STMicroelectronics SM6T39A

Overview

SM6T39A from STMicroelectronics is a unidirectional transient voltage suppression (TVS) diode in SMB package, designed to clamp ESD and surge transients on signal/power lines. It delivers 600 W peak pulse power (10/1000 µs), clamps at 53.9 V (max) under 11.1 A IPP, and maintains low leakage (≤0.2 µA @ 25 °C) for high-reliability SMPS and industrial I/O protection.

For engineers reviewing the SM6T39A datasheet, SM6T39A pinout, SM6T39A application, or SM6T39A equivalent, key selection criteria include clamping voltage (V_CL), breakdown voltage range (33.3–41.0 V), junction temperature capability (−55 to +150 °C), dynamic resistance (0.504 Ω), and UL497B recognition for isolated loop circuits.

Technical Context

The SM6T39A operates as a silicon avalanche diode with planar junction technology, enabling stable breakdown behavior and low leakage across −55 to +150 °C junction temperature. Its unidirectional configuration provides forward conduction path only during reverse overvoltage events, supporting polarity-sensitive interfaces like RS-485 or CAN bus receivers.

Clamping performance is defined by V_CL = V_BR(max) + R_D × I_PP, where R_D = 0.504 Ω ensures tight voltage control under 11.1 A transient current. The device meets IEC 61000-4-2 level 4 (30 kV air/contact discharge) and IEC 61000-4-4 level 4 (4 kV), with UL497B recognition for isolated loop circuit protection.

Key Specifications

Pinout & Package

SMB (DO-214AA) surface-mount package: 3.3–3.95 mm length, 5.1–5.6 mm width, 1.9–2.45 mm height, matte tin-plated leads compliant with J-STD-020 MSL level 1 and IPC7531 footprint.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar transient suppression applications.

Compared with SMAJ39A and 1.5SMC39A, SM6T39A offers optimal balance of clamping accuracy (53.9 V), low dynamic resistance (0.504 Ω), and UL497B certification-making it preferred for space-constrained, safety-certified industrial I/O modules where precise voltage limiting and regulatory compliance are critical.

Availability

SM6T39A is available at Aetrix Electronics and suitable for industrial PLC I/O protection, automotive body control modules, telecom power interface hardening, and medical sensor signal line ESD suppression requiring stable component supply across extended production lifecycles.

Supply support for SM6T39A 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, delivering innovative solutions across automotive, industrial, and power management markets with strong IP and manufacturing vertical integration.

The SM6T series belongs to ST's high-reliability TVS portfolio, engineered specifically for low-leakage, high-temperature stability, and regulatory-compliant transient protection in mission-critical industrial and automotive electronics.

FAQ

What is the maximum clamping voltage of SM6T39A under a 10/1000 µs surge?

The maximum clamping voltage (V_CL) of SM6T39A is 53.9 V when subjected to an 11.1 A peak pulse current (I_PP) with a 10/1000 µs waveform. This value is measured at T_amb = 25 °C and reflects worst-case clamping performance under standardized surge conditions per IEC 61000-4-5.

Does SM6T39A meet automotive-grade reliability standards?

SM6T39A is qualified per AEC-Q101 for discrete semiconductors and supports automotive applications including body control modules and LIN bus protection. Its −55 to +150 °C operating junction temperature range, UL497B recognition, and IEC 61000-4-2/4-4 compliance align with functional safety requirements for non-safety-critical automotive subsystems.

How does the dynamic resistance affect real-world clamping performance?

With a dynamic resistance (R_D) of 0.504 Ω, SM6T39A adds minimal voltage overshoot beyond its base breakdown voltage during transient events. For example, at 10 A surge current, the additional clamping rise is just 5.04 V-enabling tighter voltage margins than alternatives with R_D > 0.7 Ω, especially critical for 3.3 V or 5 V logic interfaces.

Can SM6T39A be used in bidirectional signal lines like RS-485?

No-SM6T39A is unidirectional and must be used with correct polarity: cathode toward the protected line, anode to ground. For bidirectional data lines such as RS-485, the bidirectional variant SM6T39CA is required, which clamps symmetrically for both positive and negative transients without polarity constraints.