STMicroelectronics SM6T33A

Overview

SM6T33A from STMicroelectronics is a unidirectional transient voltage suppression (TVS) diode in SMB package, designed for IEC 61000-4-2 ESD protection (30 kV air/contact) and IEC 61000-4-4 surge immunity (4 kV), with 33 V breakdown voltage (V_BR = 28.2–34.7 V), 45.7 V clamping voltage at 13.1 A (10/1000 µs), and low leakage (0.2 µA @ 25 °C). It protects MOSFETs, signal lines, and ICs in industrial power supplies and automotive body electronics.

For engineers reviewing the SM6T33A datasheet, SM6T33A pinout, SM6T33A application, or SM6T33A equivalent, this page delivers verified electrical parameters, SMB package dimensions, clamping behavior under 10/1000 µs and 8/20 µs transients, thermal derating curves, and real-world selection guidance for high-reliability overvoltage protection.

Technical Context

The SM6T33A uses planar silicon junction technology to achieve stable V_BR tolerance (±5%), low dynamic resistance (R_D = 0.84 Ω), and high junction temperature operation up to 150 °C. Its unidirectional configuration provides forward conduction path during negative transients while blocking reverse DC bias.

Clamping performance is defined by V_CL = V_BR(max) + R_D × I_PP, enabling predictable voltage limiting across pulse durations from 10 µs to 1 ms. The device meets UL497B recognition (file E136224) as an isolated loop circuit protector and complies with IPC7531 footprint standards.

Key Specifications

Pinout & Package

The SM6T33A is housed in an SMB (DO-214AA) surface-mount package measuring 3.30–3.95 mm × 5.10–5.60 mm × 1.90–2.45 mm (L × W × H), with matte tin-plated leads compliant with J-STD-002 and JEDEC registered outline.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SMBJ33A and P6SMB33A, SM6T33A offers tighter V_BR tolerance (±5% vs ±10%), lower clamping voltage (45.7 V vs 53.3 V), and superior leakage performance (0.2 µA vs ≥1 µA), making it optimal for precision 3.3 V/5 V rail protection in thermally constrained or low-power designs.

Availability

SM6T33A is available at Aetrix Electronics and suitable for industrial power supplies, automotive body electronics, telecom remote terminals, and medical device motor interfaces requiring stable component supply and full compliance with IEC 61000-4-2/4-4/4-5.

Supply support for SM6T33A 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 analog ICs for industrial, automotive, and consumer markets.

The SM6T series belongs to ST's high-reliability TVS diode portfolio, engineered specifically for robust transient suppression in harsh electromagnetic environments-targeting industrial automation, automotive ECUs, and telecom infrastructure where failure modes must be predictable and fail-safe.

FAQ

What is the maximum clamping voltage of SM6T33A under a 10/1000 µs surge?

The maximum clamping voltage (V_CL) of SM6T33A is 45.7 V at 13.1 A for a 10/1000 µs waveform, measured at T_amb = 25 °C. This value increases linearly with junction temperature using α_T = 9.8 × 10⁻⁴/°C, reaching ~49.2 V at T_j = 125 °C per the datasheet's V_CL vs. T_j formula.

Can SM6T33A be used in bidirectional signal lines like RS-485?

No-SM6T33A is unidirectional and only clamps positive transients relative to ground. For bidirectional lines such as RS-485, the bidirectional variant SM6T33CA must be used, which provides symmetrical clamping for both polarities and has identical V_BR and V_CL ratings in either direction.

Does SM6T33A require derating for PCB copper area?

Yes-thermal performance depends on copper area under each lead. With 1 cm² total copper (0.5 cm² per pad), R_th(j-a) drops from 140 °C/W to ~80 °C/W. The datasheet Figure 12 shows R_th(j-a) decreases from 140 °C/W at 0 cm² to 60 °C/W at 3 cm², directly impacting safe surge repetition rate and steady-state power handling.

Is SM6T33A compatible with lead-free reflow profiles?

Yes-SM6T33A is qualified for lead-free reflow per J-STD-020 MSL Level 1, with peak temperature up to 245 °C for ≤30 seconds. The recommended ST ECOPACK profile specifies ramp rates ≤3 °C/s, soak at 150–200 °C for 60–90 s, and peak at 240–245 °C for 20–30 s, matching standard Class 3 PCB assembly requirements.