STMicroelectronics SM50T39AY

Overview

SM50T39AY from STMicroelectronics is an AEC-Q101-qualified unidirectional automotive TVS diode in SMC package, designed to clamp transient surges up to 5000 W (10/1000 µs) and 136 A peak pulse current while maintaining low leakage (0.2 µA at 25 °C) and high junction temperature capability (175 °C). It delivers 53.3 V clamping voltage at 94 A under 10/1000 µs waveform and supports ISO 7637-2 Pulse 1 (−150 V), Pulse 2a (+112 V), Pulse 3a (−220 V), and Pulse 3b (+150 V) protection in 12 V automotive power networks.

For engineers reviewing the SM50T39AY datasheet, SM50T39AY pinout, SM50T39AY application, or SM50T39AY equivalent, key selection criteria include its 39 V breakdown voltage (min 36.7 V, typ 38.6 V, max 40.5 V), unidirectional polarity, SMC package compatibility with IPC7531 footprint, and compliance with IEC 61000-4-2 (±30 kV ESD), ISO 10605 (±30 kV), and ISO 16750 load-dump requirements.

Technical Context

This TVS diode uses planar silicon technology to achieve stable reverse leakage and thermal robustness across −55 °C to +175 °C operating junction temperature. Its dynamic resistance of 49.2 mΩ enables precise clamping control during fast transients like ISO 7637-2 Pulse 3b.

The device operates as a shunt protector: under normal bias it presents high impedance (>1 GΩ at VRM = 33 V), but triggers avalanche conduction when reverse voltage exceeds VBR, limiting downstream voltage to VCL ≤ 53.3 V at 94 A (10/1000 µs). Temperature coefficients αT = 10 × 10⁻⁴ /°C allow accurate VBR and VCL derating above 25 °C.

Key Specifications

Pinout & Package

SM50T39AY is housed in a JEDEC-registered SMC (DO-214AB) surface-mount package with matte tin-plated leads. The package measures 5.55–6.25 mm × 7.75–8.15 mm × 2.45 mm max height and features a standard cathode bar marking for polarity identification.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar TVS diode applications.

Compared with SMAJ39A and TPSMD39A, SM50T39AY provides superior surge handling (5000 W vs. 400 W/3000 W), tighter clamping (53.3 V vs. 67.8 V/55.1 V), and guaranteed AEC-Q101 performance across full automotive temperature range - making it the only choice for mission-critical power rail protection.

Availability

SM50T39AY is available at Aetrix Electronics and suitable for automotive body electronics, ADAS camera modules, electric power steering systems, and infotainment head units requiring stable component supply across extended production lifecycles.

Supply support for SM50T39AY 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, specializing in automotive, industrial, and power management solutions with vertical manufacturing capabilities.

SM50T39AY belongs to the SM50TY series of planar TVS diodes engineered specifically for automotive-grade transient suppression in harsh environments - targeting ISO 7637-2, ISO 10605, and ISO 16750 compliance without derating.

FAQ

What is the maximum clamping voltage of SM50T39AY under ISO 7637-2 Pulse 3b?

Under ISO 7637-2 Pulse 3b (+150 V, 50 Ω source impedance), SM50T39AY clamps to ≤53.3 V at 94 A (10/1000 µs), verified per DS13895 Figure 16. This ensures downstream components see no more than 53.3 V, well below typical 60 V absolute maximum ratings of automotive power ICs.

Does SM50T39AY require derating at elevated ambient temperatures?

Yes - VBR and VCL increase with junction temperature at αT = 10 × 10⁻⁴ /°C. At 150 °C junction, VBR rises by 1.25× its 25 °C value (e.g., 38.6 V → ~48.3 V), and VCL scales similarly. Designers must use Equation 1 and 2 from DS13895 page 3 to calculate actual clamping at operating Tj.

Can SM50T39AY replace bidirectional TVS devices in CAN bus protection?

No - SM50T39AY is unidirectional and unsuitable for bidirectional signal lines like CAN H/L. Its cathode-anode configuration only protects positive transients on supply rails. For CAN, use SM50T39CAY (bidirectional variant) or dedicated low-capacitance CAN TVS such as ESDCAN03-2BM.

What is the recommended PCB footprint for SM50T39AY?

The manufacturer specifies an IPC7531-compliant SMC footprint: 5.11 mm pad length × 1.54 mm pad width × 3.14 mm center-to-center spacing, with 8.19 mm overall land pattern width. Copper area ≥4 cm² per lead reduces Rth(j-a) to <40 °C/W, critical for sustaining repeated 5000 W pulses.