Features and Benefits
- 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.
- Industrial Control Data Networks
- CAN Bus Applications
- HVAC Controls
Product Lifecycle Production
At least one model within this product family is in production and available for purchase. The product is appropriate for new designs but newer alternatives may exist.
Evaluation Kits (1)
The EVAL-RS485FDEBZ allows quick and easy evaluation of full-duplex RS-485 transceivers with standard 14-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, B, Y and Z (full-duplex bus) can be connected to a bus screw terminal block. Termination resistors are fitted across A and B, as well as Y and Z. These can be connected in half-duplex configuration (A to Y, B to Z), in order to evaluate the RS-485 driver. Footprints are provided for pull-up and pull-down (biasing resistors) on the receiver inputs in order to provide the option to evaluate an RS-485 receiver with this configuration.
Devices for evaluation on the board must be ordered separately.
Documentation & Resources
R001 Reliability Data3/23/201821K
DN203 - RS485 Transceivers Sustain ±60V Faults7/15/201490K
RS485 Quick Guide7/13/2017524K
Ultra Rugged ±60V RS485 Transceivers3/15/2013282K
Digital Isolation and Interface Technology Selection Guide2/7/20204 M
RS485/RS422 Transceivers Operate from 3V to 5.5V Supplies and Withstand ±60V Faults4/1/2014 LT Journal
LT1785 and LT1791: 60V, Fault-Tolerant RS485/RS422 Transceivers6/1/1999 LT Journal
Tools & Simulations
LT1791 Companion Parts
Recommended Related Parts
ADI has always placed the highest emphasis on delivering products that meet the maximum levels of quality and reliability. We achieve this by incorporating quality and reliability checks in every scope of product and process design, and in the manufacturing process as well. "Zero defects" for shipped products is always our goal.View our quality and reliability program and certifications for more information.
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Pricing displayed is based on 1-piece. The USA list pricing shown is for budgetary use only, shown in United States dollars (FOB USA per unit), and is subject to change. International prices may vary due to local duties, taxes, fees and exchange rates.