System-Level ESD Protection for External High-Speed Interfaces

Electrostatic Discharge in Exposed User Ports

External user-facing connectors—such as USB Type-C, DisplayPort, and Ethernet jacks—are constantly exposed to electrostatic discharge (ESD) from human contact and cable plugging events. A high-voltage ESD strike passing through signal pins can permanently destroy sensitive system-on-chip (SoC) input circuitry.

Protecting internal silicon requires fast-acting Transient Voltage Suppressor (TVS) diodes placed strategically along high-speed signal paths.

Placement and Selection Rules for TVS Diodes

1. Ultra-Low Parasitic Capacitance: For multi-gigabit data lines, TVS diodes must feature parasitic capacitance below 0.2 pF to 0.5 pF. High capacitance distorts high-frequency signal eye diagrams and ruins channel impedance.
2. Direct Flow-Through Layout: Place TVS diode arrays directly at the connector receptacle entrance before any series resistors or filtering components. Route high-speed traces directly through the TVS pad footprint to avoid stub traces that increase ESD clamping voltage.
3. Low-Inductance Ground Return: Ensure the TVS ground pad connects directly to chassis ground using multiple wide vias. Low parasitic ground inductance minimizes clamping voltage spikes during rapid ESD events.