onsemi SA170CA

Overview

SA170CA from Fairchild Semiconductor is a 500 W bidirectional transient voltage suppressor (TVS) diode in DO-15 package, with 170 V reverse stand-off voltage (VRWM), 189–209 V breakdown voltage (VBR), and 275 V clamping voltage (VC) at peak pulse current. It delivers fast response (<5.0 ns), low leakage (<1.0 µA at VRWM), and operates up to +175°C junction temperature - used for surge protection in AC power inputs and telecom line interfaces.

For engineers reviewing the SA170CA datasheet, pinout, applications, or equivalent options, key selection criteria include clamping voltage margin vs. protected IC's absolute maximum rating, bidirectional polarity for AC-coupled lines, DO-15 thermal derating above 75°C ambient, and IFSM surge capability for lightning-induced transients.

Technical Context

The SA170CA is a glass-passivated, bidirectional TVS diode designed to shunt high-energy transients (e.g., IEC 61000-4-5 Level 4) away from sensitive downstream circuitry. Its symmetrical avalanche structure enables identical clamping behavior in both directions, eliminating need for polarity-aware placement on AC or differential signal paths.

It operates under 10/1000 µs standard surge waveform, with 500 W peak pulse power rating and 70 A non-repetitive forward surge current (IFSM). Junction temperature reaches +175°C, supporting use in high-ambient industrial environments without active cooling.

Key Specifications

Pinout & Package

SA170CA uses the industry-standard DO-15 axial-leaded package with no cathode band (bidirectional construction). Leads are tinned and suitable for wave or hand soldering; thermal resistance from junction-to-ambient is 125°C/W with 0.375" lead length at TA = 75°C.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SMAJ170CA and SMA6J170A, SA170CA offers native bidirectional operation in DO-15 with verified 1.0 µA leakage - simplifying layout for AC-coupled interfaces and reducing BOM count versus dual-unidirectional solutions.

Availability

SA170CA is available at Aetrix Electronics and suitable for AC power input protection, telecom line interface, industrial motor drive control, and smart meter front-end applications requiring stable component supply and long-lifecycle support.

Supply support for SA170CA 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 analog and power semiconductor manufacturer, acquired by ON Semiconductor in 2016; its legacy TVS portfolio remains widely deployed in industrial and infrastructure designs.

The SAxxxC(A) series was engineered specifically for high-energy transient suppression in mains-connected equipment, emphasizing robustness, repeatable clamping, and DO-15 compatibility with legacy board layouts.

FAQ

What is the clamping voltage of SA170CA and how does it protect downstream components?

The SA170CA has a maximum clamping voltage (VC) of 275 V at its rated peak pulse current. This means that during a 10/1000 µs surge event, the voltage across the SA170CA will not exceed 275 V - limiting the stress imposed on downstream rectifiers, controllers, or isolation components. Because SA170CA is bidirectional, this clamping occurs equally for positive and negative transients, making it ideal for AC line protection where polarity is undefined.

Is SA170CA unidirectional or bidirectional, and how can I identify its polarity?

SA170CA is a bidirectional TVS diode, indicated by the "CA" suffix per Fairchild's naming convention. Unlike unidirectional variants (e.g., SA170A), it has no cathode band and both leads are electrically identical - enabling placement without regard to orientation. This eliminates risk of incorrect installation in AC or differential signal paths and simplifies PCB layout.

What is the maximum operating temperature for SA170CA, and how does thermal derating affect its power handling?

The SA170CA supports an operating junction temperature up to +175°C. Its steady-state power dissipation is rated at 1.0 W with 0.375" lead length at TA = 75°C, and derates linearly to zero at +175°C. For reliable long-term operation in enclosed industrial enclosures, designers must verify ambient temperature and airflow to ensure junction temperature stays within spec - especially under repeated surge conditions.

Can SA170CA be used in place of SA170A, and what are the functional trade-offs?

No - SA170CA and SA170A are not interchangeable. SA170A is unidirectional and requires correct anode/cathode orientation; SA170CA is bidirectional with symmetrical characteristics. Substituting SA170A for SA170CA on an AC line risks open-circuit failure during negative transients. Always match the "C" suffix for bidirectional use and confirm layout compatibility before replacement.

Does SA170CA meet IEC 61000-4-5 surge immunity requirements, and what test level does it support?

Yes - the SA170CA's 500 W peak pulse power rating corresponds to the 4 kV/2 Ω combination wave defined in IEC 61000-4-5 Ed. 3. When correctly applied with appropriate PCB trace inductance and grounding, SA170CA enables compliant protection for AC mains inputs and telecom interfaces. System-level validation is still required, but SA170CA provides the foundational clamping performance needed to pass Level 4 testing.