STMicroelectronics ST3485EIDT

Overview

ST3485EIDT from STMicroelectronics is a half-duplex, 3.3 V RS-485/RS-422 transceiver with ±15 kV IEC 61000-4-2 ESD protection, guaranteed 12 Mbps data rate, -40 °C to +125 °C operating temperature, and SO8 package. It integrates one driver and one receiver, supports up to 64 nodes on a bus, and features low-power shutdown (≤1 µA). It is used in industrial automation networks requiring robust differential communication in harsh environments.

For engineers reviewing the ST3485EIDT datasheet, ST3485EIDT pinout, ST3485EIDT application, or ST3485EIDT equivalent, key selection criteria include common-mode range (-7 to +12 V), driver short-circuit/thermal protection, receiver fail-safe output on floating inputs, interoperability with 5 V logic, and automotive-grade qualification per AEC-Q100.

Technical Context

The ST3485EIDT implements a half-duplex RS-485/RS-422 physical layer interface with independent DE (driver enable) and RE (receiver enable) control lines, enabling precise direction control. Its driver delivers ≥1.5 V differential output (VOD) into 54 Ω load and maintains ≤0.2 V change (∆VOD) across state transitions.

The receiver features a -0.2 V to +0.2 V differential threshold (VTH) with 70 mV hysteresis, guaranteed high-Z output during shutdown (RE = high, DE = low), and fail-safe operation-outputting logic high when A/B lines are unconnected or idle. Shutdown current is ≤1 µA at VCC = 3.6 V.

Key Specifications

Pinout & Package

ST3485EIDT uses an SO8 (Small Outline 8-pin) surface-mount package with standard 1.27 mm pitch, 5.0 mm × 6.2 mm body, and ECOPACK® environmental compliance.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX3485ESA+ and SN65HVD3485DR, ST3485EIDT uniquely combines automotive-grade temperature range (+125 °C), full IEC 61000-4-2 ESD compliance, and industrial bus robustness-making it the only option for mission-critical, high-temperature, or automotive-qualified RS-485 nodes.

Availability

ST3485EIDT is available at Aetrix Electronics and suitable for industrial PLC backplanes, automotive body control modules, smart energy metering, and factory automation HMI links requiring stable component supply across extended temperature and ESD stress conditions.

Supply support for ST3485EIDT 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, power ICs, sensors, and analog/mixed-signal products for industrial, automotive, and consumer markets.

The ST3485EIDT belongs to ST's RS-485/RS-422 transceiver product line, engineered specifically for high-noise, high-reliability wired communication in automotive ECUs and industrial control systems demanding extended temperature operation and certified ESD resilience.

FAQ

What is the maximum bus length supported by ST3485EIDT at 12 Mbps?

At its guaranteed 12 Mbps data rate, ST3485EIDT supports up to 15 meters of standard 120 Ω twisted-pair cable (e.g., Belden 9841). Longer distances require reduced data rates: 1200 meters is achievable at 100 kbps, per RS-485 specification constraints and signal integrity modeling using its 12 ns typical tTD transition time.

Does ST3485EIDT require external termination resistors?

Yes - ST3485EIDT does not integrate termination resistors. A 120 Ω resistor must be placed across the A and B bus lines at the farthest node(s) to prevent reflections. Stub lengths should be minimized (<15 cm), and point-to-point or daisy-chain topologies are recommended; star topologies require active repeaters.

How does the fail-safe receiver behave when the bus is disconnected?

When A and B inputs are open-circuit or shorted together, the ST3485EIDT receiver guarantees a logic-high RO output due to internal biasing. This prevents UART framing errors or spurious interrupts in microcontrollers, eliminating need for external pull-up/down resistors on RO in most designs.

Can ST3485EIDT be used with 5 V microcontrollers without level shifting?

Yes - ST3485EIDT logic inputs (DI, DE, RE) accept 0–5 V voltage levels and are fully 5 V tolerant, with VIH(min) = 2.0 V and VIL(max) = 0.8 V at VCC = 3.3 V. No external level shifters are needed when interfacing to 5 V GPIOs, simplifying design and reducing BOM count.