TVS Protection & PCB Layout Best Practices
The best ESD test result comes from a design that never lets the transient reach a sensitive pin in the first place: the right TVS diode, placed and routed correctly, stops most of the current before it ever gets close.
A TVS (transient voltage suppressor) diode must satisfy two conditions simultaneously: its working voltage (VRWM) must sit above your signal's normal operating range so it stays off during normal operation, and its clamp voltage (VC) at the expected ESD current must sit below the maximum voltage rating of the IC it protects.
| Rule | Why it matters |
|---|---|
| Place TVS as close as possible to the connector/entry point | Minimizes the trace length carrying the raw transient before it is clamped |
| Route TVS ground return with a short, low-inductance path to chassis/earth | A long or high-inductance ground path lets voltage build across it during the fast current pulse, reducing effective clamping |
| Keep sensitive signal traces away from connector edges and seams | Reduces direct or capacitively-coupled exposure to an air-discharge event near the enclosure opening |
| Use a continuous ground plane under high-speed and I/O traces | Provides a low-impedance return path and reduces loop area for coupled transients |
| Add a moat or slot only with a deliberate single-point stitching strategy | An unintentional ground-plane split can force return current through a much longer, higher-impedance path |
Star-point chassis ground. Chassis grounded to PCB ground at a single, low-impedance connection near the connector entry -- ESD current stays on the enclosure instead of crossing the signal ground plane.
Bridge every seam. Conductive gaskets or spring fingers keep the enclosure electrically continuous, so an air discharge at a seam spreads along the shield instead of finding a high-impedance path inside.
Choke the cables. Ferrite beads or common-mode chokes at the cable entry add high-frequency impedance in the ESD current's path without disturbing the intended low-frequency signal.
Two-stage clamp at exposed I/O. A TVS at the connector takes the bulk current; a small series resistor (or ESD-rated connector) after it drops the residual before the IC pin.
Every protection-part selection is the same seven questions asked in the same order. Work through them once for each externally exposed interface on your product, and the datasheet parameters you need fall out automatically.
Module 8 Quiz
Select the best answer for each question. Instant feedback is provided after each response.