Bottom line
Pick stand-off voltage above the highest normal voltage, clamping voltage below what the protected circuit survives, and pulse capability matched to the ISO pulse your OEM requires. Then check line capacitance for anything carrying data.
Three voltages that decide everything
| Parameter | How to choose | Common error |
|---|---|---|
| VRWM stand-off | Above the highest normal voltage, including jump start | Using the nominal 12 V or 24 V figure |
| VBR breakdown | Between stand-off and the clamping requirement | Ignoring the tolerance band |
| VC clamping | Below the absolute maximum of the protected pin | Comparing clamping at a current the pulse never reaches |
Match the pulse, not the marketing number
Automotive transients are defined by ISO 7637-2 (conducted pulses on the supply) and ISO 10605 (electrostatic discharge). A generic “600 W” peak-power rating says little unless it is quoted for the pulse shape and duration you must survive.
- Pulse 1: negative transient from inductive loads being switched off.
- Pulse 2a: positive spike from switching off a parallel load.
- Pulse 3a/3b: fast switching bursts, the reason low-capacitance parts exist on data lines.
- Pulse 5: load dump — the highest energy event, usually handled upstream by a larger TVS.
Where the parts go
- One TVS at the board input, sized for load dump energy.
- One protection device per external connector — a single board-level TVS cannot clamp a connector several centimetres away.
- Low-capacitance arrays directly at the transceiver pins for CAN, LIN, USB and automotive Ethernet.
- Keep the return path short: protection effectiveness is dominated by layout, not by the device's headline rating.
Related products
| Part number | Brand | Package | Qualification | Operating temperature | Key parameters | Docs | Actions |
|---|---|---|---|---|---|---|---|
| 1SMB30CAT3G In stock | onsemi | SMB | AEC-Q101 qualified | -55 °C ~ +150 °C | vrwm: 30 V · ppp: 600 W · direction: Uni-directional | Datasheet ↗ | |
| 1.5KE24CA-TP | MCC | — | Qualification to be verified | To be confirmed | To be confirmed | Datasheet ↗ | |
| 1.5KE250A-TP In stock | MCC | DO-201AE | Qualification to be verified | To be confirmed | To be confirmed | Datasheet ↗ | |
| 1.5KE480A | WAYON | — | Qualification to be verified | To be confirmed | To be confirmed | Datasheet ↗ | |
| 1.5SMC33CA | LITTLEFUSE | — | Qualification to be verified | To be confirmed | To be confirmed | Datasheet ↗ | |
| 1.5SMC6.8CA In stock | Littelfuse | SMC | Qualification to be verified | To be confirmed | To be confirmed | To be confirmed |
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FAQ
Uni-directional or bi-directional?
DC power lines normally use uni-directional devices (they clamp only above the rail); signal lines that swing both ways, and AC-coupled lines, use bi-directional parts.
Can I replace a TVS with a Zener?
No. Zeners are not characterised for high-energy transient absorption and are not qualified for the pulse waveforms.
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Source：ISO 7637-2 and ISO 10605 test definitions; manufacturer TVS datasheets.
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