The STMicroelectronics ST485EXDR is a high-speed, low-power RS-485/RS-422 transceiver designed for robust differential data communication in industrial, commercial, and embedded applications. It is optimized for multipoint and long-distance serial communications, providing reliable data transfer over twisted-pair cabling while offering advanced features such as enhanced ESD protection, low electromagnetic emissions, and wide common-mode voltage operation. The device is suitable for both half-duplex and full-duplex configurations, enabling flexible system designs that require robust and noise-immune serial communication.

## Device Overview and Functionality

The ST485EXDR is an RS-485 compliant transceiver that allows bidirectional communication on a differential pair. It features an improved driver architecture that supports extended data rates up to 20 Mbps, ensuring high-speed data transmission for real-time control and communication applications. The receiver input is tolerant to ±15 kV ESD contact and ±8 kV air discharge, providing protection against electrostatic discharge in harsh industrial and commercial environments. The device is fully compatible with the TIA/EIA-485-A standard and offers a fail-safe receiver input that guarantees a defined logic output when the bus is idle, open, or shorted, eliminating the need for external biasing resistors.

## Electrical Characteristics

The ST485EXDR operates over a wide supply voltage range from 4.75 V to 5.25 V, accommodating nominal 5 V systems. The driver output differential voltage is typically ±1.5 V across a 54 Ω load, providing reliable signal levels over distances up to 1200 meters depending on cable type and data rate. Driver and receiver quiescent currents are low, typically 120 µA per channel, which supports energy-efficient designs. The driver short-circuit current limit protects the device in case of accidental line faults, while the receiver input hysteresis of 100 mV enhances noise immunity and prevents false triggering under high electromagnetic interference conditions.

## Timing and Performance

The ST485EXDR supports propagation delays typically around 32 ns for both driver and receiver paths, allowing high-speed operation with minimal signal skew. The driver rise and fall times are controlled to reduce electromagnetic interference (EMI) on the bus while preserving signal integrity. It supports data rates from DC up to 20 Mbps, making it suitable for a wide range of serial communication protocols, including Modbus, Profibus, and CAN-over-RS-485 implementations. The device maintains robust operation under wide common-mode voltage conditions ranging from -7 V to +12 V, allowing reliable communication in ground-shifted or noisy industrial networks.

## Thermal and Environmental Specifications

The ST485EXDR is specified for operation across the industrial temperature range of -40°C to +85°C. It can withstand transient thermal events and maintains reliable operation under extended environmental stress. The device dissipates minimal power due to its low quiescent current and is designed to operate without additional heat sinks in standard PCB layouts. Its thermal resistance ensures that self-heating does not compromise performance in densely populated circuits or in applications with limited airflow.

## Protection and Robustness

The ST485EXDR integrates multiple protection features to enhance system reliability. Inputs are protected against overvoltage and common-mode voltage excursions beyond standard RS-485 limits. ESD robustness conforms to IEC 61000-4-2 standards, with ±15 kV contact and ±8 kV air discharge protection. The device also exhibits high immunity to electrical fast transients (EFT) and surge events, making it suitable for industrial automation networks, motor control applications, and fieldbus communication in harsh environments. Short-circuit protection on the driver output and thermal shutdown mechanisms further safeguard the device against abnormal operating conditions.

## Mechanical and Packaging Details

The ST485EXDR is supplied in an 8-lead SOIC package with a 3.9 mm body width, providing a compact footprint compatible with automated assembly processes. The package facilitates efficient thermal dissipation and mechanical stability on the PCB. The pinout is designed for easy integration with standard RS-485 transceiver layouts, minimizing design complexity while ensuring reliable signal routing and isolation from adjacent circuitry. It is RoHS compliant, ensuring environmental safety and compliance with international standards for hazardous substances.

## Applications

This transceiver is ideal for industrial automation, programmable logic controllers (PLCs), building automation systems, and long-distance communication links where robust differential signaling is required. It is suitable for multipoint networks, data acquisition systems, and any environment requiring high-speed, noise-immune serial communication over twisted-pair cabling. Its combination of low-power operation, fast data rate capability, and extended ESD and EMI protection makes it an excellent choice for industrial-grade communication networks.

## Key Specifications Summary

* Device Type: RS-485/RS-422 Differential Transceiver
* Data Rate: Up to 20 Mbps
* Supply Voltage: 4.75–5.25 V
* Driver Differential Output Voltage: ±1.5 V typical into 54 Ω
* Driver Short-Circuit Protection: Yes
* Receiver Input Hysteresis: 100 mV typical
* Common-Mode Voltage Range: -7 V to +12 V
* ESD Protection: ±15 kV contact, ±8 kV air
* Propagation Delay: ~32 ns (driver and receiver)
* Operating Temperature: -40°C to +85°C
* Package: 8-lead SOIC, 3.9 mm width
* Quiescent Current: 120 µA typical per channel
* Standards Compliance: TIA/EIA-485-A
* RoHS Compliant: Yes

The ST485EXDR provides high-speed, low-power differential communication with extensive protection features, making it a reliable solution for industrial and commercial applications that demand robust, noise-resistant RS-485 and RS-422 networks.