Taiwan Semiconductor Corporation SMA4F21AH

Overview

SMA4F21AH from Taiwan Semiconductor is a unidirectional 400W surface-mount transient voltage suppressor (TVS) diode with a 21V working stand-off voltage, 23.5–25.9V breakdown range at 1mA, and 34.1V clamping voltage at 11.7A peak pulse current; used for overvoltage protection in BLDC motor drives and automotive battery management systems.

For engineers reviewing the SMA4F21AH datasheet, SMA4F21AH pinout, SMA4F21AH application, or SMA4F21AH equivalent, key selection criteria include clamping performance under 10/1000μs surge, thermal resistance (R_θJL = 20°C/W), unidirectional polarity, and AEC-Q101 qualification for automotive-grade reliability.

Technical Context

This TVS diode employs a glass-passivated silicon junction optimized for fast response to transient surges up to 400W (10/1000μs waveform). Its unidirectional configuration provides forward conduction capability with VF = 3.5V @ 25A, enabling bidirectional protection when paired with complementary devices.

Designed for PCB mounting on 5mm × 5mm copper pads, it delivers R_θJA = 62°C/W and R_θJC = 16°C/W, supporting operation from –55°C to +175°C junction temperature. Moisture sensitivity level is J-STD-020 Level 1, and lead finish meets J-STD-002 solderability requirements.

Key Specifications

Pinout & Package

Thin SMA package: surface-mount, unidirectional, cathode-banded device with two terminals (anode and cathode); molded compound rated UL 94V-0; matte tin-plated leads; weight ≈ 0.030 g.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SMAJ21A and SMBF21A, SMA4F21AH uniquely combines AEC-Q101 qualification, 34.1V clamping at 11.7A, and Thin SMA footprint-making it optimal for space-constrained, thermally demanding automotive and industrial TVS placements where reliability and predictability are non-negotiable.

Availability

SMA4F21AH is available at Aetrix Electronics and suitable for BLDC motor drives, automotive battery management systems, and industrial SMPS requiring stable component supply with full traceability and long-term lifecycle support.

Supply support for SMA4F21AH 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 semiconductor manufacturer specializing in discrete power devices, TVS diodes, rectifiers, and MOSFETs for automotive, industrial, and computing markets.

The SMA4FxxAH series was developed specifically to meet AEC-Q101 requirements for unidirectional transient suppression in harsh-environment automotive subsystems-including motor control, lighting, and battery monitoring-while maintaining compatibility with standard SMT assembly processes.

FAQ

What is the maximum clamping voltage of the SMA4F21AH under a 10/1000µs surge?

The SMA4F21AH has a maximum clamping voltage (V_C) of 34.1 V when subjected to a 10/1000 µs surge waveform at its rated peak pulse current of 11.7 A. This value is measured per JEDEC standards and confirmed in the official Taiwan Semiconductor datasheet revision C2103. The clamping performance ensures protected circuits remain within safe voltage limits during transient events. Designers should verify layout parasitics and trace inductance to maintain this clamping behavior in actual application.

Is the SMA4F21AH qualified for automotive applications?

Yes, the SMA4F21AH is AEC-Q101 qualified, meaning it has passed rigorous stress tests including high-temperature operating life, temperature cycling, and highly accelerated stress testing-specifically for discrete semiconductors used in automotive electronics. This qualification makes SMA4F21AH suitable for under-hood and cabin applications such as BLDC motor controllers and battery management systems where reliability under thermal and mechanical stress is mandatory.

What is the thermal resistance from junction to ambient for the SMA4F21AH?

The junction-to-ambient thermal resistance (R_θJA) of the SMA4F21AH is 62°C/W when mounted on a standard 5 mm × 5 mm copper pad test board. This value assumes natural convection and no additional heatsinking. For improved thermal performance, designers may increase copper area or add thermal vias-though R_θJL = 20°C/W indicates strong conduction through the leads into the PCB, making SMA4F21AH well-suited for compact, high-power-density layouts.

Does the SMA4F21AH have a unidirectional or bidirectional configuration?

The SMA4F21AH is a unidirectional TVS diode, indicated by its cathode band marking and specified forward voltage (V_F = 3.5 V @ 25 A). It conducts in forward bias like a standard diode and clamps in reverse bias during overvoltage events. Bidirectional protection requires either a separate SMA4F21AH paired with a series diode or a dedicated bidirectional part such as SMA4F21AY-SMA4F21AH itself does not provide symmetrical clamping.

What packaging and reel quantity is available for the SMA4F21AH?

The SMA4F21AH is supplied in Thin SMA package format on tape-and-reel, with 14,000 units per reel. This packaging supports high-speed automated SMT placement and complies with EIA-481 standards. The device's matte tin-plated leads meet J-STD-002 solderability requirements, and its J-STD-020 Level 1 moisture sensitivity eliminates the need for pre-bake prior to reflow. Aetrix Electronics maintains full traceability for all reels shipped.