onsemi SA17A

Overview

SA17A from Fairchild Semiconductor is a unidirectional 500 W transient voltage suppressor (TVS) diode designed for primary-level overvoltage protection in DC power lines and signal interfaces. It features a 17 V reverse stand-off voltage (VRWM), 18.9–20.9 V breakdown voltage (VBR) at 1.0 mA, 27.6 V clamping voltage at peak pulse current, and operates up to +175 °C junction temperature. It is used in industrial power supplies and automotive body control modules to suppress ESD and lightning-induced surges.

For engineers reviewing the SA17A datasheet, pinout, applications, or equivalent options, this page delivers verified electrical parameters, DO-15 package details, bidirectional variant context (SA17CA), clamping performance under 10/1000 μs waveform, and real-world selection guidance against comparable TVS diodes.

Technical Context

The SA17A employs a glass-passivated PN junction optimized for fast transient response (<1.0 ps rise time from 0 V to VBR) and low incremental surge resistance. Its unidirectional configuration provides asymmetric conduction: low-leakage blocking above VRWM and sharp avalanche clamping during overvoltage events.

Rated for 500 W peak pulse power on the standard 10/1000 μs waveform, it sustains 70 A non-repetitive forward surge current (IFSM) per JEDEC method and exhibits <1.0 μA reverse leakage at VRWM ≥10 V - confirmed at 17 V operating point.

Key Specifications

Pinout & Package

SA17A 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 multi-pin structure - simple two-terminal construction for series connection across protected lines.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SA17A, SMBJ17A offers higher surge power and SMT compatibility but requires PCB redesign, while P6KE18A matches form factor and improves clamping slightly at the cost of doubled leakage - both serve as functional alternatives when VRWM and DO-15 constraints align.

Availability

SA17A is available at Aetrix Electronics and suitable for industrial power input protection, automotive body control modules, telecom line interfaces, and renewable energy charge controllers requiring stable component supply and long-lifecycle support.

Supply support for SA17A 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 designer of high-performance analog and power semiconductors, acquired by ON Semiconductor in 2016; its legacy TVS portfolio remains widely deployed and supported.

The SAxxA series was engineered specifically for cost-effective, high-reliability transient suppression in DC-fed systems where DO-15 through-hole mounting, 500 W surge capacity, and tight VBR tolerance are critical.

FAQ

What is the clamping voltage of SA17A at its rated peak pulse current?

The SA17A clamps to 27.6 V at its peak pulse current of 18.1 A under the standard 10/1000 μs waveform. This value is measured per JEDEC test conditions and defines the maximum voltage imposed on protected circuitry during a full-rated surge event. Designers use this parameter to verify downstream components remain within absolute maximum ratings. The SA17A achieves this clamping performance while maintaining low incremental resistance and sub-nanosecond response.

Is SA17A unidirectional or bidirectional, and how does that affect circuit placement?

SA17A is a unidirectional TVS diode, meaning it conducts only during reverse-biased overvoltage events - i.e., when cathode voltage exceeds anode voltage by more than VBR. It must be placed with cathode toward the higher-potential rail (e.g., VBUS or VCC) and anode toward ground or lower potential. Unlike bidirectional variants such as SA17CA, SA17A does not protect against positive transients on grounded lines or negative transients on VCC, so topology must match its polarity-specific behavior.

What is the maximum operating junction temperature for SA17A, and how does it impact thermal design?

The SA17A has a maximum operating junction temperature of +175 °C, enabling use in high-ambient environments like engine compartments or enclosed industrial enclosures. However, its steady-state power dissipation is limited to 1.0 W at 75 °C ambient with 0.375" lead length. Thermal design must ensure junction temperature stays below 175 °C during both continuous leakage and transient events - often requiring board-level copper pour or airflow, especially in sealed housings where ambient may exceed 75 °C.

How does the SA17A compare to SA17CA in terms of electrical performance and application scope?

SA17A and SA17CA share identical VRWM (17 V), VBR (18.9–20.9 V), and VC (27.6 V) specifications, but SA17CA is bidirectional - providing symmetrical clamping for AC-coupled or floating lines like data buses or transformer secondaries. SA17A is restricted to DC rail protection with defined polarity. Neither is pin-compatible with the other due to internal structure differences, though both use DO-15 packaging. System-level choice depends on whether transient threats occur in both polarities.

Can SA17A be used in place of a Zener diode for overvoltage protection?

While SA17A shares avalanche breakdown behavior with Zener diodes, it is optimized for transient suppression - not regulation. Its 500 W peak pulse rating, low dynamic impedance, and sub-nanosecond response make it unsuitable as a precision voltage reference. Using SA17A as a Zener risks excessive power dissipation during sustained overvoltage and inaccurate regulation due to wide VBR tolerance (±1.0 V). For regulation, discrete Zeners or dedicated voltage references remain appropriate; SA17A should be reserved for surge clamping only.