LT1785

PRODUCTION

60V Fault Protected RS485/RS422 Transceivers

Data Sheet (Rev. E) Product Selection Table
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Overview

  • 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
    • IEC-1000-4-2 Level 4: ±15kV Air Discharge
    • 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
  • AEC-Q100 Qualified for Automotive Applications (LT1785#W)

The LT1785/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 outputs control 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.

Applications

  • Industrial Control Data Networks
  • CAN Bus Applications
  • HVAC Controls 
LT1785
60V Fault Protected RS485/RS422 Transceivers
LT1785-1785A-1791-1791A Application Circuit LT1785-1785A-1791-1791A Performance Graph LT1785-1785A Pin configuration LT1791-1791A Pin configuration
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Documentation

Data Sheet 1

Reliability Data 1

User Guide 1

Design Note 1

Technical Articles 3

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Hardware Ecosystem

Parts Product Life Cycle Description
Interface Transceivers 1
LTC2862
PRODUCTION ±60V Fault Protected 3V to 5.5V RS485/RS422 Transceivers
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Tools & Simulations

IBIS Model 1

Evaluation Kits

eval board
schematic 1
EVAL-RS485HDEBZ

Standard RS-485 Half-Duplex Evaluation Board, EVAL-RS485HDEBZ

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Product Details

The EVAL-RS485HDEBZ allows quick and easy evaluation of half-duplex RS-485 transceivers with standard 8-lead SOIC footprints. The evaluation board allows interfacing via screw terminal block to digital I/O for driver input (DI), receiver output (RO), driver enable (DE) and receiver output (RO). Bus signals A and B (half-duplex bus) can be connected to a bus screw terminal block. One or two termination resistors can be connected to A and B via jumper settings, in order to evaluation the half-duplex RS-485 driver and receiver. Footprints are provided for pull-up and pull-down (biasing resistors) on the bus.

Devices for evaluation on the board must be ordered separately.
EVAL-RS485HDEBZ
Standard RS-485 Half-Duplex Evaluation Board, EVAL-RS485HDEBZ
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Latest Discussions

1 Years Ago
When transmitter is disabled, on LT1785, there is current source pulling the -DATA pin to VCC through a 100Ω resistor to ground. I replaced the 1785 with a ST4E1240DT and the 100Ω pulled the -DATA pin to ~300mV. Changing back to the 1785 my problem ret
2 Years Ago
Interceptor Request
2 Years Ago
leakage through negative input protection diode
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