STMicroelectronics SM15T33A

Overview

SM15T33A 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 a 33 V breakdown voltage (V_BR = 28.2–34.7 V), 45.7 V clamping voltage at 1 A (V_CL), and 1500 W peak pulse power (10/1000 µs) at T_j = 25 °C. Used in DC power rails of industrial PLCs, telecom interfaces, and automotive body control modules.

For engineers reviewing the SM15T33A datasheet, SM15T33A pinout, SM15T33A application, or SM15T33A equivalent, key selection criteria include unidirectional polarity, low leakage (≤0.2 µA at 25 °C), high junction temperature rating (T_j,max = 150 °C), and SMC package compatibility with FR4 PCBs using IPC7531 footprint.

Technical Context

The SM15T33A employs planar silicon avalanche technology to deliver precise, repeatable clamping during fast transients. Its dynamic resistance (R_D = 0.333 Ω) ensures minimal voltage overshoot under 8/20 µs surges up to 169 A, while thermal impedance (Z_th(j-a)) remains stable across pulse durations from 0.1 s to 1000 s on standard FR4 layouts.

It operates as a shunt protector: reverse-biased between line and ground, conducting only when V_R exceeds V_BR, thereby diverting surge current away from downstream ICs. The device maintains ≤1 µA leakage at V_RM = 26.4 V and supports solder reflow per J-STD-020 MSL level 1 (260 °C peak, 10 s).

Key Specifications

Pinout & Package

SM15T33A uses the SMC (DO-214AB) surface-mount package: 2-terminal, unidirectional configuration with cathode marked by band. Dimensions per JEDEC MS-012: length 7.75–8.15 mm, width 5.55–6.25 mm, height 2.45 mm max. Matte tin-plated leads meet J-STD-002 and RoHS requirements.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SMBJ33A and 1.5KE33A, SM15T33A delivers 2.5× higher peak power in an SMT-optimized package with tighter V_CL tolerance and guaranteed low-leakage performance-critical for long-life, high-reliability embedded systems.

Availability

SM15T33A is available at Aetrix Electronics and suitable for industrial PLC I/O protection, automotive body control modules, and telecom power supply inputs requiring stable component supply, full traceability, and lifecycle continuity.

Supply support for SM15T33A 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 devices, sensors, and protection components for industrial, automotive, and consumer markets.

The SM15T series belongs to ST's high-power TVS portfolio, engineered specifically for robust front-end surge and ESD protection in harsh electromagnetic environments-emphasizing low leakage, high T_j capability, and standardized SMC packaging.

FAQ

What is the maximum clamping voltage of SM15T33A under a 100 A 8/20 µs surge?

Per DS0683 Rev 8 Figure 5, SM15T33A clamps to approximately 52.5 V at 100 A (8/20 µs). This value is derived from the V_CL–I_PP curve and accounts for dynamic resistance (R_D = 0.333 Ω) and temperature coefficient effects at T_j ≈ 85 °C during pulse application.

Can SM15T33A be used in bidirectional signal lines like RS-485?

No-SM15T33A is unidirectional and must be paired with a second device or replaced with SM15T33CA for bidirectional protection. Using SM15T33A alone on a differential bus risks forward conduction during negative transients, potentially damaging line drivers or receivers.

Does SM15T33A require derating at elevated ambient temperatures?

Yes-its peak pulse power drops linearly with junction temperature: at T_j = 125 °C, P_PP is reduced to ~1250 W (10/1000 µs) per Figure 3. Layout must ensure thermal resistance R_th(j-a) ≤ 120 °C/W (per Figure 12) to maintain reliability at full rating.

Is the SMC package of SM15T33A compatible with standard reflow soldering profiles?

Yes-SM15T33A meets J-STD-020 MSL level 1 and is qualified for peak reflow temperatures up to 245 °C for 20–30 seconds. ST's recommended profile (Figure 21) specifies ramp rates ≤3 °C/s, soak at 150–200 °C for 60–120 s, and controlled cooling to avoid solder joint voiding or package cracking.