STMicroelectronics SM15T39A

Overview

SM15T39A from STMicroelectronics is a unidirectional transient voltage suppression (TVS) diode in SMC package, designed for IEC 61000-4-2 ESD protection (30 kV air/contact) and IEC 61000-4-4 surge immunity (4 kV level 4). It features 39 V breakdown voltage (V_BR = 33.3–41.0 V), 53.9 V clamping voltage at 28 A (10/1000 µs), and 1500 W peak pulse power. Used in DC power rail protection for industrial PLCs, telecom interfaces, and automotive body control modules.

For engineers reviewing the SM15T39A datasheet, SM15T39A pinout, SM15T39A application, or SM15T39A equivalent, key selection criteria include unidirectional polarity, low leakage (≤0.2 µA at 25 °C), high T_j capability (150 °C), SMC footprint compatibility, and verified IEC 61000-4-2/4-4 compliance - critical for robust overvoltage protection in harsh environments.

Technical Context

The SM15T39A employs planar junction technology to achieve stable V_BR temperature coefficient (α_T = 10.0 × 10⁻⁴/°C) and low dynamic resistance (R_D = 0.461 Ω at 25 °C). Its unidirectional configuration enables asymmetric clamping on positive transients only, with reverse standoff voltage (V_RWM) of 33.3 V and maximum peak pulse current (I_PP) of 28 A under 10/1000 µs waveform.

Thermal performance is optimized for high-reliability operation: junction-to-ambient thermal resistance (R_th(j-a)) drops to ~40 °C/W with 3.5 cm² copper area per lead, and it sustains 1250 W peak power at T_j = 150 °C. The device meets J-STD-020 MSL Level 1 and UL 497B (QVGQ2.E136224) for surge protection in safety-critical systems.

Key Specifications

Pinout & Package

SM15T39A is housed in an SMC (DO-214AB) surface-mount package measuring 7.75–8.15 mm × 5.55–6.25 mm × 2.45 mm max, with matte tin-plated leads compliant with IPC7531 footprint and JEDEC MO-136. Thermal pad design supports efficient heat dissipation via PCB copper pour.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SMBJ36A and P6SMB39A, SM15T39A delivers superior 1500 W surge handling and lowest leakage (0.2 µA), making it optimal for high-reliability industrial and automotive applications where thermal stability and long-term parametric drift matter.

Availability

SM15T39A is available at Aetrix Electronics and suitable for industrial PLC I/O protection, automotive body control modules, telecom power interfaces, and smart meter DC input stages requiring stable component supply across extended temperature and surge stress conditions.

Supply support for SM15T39A 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 silicon solutions for automotive, industrial, and power management markets since 1987.

The SM15T series belongs to ST's high-power TVS portfolio, engineered specifically for robust IEC 61000-4-2/4-4/5-compliant protection in space-constrained, high-temperature environments.

FAQ

What is the maximum clamping voltage of SM15T39A under a 10/1000 µs surge?

The maximum clamping voltage (V_CL) is 53.9 V at 28 A for a 10/1000 µs waveform, measured at T_amb = 25 °C. This value increases with junction temperature due to α_T = 10.0 × 10⁻⁴/°C, reaching ~57.5 V at T_j = 125 °C per datasheet Figure 5 and Equation 3.

Is SM15T39A suitable for bidirectional signal line protection?

No - SM15T39A is unidirectional and only protects against positive transients on the cathode line. For bidirectional protection (e.g., RS-485, USB), use SM15T39CA, which has symmetrical clamping in both polarities and identical V_BR and V_CL specs.

How does the SMC package affect thermal performance in high-density PCB layouts?

The SMC package achieves R_th(j-a) ≈ 40 °C/W with ≥3.5 cm² copper per lead (per Figure 12). In compact layouts, thermal relief must be minimized - solid copper pours under both leads and internal thermal vias are essential to sustain 1500 W pulses without exceeding T_j = 150 °C.

Does SM15T39A require derating at elevated ambient temperatures?

Yes - peak pulse power must be derated linearly above 25 °C per Figure 3: at T_j = 125 °C, P_PP drops to ~1250 W (10/1000 µs). System-level thermal modeling is required to ensure actual T_j stays ≤150 °C during worst-case surge repetition.