STMicroelectronics ST485ABN

Overview

ST485ABN from STMicroelectronics is a half-duplex RS-485/RS-422 transceiver in DIP-8 package, featuring 30 Mbps max data rate, ±4 kV ESD protection, -7 to +12 V common-mode input range, and 5 mA max supply current. It integrates one driver and one receiver for industrial bus communication with thermal shutdown and fail-safe receiver logic.

For engineers reviewing the ST485ABN datasheet, ST485ABN pinout, ST485ABN application, or ST485ABN equivalent, key selection criteria include high-speed differential signaling capability, low-power shutdown mode (RE high + DE low), fail-safe open-circuit receiver behavior, and robust driver short-circuit/thermal protection.

Technical Context

The ST485ABN implements a single-ended logic interface (DI, RE, DE) controlling a differential driver (A/B) and receiver (RO), with independent enable control for each function. Its receiver includes 70 mV typical hysteresis and guaranteed logic-high output under open-wire conditions.

Driver operation supports short-circuit current limiting (±250 mA) and automatic thermal shutdown that forces A/B into high-impedance state. The device operates from a single 4.75–5.25 V supply and maintains functional integrity across -40°C to +85°C ambient temperature.

Key Specifications

Pinout & Package

DIP-8 package with through-hole mounting; 0.3-inch body width; lead-free ECOPACK® compliant; JEDEC MS-001AC mechanical standard.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX485CPA+ and SN65HVD72DR, the ST485ABN delivers balanced performance: higher speed than legacy parts without demanding layout constraints of ultra-high-speed variants, while offering superior fault protection and fail-safe behavior for industrial reliability.

Availability

ST485ABN is available at Aetrix Electronics and suitable for industrial PLC networks, building automation systems, energy metering gateways, and factory floor test equipment requiring stable component supply and long-term manufacturability.

Supply support for ST485ABN 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 microcontrollers, analog ICs, power devices, and sensors for industrial, automotive, and consumer markets.

The ST485ABN belongs to ST's RS-485/RS-422 transceiver product line, engineered specifically for robust, low-power, high-speed industrial communications in harsh electromagnetic environments.

FAQ

What is the minimum supply voltage required for reliable operation of the ST485ABN?

The ST485ABN operates reliably from 4.75 V to 5.25 V. Operation below 4.75 V is not guaranteed per datasheet specifications: driver output swing degrades, receiver threshold accuracy drifts, and thermal shutdown may become non-functional. For 5 V nominal systems, ensure regulator tolerance and PCB trace drop maintain VCC ≥4.75 V under full load.

Does the ST485ABN support full-duplex communication?

No, the ST485ABN is strictly a half-duplex transceiver with one driver and one receiver sharing the same A/B bus terminals. Full-duplex operation requires separate driver and receiver pairs (e.g., ST3485 or isolated dual-channel transceivers). Attempting full-duplex use will cause bus contention and signal corruption.

How does the fail-safe feature behave when the A and B lines are shorted together?

When A and B are shorted, the differential input voltage is 0 V, which falls within the receiver's undefined region (|VID| < 0.2 V). However, the internal fail-safe bias network pulls RO high regardless-ensuring a defined logic state. This behavior is confirmed in Table 4 (Truth table – receiver) and applies to both open and shorted line conditions.

Can the ST485ABN be used without external termination resistors?

Yes, but only for short bus runs (<10 m) at ≤10 Mbps. For longer distances or higher data rates, a 120 Ω termination resistor must be placed at each bus end to prevent reflections. The ST485ABN itself does not integrate termination; omission in multi-drop or long-cable deployments causes signal ringing and bit errors, especially above 10 Mbps.