STMicroelectronics STR485LVQT

Overview

STR485LVQT from STMicroelectronics is a half-duplex RS-485 transceiver with dual supply domains (VL = 1.65–3.6 V for logic, VCC = 3.0–3.6 V for bus), 20 Mbps high-speed or 250 kbps low-slew-rate operation selectable via SLR pin, fail-safe receiver, and ±16 kV IEC61000-4-2 air-gap ESD protection - deployed in industrial automation networks requiring robust long-haul serial communication.

For engineers reviewing the STR485LVQT datasheet, STR485LVQT pinout, STR485LVQT application, or STR485LVQT equivalent, this device supports critical design decisions involving voltage domain isolation (VL vs. VCC), slew-rate–dependent signal integrity over 1 km cables, thermal shutdown behavior under bus contention, and fail-safe logic state assurance during open/short/idle bus conditions.

Technical Context

The STR485LVQT integrates independent logic and bus supply domains to decouple I/O voltage compatibility (1.8 V or 3.3 V logic) from RS-485 bus drive capability (3.3 V). Its SLR pin configures driver output edge rate: 7 ns rise/fall time at 20 Mbps (SLR = GND/open) or 200 ns at 250 kbps (SLR = VL), directly impacting EMI and cable-length-limited timing margins.

Receiver features fail-safe biasing that guarantees high R output when A–B differential voltage is near zero (open, shorted, or terminated idle bus), with input thresholds VIT+ = –20 mV and VIT– = –130 mV and 70 mV hysteresis. Thermal shutdown activates at TJ = 165 °C, forcing driver outputs into high-Z to prevent latch-up during sustained bus faults.

Key Specifications

Pinout & Package

STR485LVQT is housed in a thermally enhanced DFN10 (3 mm × 3 mm, 0.5 mm pitch) package with exposed thermal pad (pin 6 = GND), optimized for PCB heat dissipation in dense industrial modules.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX13487EASA+ and SN65HVD72DR, STR485LVQT uniquely supports independent logic/bus supplies and user-selectable slew rate - enabling optimized signal integrity across both short high-speed and long low-speed RS-485 deployments without compromising ESD robustness or fail-safe reliability.

Availability

STR485LVQT is available at Aetrix Electronics and suitable for industrial automation, smart grid infrastructure, building management systems, and medical device serial interfaces requiring stable component supply across extended temperature and ESD stress conditions.

Supply support for STR485LVQT 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, MCU, power, and sensor solutions for industrial, automotive, and consumer markets.

The STR485 product line targets robust industrial communications, delivering RS-485 transceivers with integrated protection, dual-supply flexibility, and fail-safe operation for mission-critical wired networks.

FAQ

What is the minimum recommended decoupling capacitance for VL and VCC supplies?

STMicroelectronics specifies a minimum 0.1 µF ceramic capacitor placed as close as possible to each supply pin (VL and VCC), with an additional bulk capacitor of at least 1 µF nearby. This ensures stable operation during fast driver switching and prevents ground bounce-induced receiver misreads, especially at 20 Mbps.

Can the SLR pin be left unconnected, and what is the resulting data rate?

Yes, SLR may float, and the device defaults to high-speed mode (20 Mbps) due to internal biasing. However, ST recommends explicit connection - to GND for 20 Mbps or to VL for 250 kbps - to avoid noise-induced transitions and ensure deterministic slew rate selection in noisy industrial environments.

How does the fail-safe receiver behave when the bus is terminated but idle?

When the RS-485 bus is properly terminated (120 Ω across A–B) and driven neither high nor low, the differential voltage settles near 0 V. The STR485LVQT's receiver interprets this as a valid logic high (R = high) due to its –20 mV VIT+ threshold and built-in fail-safe biasing - ensuring UART receives consistent idle framing.

Is thermal shutdown reversible, and what is the recovery behavior?

Yes - thermal shutdown is fully reversible. When junction temperature exceeds 165 °C, the driver outputs go high-Z; recovery occurs only after temperature falls below 150 °C (15 °C hysteresis), preventing oscillation. No external reset or power cycle is needed, and receiver remains functional during shutdown.