Taiwan Semiconductor Corporation SMAJ170CAH

Overview

SMAJ170CAH from Taiwan Semiconductor is a bidirectional 400W transient voltage suppressor (TVS) diode in DO-214AC (SMA) package, designed for automotive-grade overvoltage protection with 170V working stand-off voltage, 189–209V breakdown range, and 304V clamping voltage at 1A peak pulse current under 10/1000μs waveform. It meets AEC-Q101 qualification and ISO 7637-2 Pulse 1/2a/2b/3a/3b for robust vehicle electrical system protection.

For engineers reviewing the SMAJ170CAH datasheet, SMAJ170CAH pinout, SMAJ170CAH application, or SMAJ170CAH equivalent, this device is selected for high-reliability DC bus protection in automotive power modules, on-board chargers, and industrial DC/DC converters where fast clamping (<1ps response), low leakage (<1μA @ 170V), and moisture-insensitive level-1 packaging are critical.

Technical Context

The SMAJ170CAH implements a glass-passivated silicon junction optimized for bidirectional transient suppression, with symmetrical breakdown behavior in both polarities per its CAH suffix designation. Its clamping performance is defined by a 10/1000μs standard surge waveform, delivering 304V max clamping at 1A IPPM while maintaining ≤1μA reverse leakage above 170V VWM.

Thermal derating follows Fig.2 in the datasheet: peak pulse power remains at 400W up to 25°C ambient but declines linearly to ~240W at 100°C. Junction temperature is rated from –55°C to +150°C, supporting operation in under-hood automotive environments without thermal runaway risk.

Key Specifications

Pinout & Package

DO-214AC (SMA) package: molded plastic case with cathode band marking; dual axial terminals suitable for automated placement; polarity indicated by single black band on cathode end.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SMAJ170CAH, SMAJ170AHE3/5BT offers tighter clamping but reduced pulse power headroom, while P6SMB170CA trades compactness for enhanced thermal robustness and lower VC-neither is pin-compatible due to differing package outlines (DO-214AC vs. DO-214AA).

Availability

SMAJ170CAH is available at Aetrix Electronics and suitable for automotive power modules, on-board DC/DC converters, and industrial motor drive systems requiring stable component supply with AEC-Q101 compliance and ISO 7637-2 transient immunity.

Supply support for SMAJ170CAH 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 analog and discrete semiconductor manufacturer headquartered in Hsinchu, Taiwan, specializing in TVS diodes, rectifiers, and power MOSFETs for automotive and industrial markets.

The SMAJ series was developed specifically for AEC-Q101-compliant transient suppression in harsh automotive environments, emphasizing fast response, low leakage, and robust surge endurance across wide temperature ranges.

FAQ

What does the 'CAH' suffix indicate in SMAJ170CAH?

The 'CAH' suffix in SMAJ170CAH denotes a bidirectional configuration with AEC-Q101 qualification. Unlike unidirectional 'H' variants, the CAH version provides symmetrical clamping in both polarities-enabling protection of floating or AC-coupled lines without polarity constraints. This matches the electrical characteristics specified for bidirectional use in the datasheet's "Devices for Bipolar Applications" section, where VBR, IR, and VC apply identically in forward and reverse directions.

Is SMAJ170CAH suitable for ISO 7637-2 Pulse 5a (load dump) protection?

No, SMAJ170CAH is not rated for ISO 7637-2 Pulse 5a, which specifies up to 120V superimposed on 14V nominal systems with 400ms duration. The SMAJ170CAH's 400W rating applies to 10/1000μs waveforms (Pulse 1/2a/2b/3a/3b), not long-duration load dump events. For Pulse 5a, a dedicated load dump suppressor such as a TVS with higher energy rating (e.g., 5.0SMDJ series) or active clamp circuit is required alongside SMAJ170CAH.

What is the maximum clamping voltage of SMAJ170CAH at its rated peak pulse current?

The maximum clamping voltage of SMAJ170CAH is 304 V at 1 A peak impulse current (IPPM) under the standardized 10/1000μs waveform. This value is measured per Figure 5 in the datasheet and represents the worst-case voltage imposed on protected circuitry during a full-rated transient event. It is derived from the device's intrinsic avalanche characteristics and junction design, not extrapolated or estimated.

Does SMAJ170CAH require derating at elevated ambient temperatures?

Yes, SMAJ170CAH requires thermal derating above 25°C ambient temperature. Per Figure 2 in the datasheet, its peak pulse power decreases linearly from 400W at 25°C to approximately 240W at 100°C. This derating is mandatory for reliable operation in under-hood automotive applications and must be factored into system-level surge margin calculations using the published derating curve.

How does the DO-214AC (SMA) package of SMAJ170CAH compare to DO-214AA (SMB) in thermal performance?

The DO-214AC (SMA) package of SMAJ170CAH has lower thermal mass and smaller pad area than DO-214AA (SMB), resulting in higher junction-to-ambient thermal resistance. While both packages support the same 400W peak pulse rating under ideal conditions, the SMA variant reaches higher steady-state temperatures during repetitive surges. Layout best practices-such as maximizing copper pour on both terminals and using thermal vias-must be applied to maintain TJ ≤150°C in high-duty-cycle applications.