PCB Layout and Failure Considerations for TVS Diodes

Rod Macpherson

When using transient voltage suppressor (TVS) diodes for surge protection, particular care must be taken with PCB layout—especially the tracking between supply rails and the TVS device. For example, in systems with a 12 V rail and a separate 0 V reference (not chassis ground), a TVS diode may be placed between 12 V and 0 V to clamp surge events. In such cases, the routing to the TVS must not be implemented as a spur branching off the main power tracks.

Spur connections can be vulnerable during high-energy surge events. In practice, these narrow or elongated tracks may fail open-circuit due to excessive current or thermal stress, effectively disconnecting the TVS diode from the circuit. This failure can be difficult to detect during normal operation, leaving the system unprotected without any obvious indication.

The primary and most common failure mode of a TVS diode is a short circuit. In many safety-related applications, this is a desirable and predictable outcome. A shorted TVS typically results in a detectable fault condition, allowing the system to shut down safely and prompt maintenance or repair. By contrast, an open-circuit failure is far more problematic, as it provides no indication that surge protection has been lost. If the circuit lacks adequate current limiting or fuse protection, extreme surge conditions may even cause the TVS device to catastrophically fail or vaporize entirely.