Vishay General Semiconductor - Diodes Division SMAJ18AHE3_A/I

Overview

SMAJ18AHE3_A/I from Vishay General Semiconductor is a unidirectional transient voltage suppressor (TVS) diode in SMA (DO-214AC) package, designed for robust overvoltage protection of sensitive electronics. It features a 18 V standoff voltage (V_WM), 20.0–22.1 V breakdown voltage (V_BR at 1 mA), 29.2 V maximum clamping voltage (V_C) at 13.7 A peak pulse current, and 400 W peak pulse power rating (10/1000 μs waveform). It is AEC-Q101 qualified and used to protect MOSFETs, ICs, and sensor signal lines in automotive and industrial power supply rails.

For engineers reviewing the SMAJ18AHE3_A/I datasheet, SMAJ18AHE3_A/I pinout, SMAJ18AHE3_A/I application, or SMAJ18AHE3_A/I equivalent, key selection criteria include its unidirectional polarity, 1.0 μA max reverse leakage at V_WM, -55 °C to +150 °C operating junction temperature range, and compliance with UL 497B for surge protector classification.

Technical Context

This TVS diode operates as a clamping device that remains high-impedance below V_WM = 18 V and rapidly transitions to low-impedance conduction above V_BR (min 20.0 V) to limit transient energy. Its glass-passivated junction ensures stable breakdown characteristics and fast response time (<1 ps), enabling effective suppression of ESD, lightning-induced surges, and inductive switching spikes.

The device is rated for 400 W peak pulse power (10/1000 μs) on standard 0.2" × 0.2" copper pads, derating to 300 W above 78 V, and supports repetitive surge events at 0.01% duty cycle. Thermal resistance is R_θJA = 120 °C/W and R_θJL = 30 °C/W, confirming suitability for surface-mount PCB layouts without forced cooling in most automotive and industrial environments.

Key Specifications

Pinout & Package

Package: SMA (DO-214AC), surface-mount, low-profile case with matte tin-plated leads solderable per J-STD-002. Cathode indicated by band; polarity-critical for unidirectional operation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SMAJ18AHE3_A/I, the SMAJ18A-E3/61 offers identical protection performance without AEC-Q101 validation, while SMAJ18AHM3_A/I delivers equivalent reliability with halogen-free construction - both require no PCB redesign but differ in certification scope and material compliance.

Availability

SMAJ18AHE3_A/I is available at Aetrix Electronics and suitable for automotive power rail protection, industrial sensor interface hardening, and telecom DC feed surge suppression requiring stable component supply, full traceability, and long-term lifecycle support.

Supply support for SMAJ18AHE3_A/I 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

Vishay General Semiconductor is a global leader in discrete semiconductors, specializing in diodes, rectifiers, TVS devices, and optoelectronics with emphasis on reliability, efficiency, and application-specific optimization.

The SMAJ series was engineered for high-energy transient suppression in harsh environments - targeting automotive, industrial, and telecom systems where robustness, fast response, and AEC-Q101 validation are mandatory.

FAQ

What is the clamping voltage of the SMAJ18AHE3_A/I under maximum rated surge current?

The SMAJ18AHE3_A/I has a maximum clamping voltage (V_C) of 29.2 V at its rated peak pulse current (I_PPM) of 13.7 A, measured using the standardized 10/1000 μs waveform. This value is guaranteed across the full operating temperature range and confirms the device's ability to limit transient overvoltage to a safe level for 24 V system components. The SMAJ18AHE3_A/I datasheet specifies this parameter in Table 1 under ELECTRICAL CHARACTERISTICS.

Is the SMAJ18AHE3_A/I suitable for automotive applications?

Yes, the SMAJ18AHE3_A/I is AEC-Q101 qualified, making it suitable for automotive applications including engine control units, body electronics, and ADAS modules. Its qualification covers temperature cycling, high-temperature reverse bias, and surge endurance testing. The SMAJ18AHE3_A/I also meets UL 497B for surge protector classification and is rated for operation from -55 °C to +150 °C, supporting under-hood and cabin environments.

What does the "HE3" suffix indicate in SMAJ18AHE3_A/I?

The "HE3" suffix in SMAJ18AHE3_A/I denotes a RoHS-compliant, AEC-Q101 qualified version with standard matte tin plating. The "H" indicates the packaging option (7" or 13" tape-and-reel), "E3" confirms RoHS compliance, and the "A/I" denotes the reel size variant (I = 13" reel, 7500 pcs). This distinguishes it from commercial-grade variants like SMAJ18A-E3/61 and halogen-free versions like SMAJ18AHM3_A/I.

How does the SMAJ18AHE3_A/I compare to bidirectional TVS diodes like SMAJ18CA?

The SMAJ18AHE3_A/I is unidirectional and intended for DC line protection where polarity is fixed (e.g., VBUS or 24 V supply), offering lower leakage and optimized forward conduction. In contrast, SMAJ18CA is bidirectional and suited for AC or floating signal lines. The SMAJ18AHE3_A/I cannot replace SMAJ18CA in symmetrical surge scenarios without circuit redesign, as its cathode band enforces polarity-dependent operation.

What is the thermal resistance of the SMAJ18AHE3_A/I, and how does it affect PCB layout?

The SMAJ18AHE3_A/I has a typical junction-to-ambient thermal resistance (R_θJA) of 120 °C/W and junction-to-lead resistance (R_θJL) of 30 °C/W, measured on 0.2" × 0.2" copper pads. This means adequate copper area must be provided at both terminals to maintain safe junction temperatures during repetitive surges. For high-duty-cycle applications, adding thermal vias or larger copper pours is recommended - the SMAJ18AHE3_A/I's thermal specs assume baseline pad layout per Vishay's DO-214AC footprint guidelines.