onsemi SA18CA

Overview

SA18CA from Fairchild Semiconductor is a bidirectional 500 W transient voltage suppressor (TVS) diode in DO-15 package, with 18 V reverse stand-off voltage (VRWM), 20.0–22.1 V breakdown voltage (VBR), and 29.2 V clamping voltage (VC) at 17.2 A peak pulse current on 10/1000 μs waveform-designed for surge protection in DC power lines and I/O interfaces.

For engineers reviewing the SA18CA datasheet, pinout, applications, or equivalent options, this device delivers fast sub-5 ns response time, low incremental surge resistance, glass-passivated junction reliability, and bidirectional clamping capability suitable for ESD and lightning-induced transients in industrial control and telecom front-end circuits.

Technical Context

The SA18CA operates as a bipolar junction TVS diode with symmetrical clamping behavior in both directions, enabling robust protection without polarity constraints. Its breakdown occurs at 20.0–22.1 V (IT = 1.0 mA), and it maintains ≤1 μA reverse leakage above 10 V at VRWM = 18 V.

It sustains 500 W peak pulse power on standardized 10/1000 μs waveform, with thermal derating to 1.0 W steady-state dissipation at 75°C ambient (0.375" lead length). Junction temperature rating is +175°C, supporting operation in harsh environments.

Key Specifications

Pinout & Package

SA18CA is housed in a DO-15 axial-leaded package with no cathode band-consistent with bidirectional construction. Leads are tinned and designed for through-hole mounting with 0.375" lead length standard for thermal rating.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SA18CA, SMBJ18CA offers higher surge capacity and SMT compatibility, while P6SMB18CA provides tighter breakdown tolerance in the same footprint-both require layout changes but deliver measurable improvements in manufacturability or parametric consistency.

Availability

SA18CA is available at Aetrix Electronics and suitable for industrial automation, telecom infrastructure, and automotive body electronics requiring stable component supply and long-lifecycle support.

Supply support for SA18CA 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 legacy TVS portfolio remains widely deployed and supported.

The SAxxCA series was engineered specifically for high-reliability unidirectional and bidirectional surge suppression in industrial and transportation systems-emphasizing ruggedness, repeatable clamping, and thermal resilience.

FAQ

What is the clamping voltage of SA18CA at its rated peak pulse current?

The SA18CA exhibits a maximum clamping voltage (VC) of 29.2 V when subjected to its rated peak pulse current of 17.2 A on the standard 10/1000 μs waveform. This value is measured under controlled lab conditions per JEDEC standards and defines the upper voltage limit imposed on protected circuitry during surge events. Designers use this parameter to verify that downstream components remain within their absolute maximum ratings during transient exposure. The SA18CA consistently achieves this performance across its qualified temperature range.

Is SA18CA unidirectional or bidirectional, and how can I identify its polarity?

SA18CA is a bidirectional transient voltage suppressor, indicated by the "CA" suffix per Fairchild's naming convention. Unlike unidirectional variants (e.g., SA18A), it has no cathode band on the DO-15 package-both leads are electrically identical and symmetric. This allows installation without regard to orientation, simplifying assembly and eliminating risk of reverse placement. Its electrical characteristics-including breakdown and clamping-are specified identically in both directions, making it ideal for AC-coupled or polarity-agnostic protection points.

What is the maximum steady-state power dissipation for SA18CA?

The SA18CA is rated for 1.0 W steady-state power dissipation at an ambient temperature of 75°C with 0.375" lead length, per JEDEC test conditions. This rating decreases linearly above 75°C, reaching zero at 175°C junction temperature. Engineers must apply this derating curve when calculating safe continuous power handling in thermally constrained enclosures. The 1.0 W limit reflects thermal conduction through leads-not package surface area-so PCB copper pour has minimal effect unless leads are soldered to wide thermal pads.

Does SA18CA meet any international surge immunity standards?

Yes, the SA18CA's 500 W peak pulse power rating on the 10/1000 μs waveform aligns with the energy levels defined in IEC 61000-4-5 for surge immunity testing at Level 4 (4 kV line-to-earth, 2 kV line-to-line). Its sub-5 ns response time and low clamping voltage further support compliance in end-equipment standards such as EN 55032 and UL 62368-1. While the device itself is not certified, its parameters enable system-level pass/fail results when applied per recommended layout guidelines in Fairchild's application notes.

How does SA18CA compare to SA18A in terms of electrical behavior?

The SA18CA is bidirectional with symmetrical clamping in both directions, whereas SA18A is unidirectional and conducts only in reverse bias-requiring correct cathode orientation. SA18CA has identical VRWM (18 V) and VBR (20.0–22.1 V), but its IR is specified ≤1 μA above 10 V in both polarities, while SA18A exhibits typical IR <1 μA only in reverse. Clamping voltage is nearly identical (29.2 V vs. 29.0 V), but SA18CA's bidirectional nature eliminates polarity-dependent failure modes in AC or floating systems-making SA18CA the preferred choice for robust, layout-insensitive protection.