Taiwan Semiconductor Corporation SMA4S51AH

Overview

SMA4S51AH from Taiwan Semiconductor is a unidirectional 400W surface-mount transient voltage suppressor (TVS) diode with a 51V working stand-off voltage, 57.0–63.0V breakdown voltage at 1mA test current, and 82.8V clamping voltage at 4.8A peak pulse current; it is AEC-Q101 qualified and used in automotive power rail protection.

For engineers reviewing the SMA4S51AH datasheet, SMA4S51AH pinout, SMA4S51AH application, or SMA4S51AH equivalent, key selection criteria include unidirectional polarity, SOD-128 package thermal performance (R_θJL = 20°C/W), 175°C max junction temperature, and compliance with JESD201 Class 2 whisker resistance and RoHS/halogen-free requirements.

Technical Context

This TVS diode employs a glass-passivated silicon junction optimized for high-energy transient suppression on DC power lines. Its 10/1000μs waveform rating supports IEC 61000-4-5 Level 4 surge immunity when properly mounted on a 5mm × 5mm copper pad.

The device operates across –55°C to +175°C junction temperature range and exhibits a low V_BR temperature coefficient of 0.095%/°C, ensuring stable clamping behavior under thermal stress in engine bay or motor control environments.

Key Specifications

Pinout & Package

Package: SOD-128 - Surface-mount, flat-lead, unidirectional package with cathode band marking; 0.028g mass; UL 94V-0 molding compound; matte tin-plated leads compliant with J-STD-002 solderability.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SMAJ51A and SMBJ51A, the SMA4S51AH delivers lower clamping voltage (82.8V vs. ≥93.6V), superior thermal resistance (R_θJL = 20°C/W), and AEC-Q101 qualification-making it preferred for automotive and thermally demanding industrial deployments.

Availability

SMA4S51AH is available at Aetrix Electronics and suitable for automotive electronics, BLDC motor drives, battery management systems, and industrial LED lighting requiring stable component supply with full traceability and lifecycle support.

Supply support for SMA4S51AH 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

Taiwan Semiconductor Corporation (TSC) is a vertically integrated Taiwanese semiconductor manufacturer specializing in discrete power devices, TVS diodes, rectifiers, and MOSFETs for industrial and automotive markets.

The SMA4SxxAH series was designed specifically for AEC-Q101-compliant transient suppression in high-temperature, high-reliability DC power rails-including 48V automotive systems, motor controllers, and energy storage interfaces.

FAQ

What is the maximum clamping voltage of the SMA4S51AH under standard test conditions?

The SMA4S51AH has a maximum clamping voltage (V_C) of 82.8 V when subjected to a 10/1000 µs peak pulse current of 4.8 A at T_A = 25°C. This value is measured per JEDEC standards and reflects the upper limit of voltage seen by downstream circuitry during surge events. The SMA4S51AH maintains this clamping performance across its specified junction temperature range, making it suitable for high-stress automotive and industrial applications.

Is the SMA4S51AH suitable for bidirectional transient protection?

No, the SMA4S51AH is a unidirectional TVS diode, indicated by its single cathode band marking and specified electrical parameters (e.g., forward voltage V_F = 3.5 V @ 25 A). It is designed to clamp only reverse-polarity transients on positive-rail applications. For bidirectional protection, a separate symmetric device such as the SMA4S51AY (if offered) or dual-diode configuration would be required. The SMA4S51AH datasheet explicitly defines polarity as unidirectional.

What is the lead finish and solderability specification for the SMA4S51AH?

The SMA4S51AH features matte tin-plated leads that meet J-STD-002 solderability requirements. Its SOD-128 package is qualified for reflow and wave soldering processes, with moisture sensitivity level (MSL) rated at Level 1 per J-STD-020-meaning unlimited floor life at ≤30°C/60% RH. The device also passes JESD201 Class 2 whisker testing, ensuring long-term interconnect reliability in thermally cycled environments.

How does the thermal performance of the SMA4S51AH compare to standard SMAJ devices?

The SMA4S51AH offers significantly better thermal performance than legacy SMAJ-series TVS diodes: its junction-to-lead thermal resistance (R_θJL) is 20°C/W versus ~35°C/W for SMAJ, and its R_θJA is 62°C/W (measured on 5 mm × 5 mm Cu pad) versus 75°C/W for SMAJ51A. This enables higher sustained power handling and improved reliability in compact, high-temperature layouts. The SMA4S51AH's design directly addresses thermal limitations observed in earlier packages under continuous surge duty.

Does the SMA4S51AH require derating at elevated ambient temperatures?

Yes, the SMA4S51AH must be derated above T_A = 25°C per Figure 1 in the datasheet. Its non-repetitive peak impulse power (P_PPM) decreases linearly with rising ambient temperature, reaching ~50% of 400W at 100°C ambient. Derating is based on junction temperature limits (T_J ≤ 175°C) and assumes mounting on a 5 mm × 5 mm copper pad. Designers must apply thermal modeling or empirical testing to confirm safe operation in target enclosures. The SMA4S51AH's R_θJA = 62°C/W provides the basis for such calculations.