STMicroelectronics SM6T68A

Overview

SM6T68A from STMicroelectronics is a unidirectional transient voltage suppression (TVS) diode in SMB package, designed for IEC 61000-4-2 ESD and IEC 61000-4-4 surge protection of signal lines and power rails. It features a 68 V breakdown voltage (V_BR = 68 V), 92 V clamping voltage at 6.5 A (V_CL = 92 V, I_PP = 6.5 A, 10/1000 µs), 600 W peak pulse power, and low leakage current (0.2 µA @ 25 °C). It is used in industrial PLC I/O modules to protect RS-485 transceivers against lightning-induced surges.

For engineers reviewing the SM6T68A datasheet, SM6T68A pinout, SM6T68A application, or SM6T68A equivalent, this page delivers verified electrical parameters, SMB package layout, real-world clamping behavior under 10/1000 µs and 8/20 µs transients, thermal derating curves up to 150 °C junction temperature, and validated alternatives for ESD-hardened analog front-ends and DC power input stages.

Technical Context

The SM6T68A employs planar silicon junction technology optimized for low leakage (<0.2 µA @ 25 °C) and stable V_BR drift (α_T = 10.4 × 10⁻⁴/°C), enabling reliable operation up to T_j = 150 °C. Its dynamic resistance (R_D = 1.503 Ω) ensures tight clamping during fast transients.

It complies with UL497B (file E136224) as an isolated loop circuit protector and exceeds IEC 61000-4-2 level 4 (30 kV air/contact discharge) and IEC 61000-4-4 level 4 (4 kV), making it suitable for harsh industrial environments where sustained overvoltage immunity and solderability (MSL Level 1, 260 °C lead temp.) are critical.

Key Specifications

Pinout & Package

The SM6T68A is a two-terminal unidirectional TVS diode in SMB (DO-214AA) package. Cathode is marked by a band on the body; anode is unmarked. The device mounts with cathode connected to protected line and anode to ground reference.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SMAJ68A and 1.5SMC68A, SM6T68A delivers optimal balance of 600 W surge handling, 92 V clamping, SMB footprint compatibility, and low-leakage performance - making it preferred for space-constrained industrial I/O where precision and reliability coexist.

Availability

SM6T68A is available at Aetrix Electronics and suitable for industrial PLC analog input protection, RS-485 transceiver line hardening, DC power rail surge suppression, and smart sensor signal conditioning requiring stable component supply across extended temperature and long-lifecycle programs.

Supply support for SM6T68A 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 discrete solutions with vertical manufacturing and broad IP portfolio.

The SM6T series belongs to ST's industrial-grade TVS portfolio, engineered specifically for high-reliability surge and ESD protection in harsh environments-emphasizing low leakage, thermal stability, and standards-compliant robustness for factory automation and process control systems.

FAQ

What is the maximum clamping voltage of SM6T68A under a 10/1000 µs surge?

The SM6T68A clamps to 92 V at 6.5 A under 10/1000 µs waveform (Table 2, DS0684 Rev 15). This value is measured at T_amb = 25 °C and scales with junction temperature using α_T = 10.4 × 10⁻⁴/°C. At T_j = 125 °C, V_CL rises to approximately 98.5 V, remaining well below typical 100 V IC absolute maximum ratings.

Is SM6T68A suitable for bidirectional signal line protection?

No - SM6T68A is unidirectional and must be used with cathode toward the protected line and anode to ground. For true bidirectional protection (e.g., USB, RS-232), the bidirectional variant SM6T68CA is required. Using SM6T68A on AC-coupled or floating lines may result in forward conduction and failure during negative transients.

How does SM6T68A compare to SMAJ68A in terms of thermal performance?

SM6T68A sustains 350 W peak power at T_j = 150 °C (Figure 3), whereas SMAJ68A derates to ~250 W at same temperature. This 40% higher thermal capability stems from SM6T's planar junction design and optimized thermal resistance (R_th(j-a) ≈ 120 °C/W on standard FR4), enabling longer surge hold time in thermally constrained layouts.

Does SM6T68A require derating for elevated ambient temperatures?

Yes - its 600 W rating applies only at T_amb = 25 °C. Derating follows Figure 3: at 85 °C ambient, maximum PPP drops to ~420 W; at 125 °C, it falls to ~280 W. Designers must verify worst-case junction temperature using R_th(j-a), copper area, and pulse repetition rate to avoid thermal runaway during repetitive surges.