Taiwan Semiconductor Corporation SMAJ170A

Overview

SMAJ170A from Taiwan Semiconductor is a unidirectional surface-mount transient voltage suppressor (TVS) diode in DO-214AC (SMA) package, designed for robust overvoltage protection in DC power rails. It features a 170 V working stand-off voltage (VWM), 189–209 V breakdown voltage (VBR) at 1 mA test current, and clamps to ≤275 V at 1.1 A peak impulse current under 10/1000 µs waveform - delivering 400 W peak pulse power capability up to 78 V and 300 W above.

For engineers reviewing the SMAJ170A datasheet, SMAJ170A pinout, SMAJ170A application, or SMAJ170A equivalent, this device is selected for high-reliability surge suppression in automotive power modules, industrial DC/DC converters, and lighting drivers where fast response (<1 ps), low leakage (<1.1 µA at 170 V), and ISO 7637-2 Pulse 1/2a/2b/3a/3b compliance are required.

Technical Context

The SMAJ170A operates as a unidirectional avalanche diode with glass-passivated junction, enabling sub-nanosecond response to transients and stable clamping performance across -55°C to +150°C junction temperature range. Its single-die DO-214AC construction supports automated placement and meets JESD201 Class 2 whisker resistance and UL 94V-0 flammability standards.

Electrical behavior is defined by strict VBR min/max limits (189–209 V), guaranteed clamping voltage (VC ≤ 275 V at IPPM = 1.1 A), and low IR (<1.1 µA @ VWM = 170 V). It sustains 40 A non-repetitive forward surge (IFSM) and derates linearly above 25°C ambient per published curve (Fig.2).

Key Specifications

Pinout & Package

Package: DO-214AC (SMA), surface-mount, single-diode unidirectional configuration with cathode band marking. Matte tin-plated leads comply with J-STD-002 solderability and JESD201 Class 2 whisker resistance.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SMAJ170A, Littelfuse and ON Semiconductor versions offer identical clamping performance and mechanical fit but differ slightly in leakage tolerance and VBR binning - enabling optimized selection for cost, availability, or ultra-low-I_R requirements without PCB or schematic modification.

Availability

SMAJ170A is available at Aetrix Electronics and suitable for automotive power modules, industrial DC/DC converters, and LED driver designs requiring stable component supply with full traceability and long-term lifecycle support.

Supply support for SMAJ170A 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, and rectifiers for industrial, automotive, and consumer applications.

The SMAJ series was developed specifically for high-energy transient suppression in harsh environments, emphasizing fast response, repeatable clamping, and AEC-Q101 readiness for under-hood and rail-mounted deployments.

FAQ

What is the maximum clamping voltage of SMAJ170A under standard 10/1000 µs surge conditions?

The SMAJ170A has a maximum clamping voltage (VC) of 275 V when subjected to its rated peak impulse current of 1.1 A using the 10/1000 µs waveform. This value is measured per JEDEC-standard test conditions and guarantees protection for downstream components rated up to 300 V, making SMAJ170A suitable for 24 V and 48 V industrial bus protection where voltage overshoot must be tightly bounded.

Is SMAJ170A unidirectional or bidirectional, and how is polarity identified?

SMAJ170A is a unidirectional TVS diode, meaning it conducts only in reverse bias during overvoltage events. Polarity is marked by a cathode band on the DO-214AC package body - the banded end connects to the protected line (e.g., 170 V rail), while the anode connects to ground. This configuration ensures no forward conduction during normal operation, preserving system efficiency and preventing unintended current paths.

Does SMAJ170A meet automotive surge immunity standards such as ISO 7637-2?

Yes, SMAJ170A is explicitly rated to meet ISO 7637-2 Pulse 1, 2a, 2b, 3a, and 3b waveforms. Its 300 W peak pulse power rating above 78 V, fast <1 ps response, and controlled clamping behavior enable direct implementation in automotive power nets without additional filtering - supporting compliance for ECU, body control module, and ADAS power supply designs.

What is the junction temperature range and thermal derating behavior of SMAJ170A?

SMAJ170A operates across a junction temperature range of -55°C to +150°C and follows a linear derating curve above 25°C ambient, as shown in Figure 2 of the official datasheet. At 100°C ambient, its peak pulse power drops to approximately 220 W - a critical consideration for enclosed automotive or industrial enclosures where thermal management affects sustained surge handling capability.

How does SMAJ170A compare to SMAJ170 in terms of breakdown voltage and leakage current?

SMAJ170A offers tighter VBR tolerance (189–209 V) versus SMAJ170 (189–231 V) and slightly higher maximum IR (1.1 µA vs. 1.0 µA at VWM = 170 V). The "A" suffix denotes improved parameter consistency - beneficial for designs requiring precise clamping thresholds and predictable leakage in battery-critical or high-reliability applications where marginal VBR spread could affect system-level fault detection.