STMicroelectronics SMA4F31A

Overview

SMA4F31A from STMicroelectronics is a unidirectional 400 W transient voltage suppression (TVS) diode designed for primary-level surge protection in DC power rails and signal lines. It features a 31 V stand-off voltage (VRM), 37.8 V maximum clamping voltage at 50.2 A (10/1000 µs), 0.2 µA leakage at 25 °C, and operates up to 175 °C junction temperature - enabling robust ESD and lightning surge protection in industrial power supplies and automotive body electronics.

For engineers reviewing the SMA4F31A datasheet, SMA4F31A pinout, SMA4F31A application, or SMA4F31A equivalent, key selection criteria include clamping performance under IEC 61000-4-2 Level 4 (±25 kV contact / ±30 kV air), thermal derating above 100 °C, unidirectional polarity compatibility with grounded-return systems, and SMA package footprint compliance with IPC7531.

Technical Context

The SMA4F31A employs planar silicon avalanche technology optimized for low-leakage, high-temperature reliability in long-life applications. Its breakdown voltage is tightly specified at 34.2–37.8 V (min–max at 1 mA), with dynamic resistance of 0.77 Ω enabling predictable clamping behavior across pulse durations from 10 µs to 1000 µs.

It meets IEC 61000-4-2 Level 4 ESD immunity and supports peak pulse power up to 200 W at Tj = 175 °C (10/1000 µs), making it suitable for circuits where thermal management is constrained and sustained surge energy must be absorbed without parametric shift.

Key Specifications

Pinout & Package

The SMA4F31A is housed in an industry-standard SMA (DO-214AC) flat plastic package with matte tin-plated leads, compliant with IPC7531 footprint and JEDEC MO-136AB outline. Package dimensions: 4.6 mm × 2.9 mm × 2.3 mm (L × W × H), with 2.3 mm lead spacing and 0.9 mm lead thickness.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SMAJ33A and SMBJ33A, the SMA4F31A offers tighter clamping (50.2 V vs. 53.3 V) and lower leakage (0.2 µA vs. 0.5 µA), making it preferable for 31 V nominal rails and battery-powered systems where leakage-induced drain must be minimized.

Availability

SMA4F31A is available at Aetrix Electronics and suitable for industrial power supplies, automotive body electronics, smart metering, and outdoor LED lighting requiring stable component supply across multi-year production cycles.

Supply support for SMA4F31A 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 management solutions with vertical manufacturing and broad analog/mixed-signal IP.

The SMA4F Transil series targets high-reliability transient suppression in harsh-environment applications, emphasizing low leakage, high-temperature stability, and IEC/UL-certified surge performance for mission-critical infrastructure.

FAQ

What is the maximum peak pulse current the SMA4F31A can handle?

The SMA4F31A sustains 50.2 A peak pulse current under the 10/1000 µs waveform at 25 °C ambient, with clamping voltage limited to 50.2 V. At elevated junction temperatures (e.g., 175 °C), its peak pulse power derates to 200 W, corresponding to approximately 35 A under the same waveform - verified per Figure 3 in DS12542 Rev 1.

Is the SMA4F31A suitable for bidirectional signal line protection?

No - the SMA4F31A is strictly unidirectional, with cathode marking indicating polarity-sensitive installation. For bidirectional protection (e.g., USB data lines or RS-485), ST recommends the SMA4F31AY variant or discrete back-to-back diode configurations; using SMA4F31A on AC-coupled signals risks forward conduction and latch-up.

How does the SMA4F31A's clamping voltage change with temperature?

VCL increases with junction temperature at a coefficient of +9.9 × 10⁻⁴/°C (αT), per Table 2 footnote 2. At 125 °C, VCL rises ~10% versus 25 °C - e.g., from 50.2 V to ~55.2 V at 50.2 A. This is fully characterized and accounted for in ST's thermal derating curves (Figure 3).

Can the SMA4F31A replace SMAJ30A in existing designs?

Yes, with verification: SMA4F31A has 31 V VRM vs. SMAJ30A's 30 V, and clamps at 50.2 V vs. 48.4 V - a +1.8 V increase that may exceed downstream IC ratings. Its lower leakage (0.2 µA vs. 1 µA) improves low-power performance, but layout must confirm SMA footprint compatibility and thermal relief copper area per Figure 11.