A Transient Voltage Suppressor (TVS) diode is a specialized Zener-like device engineered to absorb fast, high-energy voltage spikes — ESD strikes, inductive kickback, lightning-induced surges on long cables — and clamp them to a safe level before they reach sensitive silicon. Unlike a regular Zener, a TVS has a huge die area, low parasitic inductance, and a response time measured in picoseconds, making it the right tool when nanosecond-scale transients are the threat.

Three voltages define every TVS:

• V_RWM (Reverse Working Voltage): the steady-state DC voltage at which the TVS draws negligible current. Pick this at or above your rail.
• V_BR (Breakdown Voltage): where it starts conducting hard, typically 10-15% above V_RWM.
• V_C (Clamping Voltage): the actual voltage across the TVS at its rated peak pulse current. This is what your downstream IC sees during the strike — and it's always higher than V_BR.

Unidirectional TVS parts (one diode) protect DC rails where polarity is fixed. Bidirectional TVS parts (two back-to-back) protect AC lines or differential pairs like RS-485 and CAN bus.

Real-world example: protecting a USB data line. USB 2.0 D+/D- signals swing 0-3.3V but must survive ±8 kV contact ESD per IEC 61000-4-2. A part like the PESD5V0U1BA has V_RWM = 5V (above the signal but below logic damage threshold), clamps to ~9V during an 8 kV strike, and has only ~0.5 pF capacitance — critical, because anything more would smear the 480 Mbps edges. Place it right at the connector, with the ground pin tied directly to chassis ground via the shortest possible trace.

Rule of thumb — sizing peak pulse current: For ESD applications, the standard 8/20 µs surge test injects energy roughly equal to:

I_PP ≈ V_surge / Z_source

For a typical 8 kV ESD event with ~330 Ω source impedance: I_PP ≈ 24 A. Pick a TVS rated at least 2× that, because clamping voltage degrades and the part heats up near its limit. For lightning-induced surges on outdoor cabling (10/1000 µs waveform, much more energy), step up to a 600W+ part or stage protection with a gas discharge tube upstream and a TVS downstream.

Layout matters more than the part choice. A 10 nH of trace inductance, hit by a 1 A/ns ESD edge, develops 10V across itself — completely defeating a 5V clamp. Keep the loop from TVS to victim pin to ground tiny, and tie ground to a solid plane.