Vishay General Semiconductor - Diodes Division SMAJ18AHM3_A/H

Overview

SMAJ18AHM3_A/H 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 stand-off voltage (VWM), 20.0–22.1 V breakdown voltage (VBR) at 10 mA test current, 29.2 V maximum clamping voltage (VC) at 13.7 A peak pulse current (IPPM), and 400 W peak pulse power rating with 10/1000 μs waveform - deployed on power rails and signal lines in automotive ECUs and industrial sensor interfaces.

For engineers reviewing the SMAJ18AHM3_A/H datasheet, SMAJ18AHM3_A/H pinout, SMAJ18AHM3_A/H application, or SMAJ18AHM3_A/H equivalent, key selection criteria include clamping performance under 13.7 A surge, thermal resistance (RθJA = 120 °C/W), AEC-Q101 qualification status, unidirectional polarity marking, and compatibility with automated SMT placement on 5.0 mm × 5.0 mm copper pads.

Technical Context

This TVS diode operates as a voltage-clamped shunt protector: when reverse voltage exceeds VBR (20.0–22.1 V), it avalanches to limit transient energy by diverting surge current to ground. Its glass-passivated junction ensures stable breakdown and low leakage (<1.0 μA at VWM).

Designed for single-polarity DC circuits, SMAJ18AHM3_A/H uses cathode-band polarity identification and delivers 400 W peak pulse power only up to 78 V; above that threshold, derated to 300 W per Fig. 2. It meets MSL Level 1 (260 °C reflow) and supports repetitive surge duty cycle ≤0.01 %.

Key Specifications

Pinout & Package

Package: SMA (DO-214AC), surface-mount, low-profile case with matte tin-plated leads solderable per J-STD-002. Cathode identified by black band; anode is unmarked end.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SMAJ18AHM3_A/H, SMAJ18AHE3_A/H offers identical protection performance without halogen-free compliance or AEC-Q101 validation, while SMBJ18A-HM3 provides 50 % higher pulse power in a physically larger package - requiring layout revision but enabling more demanding surge environments.

Availability

SMAJ18AHM3_A/H is available at Aetrix Electronics and suitable for automotive electronic control units, industrial sensor interfaces, and telecom power supply inputs requiring stable component supply, AEC-Q101 assurance, and halogen-free compliance.

Supply support for SMAJ18AHM3_A/H 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 designs and manufactures discrete semiconductors including diodes, MOSFETs, and TVS devices, with emphasis on high-reliability, automotive-qualified components.

The SMAJ series targets cost-sensitive yet robust transient protection in automotive, industrial, and communications systems - optimized for automated SMT assembly and high-volume production with MSL Level 1 compatibility.

FAQ

What is the clamping voltage of SMAJ18AHM3_A/H at its rated peak pulse current?

The SMAJ18AHM3_A/H has a maximum clamping voltage (VC) of 29.2 V at its specified peak pulse current (IPPM) of 13.7 A, measured using the standardized 10/1000 μs double-exponential waveform. This value defines the upper voltage limit imposed on protected circuitry during surge events and is confirmed in the Electrical Characteristics table on page 2 of Vishay document 88390. The SMAJ18AHM3_A/H maintains this clamping performance across its full operating temperature range (−55 °C to +150 °C).

Is SMAJ18AHM3_A/H qualified for automotive applications?

Yes, SMAJ18AHM3_A/H is AEC-Q101 qualified, as indicated by the "HM3" suffix and confirmed in the Ordering Information section (page 3) and Notes (page 2) of Vishay document 88390. This qualification covers stress tests including high-temperature reverse bias, temperature cycling, and ESD, making SMAJ18AHM3_A/H suitable for under-hood and chassis-mounted automotive electronics where reliability under thermal and mechanical stress is mandatory.

What does the "HM3" suffix signify in SMAJ18AHM3_A/H?

The "HM3" suffix in SMAJ18AHM3_A/H denotes halogen-free, RoHS-compliant construction with AEC-Q101 qualification. Per Vishay's ordering documentation, HM3 parts use molding compounds free of brominated flame retardants and meet JEDEC JESD201 Class 2 whisker resistance requirements. This distinguishes SMAJ18AHM3_A/H from E3 (RoHS-only) and HE3 (AEC-Q101, non-halogen-free) variants - confirming its suitability for environmentally regulated automotive and industrial deployments.

How is polarity identified on SMAJ18AHM3_A/H?

SMAJ18AHM3_A/H uses a visible cathode band (black stripe) on the SMA (DO-214AC) package to identify the cathode terminal; the opposite end is the anode. As a unidirectional TVS, it conducts surge current only when the cathode is at higher potential than the anode - meaning it must be installed with the banded end toward the protected line and the anode toward ground. This polarity marking is defined in the Mechanical Data section and verified in the device's schematic symbol on page 1 of document 88390.

What is the thermal resistance of SMAJ18AHM3_A/H, and how does it affect layout?

SMAJ18AHM3_A/H has a typical junction-to-ambient thermal resistance (RθJA) of 120 °C/W when mounted on the minimum recommended 0.2" × 0.2" (5.0 mm × 5.0 mm) copper pads per terminal, as specified in the Maximum Ratings table. This value directly impacts sustained power handling: at 3.3 W steady-state dissipation, junction temperature rise would reach ~400 °C - confirming that SMAJ18AHM3_A/H is intended for transient-only operation. Layout must replicate the specified pad dimensions to achieve rated surge performance and avoid thermal runaway during repetitive pulses.