STMicroelectronics ST485EXN

Overview

ST485EXN from STMicroelectronics is a half-duplex RS-485/RS-422 transceiver in SO-8 package, operating from a single 5 V supply with 300 µA quiescent current, ±15 kV HBM ESD protection, and -55°C to +125°C extended temperature range. It integrates one driver and one receiver for multipoint bus communication in industrial automation and building control systems.

For engineers reviewing the ST485EXN datasheet, ST485EXN pinout, ST485EXN application, or ST485EXN equivalent, key selection criteria include common-mode input range (-7 V to +12 V), 5 Mbps maximum data rate, 30 ns driver propagation delay, and thermal shutdown protection for driver overload resilience.

Technical Context

The ST485EXN implements a half-duplex transceiver architecture with independent driver enable (DE) and receiver enable (RE) controls, supporting bidirectional communication on shared differential buses. Its receiver features 70 mV typical hysteresis and operates across -7 V to +12 V common-mode voltage, enabling robust noise immunity in electrically noisy environments.

Driver outputs A and B are short-circuit current limited (250 mA peak) and protected by thermal shutdown, forcing high-impedance state under fault conditions. The device maintains high-impedance driver output when powered off or in 3-state mode, preventing bus contention during power sequencing or standby.

Key Specifications

Pinout & Package

ST485EXN is housed in an SO-8 (Small Outline, 8-pin) surface-mount package per JEDEC MS-012, with 1.27 mm pitch, 4.9 mm width, and 6.0 mm length. Pin 1 is marked by a beveled corner or dot.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar RS-485 transceiver applications.

Compared with MAX13487EESA+ and SN65HVD72DR, ST485EXN uniquely combines extended temperature operation (-55°C to +125°C), thermal shutdown, and 5 V-only supply in a cost-optimized SO-8 footprint-making it optimal for harsh-environment industrial nodes where reliability under fault and thermal stress is non-negotiable.

Availability

ST485EXN is available at Aetrix Electronics and suitable for industrial PLC communication, building automation networks, smart meter data concentrators, and railway signaling interfaces requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for ST485EXN includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, designing and manufacturing analog, mixed-signal, power, and microcontroller solutions for industrial, automotive, and consumer markets.

The ST485EXN belongs to ST's RS-485 transceiver product line, engineered specifically for robust, low-power, extended-temperature serial communication in harsh industrial environments where ESD resilience and bus fault tolerance are critical.

FAQ

What is the maximum number of ST485EXN transceivers supported on a single RS-485 bus?

The ST485EXN has a unit load of 1/8, meaning up to 256 devices can be connected on one bus segment without exceeding the RS-485 standard's 32-unit-load limit. This is achieved through high input resistance (96 kΩ) and low capacitive loading per receiver, enabling large-scale distributed control networks without repeaters.

Does ST485EXN require external current-limiting resistors on the A/B lines?

No. The ST485EXN integrates driver current limiting and thermal shutdown, eliminating the need for external series resistors on A/B lines. External 120 Ω termination resistors are still required at bus ends per RS-485 specification, but no additional current-limiting components are necessary for short-circuit protection.

Can ST485EXN operate with a 3.3 V supply?

No. ST485EXN is specified only for 5 V ±5 % operation. Its driver output voltage levels (VOD ≥1.5 V differential), input thresholds (VIH = 2.0 V), and internal biasing are designed exclusively for 5 V logic compatibility. Using 3.3 V will result in undefined behavior, insufficient drive strength, and possible failure to meet RS-485 electrical standards.

How does the ST485EXN handle bus contention during power-up or reset sequences?

During power-up, ST485EXN defaults to high-impedance driver and receiver states until VCC stabilizes. Both DE and RE inputs have weak internal pull-downs, ensuring drivers remain disabled and receivers inactive until firmware explicitly asserts control-preventing spurious bus transmissions or contention during cold start or brown-out recovery.