STMicroelectronics SMM4F6.5A-TR

Overview

SMM4F6.5A-TR from STMicroelectronics is a unidirectional 400 W transient voltage suppression diode designed for primary-level surge protection in low-voltage DC power rails and signal lines. It features a 6.5 V standoff voltage (VRM), 7.5 V minimum breakdown voltage (VBR), 11.2 V clamping voltage at 35.7 A (10/1000 µs), 0.093 Ω dynamic resistance, and operates up to 175 °C junction temperature - deployed in automotive body control modules and industrial sensor interfaces.

For engineers reviewing the SMM4F6.5A-TR datasheet, SMM4F6.5A-TR pinout, SMM4F6.5A-TR application, or SMM4F6.5A-TR equivalent, key selection criteria include clamping performance under 10/1000 µs surges, thermal derating above 125 °C, low leakage (<1 μA at 85 °C), flat STmite Flat package compatibility with high-density PCB layouts, and IEC 61000-4-2 level 4 ESD robustness (±30 kV).

Technical Context

This TVS diode uses planar silicon technology to achieve stable VBR over temperature (αT = 6.1 × 10⁻⁴ /°C) and low leakage current across its full operating range (−55 °C to +175 °C). Its unidirectional configuration provides asymmetric clamping optimized for DC-biased lines where reverse conduction must be blocked until breakdown.

The STmite Flat package enables high thermal dissipation via copper pad coupling (Rth(j-a) drops to ~2.5 °C/W with 4 cm² copper per lead), while maintaining 0.85 mm profile for space-constrained applications. Pulse power capability de-rates linearly from 400 W at 25 °C to 160 W at 175 °C (10/1000 µs).

Key Specifications

Pinout & Package

STmite Flat surface-mount package: 2-terminal unidirectional device in ultra-thin 0.85 mm profile (D = 1.90 mm, E = 3.80 mm, L1 = 2.40 mm), compliant with IPC7531 footprint and JEDEC MO-263AC outline.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SMAJ6.5A and SMCJ6.5A, SMM4F6.5A-TR delivers identical clamping performance in a 66% lower profile package with superior thermal coupling to PCB copper, enabling higher sustained surge duty cycles in thermally dense automotive modules.

Availability

SMM4F6.5A-TR is available at Aetrix Electronics and suitable for automotive body electronics, industrial sensor nodes, smart metering systems, and USB-C peripheral protection requiring stable component supply across extended temperature and long-lifecycle programs.

Supply support for SMM4F6.5A-TR 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 technologies with vertical manufacturing and AEC-Q101 qualification capabilities.

SMM4F is part of ST's STmite Flat TVS portfolio, engineered specifically for high-reliability, low-profile surge protection in space- and thermal-constrained automotive and industrial applications where traditional DO-214 packages cannot meet mechanical or thermal targets.

FAQ

What is the maximum allowable surge current for SMM4F6.5A-TR under 8/20 µs waveform?

The SMM4F6.5A-TR supports 166 A peak pulse current under 8/20 µs waveform at 25 °C ambient, corresponding to its 2.5 kW peak pulse power rating. At 175 °C junction temperature, this derates to approximately 132 A due to thermal limitation of the silicon die and package interface.

Does SMM4F6.5A-TR require a heatsink for operation at 175 °C junction temperature?

No external heatsink is required. The STmite Flat package achieves Rth(j-a) ≈ 2.5 °C/W with ≥4 cm² copper area per lead on FR4 PCB, enabling direct thermal coupling to the board. At 160 W dissipation (10/1000 µs), this yields ~400 °C/W × 160 W = 400 °C rise - but actual junction rise is limited by pulse duration and thermal mass, staying within 175 °C with proper copper layout.

Can SMM4F6.5A-TR be used in bidirectional signal protection applications?

No - it is strictly unidirectional. For bidirectional protection (e.g., RS-485, CAN), ST recommends the complementary SMM4F6.5CA variant. Using SMM4F6.5A-TR on AC-coupled or symmetric signal lines risks forward conduction during negative half-cycles and potential latch-up or damage.

How does the 0.093 Ω dynamic resistance impact system-level surge immunity?

A dynamic resistance of 0.093 Ω limits voltage overshoot during fast transients: for a 35.7 A 10/1000 µs surge, IR drop adds only ~3.3 V to VBR, resulting in total clamping of 11.2 V. This ensures downstream 12 V-rated ICs remain within safe operating area without requiring additional series impedance or filtering.