Reviewing the Current Path Around a PCB ESD Protector

Adding a protection device to the schematic does not establish the protection performance of the assembled interface. The PCB determines how the transient reaches the protector and where the diverted current flows. Review those paths along with the normal signal requirements before releasing the connector region.

Trace the complete connection

TI’s ESD layout guide identifies parasitic inductance between the connector, protection device, return connection, and protected IC. Its examples show why physical routing matters in addition to the protector’s component specifications. Apply the selected device’s pinout and routing guidance rather than copying a different package’s arrangement. TI: ESD protection layout guide.

On the layout, follow each exposed signal from the connector to the protection device and onward to the circuit. Then trace the protector’s return path through pads, vias, planes, and any chassis connection specified by the design. Identify narrow sections, detours, layer transitions, and shared paths through sensitive circuitry.

Check placement and routing together

• Use the manufacturer’s recommended flow-through arrangement where appropriate.
• Avoid a long branch that leaves the protector electrically remote from the incoming route.
• Review the return connection with the actual board stackup.
• Keep protected and unprotected routing from coupling through an avoidable close parallel run.
• Check that the chosen protector’s capacitance and package geometry suit the interface.

For example, moving a protector closer to a connector may shorten the signal segment while leaving its return tied through a distant via. The review must include both changes. A short distance measured between component bodies is not a complete description of the current path.

Coordinate the enclosure and connector

Document any shield or chassis connections and the mechanical arrangement used during testing. A board tested on a bench without its normal cable and enclosure may not represent the final product. Keep isolation boundaries and grounding architecture under the responsible system designer’s control; do not add an arbitrary bridge merely to shorten a route.

Validate the product configuration

Use the applicable product test plan and qualified equipment to evaluate the assembled interface. Record the hardware revision, cables, enclosure, operating mode, test locations, and observed behavior. Component-level ratings do not automatically establish system-level immunity. If a failure occurs, retain the configuration and investigate the path before replacing the protector with a higher headline rating. The accepted layout should preserve both normal signal performance and the demonstrated transient behavior, with enough documentation to assess later connector or enclosure changes.

Include protector orientation and unused-pin treatment in the footprint check; a correct schematic cannot compensate for an incorrect package mapping.