1785
DE1
DI1
TX
RO2
RX
RE2
LT1785
DE2
DI2
TX
V_CC1
R_TERM
GND1
V_CC2
R_TERM
GND2
1785/91 TA01
Normal Operation Waveforms at 250kBaud
RO
Y-Z
DI
1785/91 TA02
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