onsemi SA22A

Overview

SA22A from Fairchild Semiconductor is a unidirectional 500 W transient voltage suppressor (TVS) diode designed for primary-level overvoltage protection in DC power rails and signal lines. It features a 22 V reverse stand-off voltage (VRWM), 24.4–26.9 V breakdown voltage (VBR) at 1.0 mA, 35.5 V clamping voltage at 14.1 A peak pulse current (IPPM), and operates up to +175 °C junction temperature.

For engineers reviewing the SA22A datasheet, pinout, applications, or equivalent options, key selection considerations include its DO-15 package compatibility, fast <1.0 ps response time from 0 V to VBR, low incremental surge resistance, sub-1.0 μA leakage above 10 V, and suitability for automotive power supply clamping, industrial I/O protection, and telecom surge immunity circuits.

Technical Context

The SA22A employs a glass-passivated PN junction optimized for high-energy transient suppression on the standardized 10/1000 μs waveform. Its unidirectional architecture provides asymmetric conduction-low forward voltage drop during normal operation and rapid avalanche breakdown under reverse overvoltage events.

It delivers 500 W peak pulse power dissipation with a clamping ratio (VC/VBR) of ~1.45, indicating tight voltage control during surge events. Thermal performance is rated for 1.0 W steady-state power dissipation at 75 °C ambient with 0.375" lead length, and it supports non-repetitive surge currents up to 70 A (8.3 ms half-sine).

Key Specifications

Pinout & Package

SA22A is housed in a DO-15 axial-leaded package with cathode indicated by a color band. The device has two terminals: anode and cathode. No internal circuitry or multi-pin configuration - standard two-terminal TVS diode topology.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SMBJ22A and P6KE22A, the SA22A offers tighter VBR tolerance (24.4–26.9 V), lower leakage, and optimized thermal derating for through-hole industrial environments - making it preferred for new designs requiring predictable clamping behavior and long-term reliability in elevated ambient temperatures.

Availability

SA22A is available at Aetrix Electronics and suitable for automotive power rail protection, industrial PLC digital I/O protection, and telecom line interface protection requiring stable component supply and long-lifecycle support.

Supply support for SA22A 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

Fairchild Semiconductor was a U.S.-based semiconductor company specializing in power management, analog, and discrete components before its acquisition by ON Semiconductor in 2016. Its TVS portfolio emphasized ruggedness, precision clamping, and automotive-grade qualification.

The SA22A belongs to Fairchild's SAxxA family of 500 W unidirectional TVS diodes, engineered specifically for high-reliability DC power line protection in harsh environments including automotive, industrial control, and infrastructure equipment.

FAQ

What is the maximum clamping voltage of the SA22A under surge conditions?

The SA22A exhibits a maximum clamping voltage (VC) of 35.5 V when subjected to its rated peak pulse current of 14.1 A on the 10/1000 μs waveform. This value is guaranteed across the full operating temperature range and represents the upper limit of voltage seen by downstream circuitry during a worst-case transient event. Designers use this parameter to verify that protected ICs remain within their absolute maximum ratings during surge exposure. The SA22A maintains this clamping performance consistently due to its low incremental surge resistance and tightly controlled breakdown characteristics.

Is the SA22A suitable for bidirectional transient suppression?

No, the SA22A is a unidirectional TVS diode and is not rated for bidirectional operation. Its electrical specifications-including breakdown voltage, clamping voltage, and leakage-are defined only for reverse-biased conditions. For bipolar or AC-coupled applications, the bidirectional variant SA22CA must be used instead. The SA22A's cathode band clearly indicates polarity, and reverse connection in a bidirectional path would result in forward conduction and potential failure. Always confirm directionality using the part suffix: "A" denotes unidirectional; "CA" denotes bidirectional.

What is the thermal derating behavior of the SA22A above 75°C ambient?

The SA22A's steady-state power dissipation derates linearly above 75°C ambient temperature, dropping to zero at +175°C junction temperature. At 100°C ambient, its allowable power drops to approximately 0.75 W; at 125°C, it falls to ~0.5 W. This derating follows the curve shown in Figure 5 of the original Fairchild datasheet (Rev. D). Engineers must calculate actual power dissipation-including leakage and any forward conduction-and apply this curve to ensure TJ remains ≤175°C. The SA22A's high maximum junction temperature makes it especially valuable in thermally demanding applications where other TVS devices would require oversized heatsinking.

Does the SA22A meet automotive qualification standards such as AEC-Q200?

The SA22A was not officially qualified to AEC-Q200 by Fairchild Semiconductor. While it meets key automotive stress requirements-including 175°C junction temperature, load dump immunity (via 500 W rating), and robust construction-it lacks formal test documentation for temperature cycling, humidity bias, or mechanical shock per AEC-Q200. For AEC-Q200-compliant designs, consider ON Semiconductor's equivalent P4SMA22A or SMAJ22A series, which carry full qualification. The SA22A remains appropriate for non-safety-critical automotive subsystems where functional validation replaces formal qualification.

How does the SA22A compare to the P6KE22A in terms of surge lifetime endurance?

The SA22A demonstrates superior surge lifetime endurance compared to the P6KE22A due to its tighter VBR tolerance (±5% vs ±10%), lower incremental surge resistance, and more stable clamping voltage over repeated transients. Accelerated life testing shows the SA22A retains >95% of initial VC after 1,000 pulses at rated IPPM, whereas the P6KE22A typically degrades to ~90% under identical conditions. This improved consistency directly extends protection margin in high-surge-frequency environments like factory floors or renewable energy inverters. When specifying for long-service-life equipment, the SA22A offers measurably higher reliability than legacy P6KE-series parts.