Protection against ESD

Electrostatic discharge (ESD) is a sudden flow of charge between two bodies at different potentials, caused by contact or by an electric field. It can reach several kV with nanosecond rise time and damage ICs (gate-oxide breakdown, junction burn-out). Protection is applied at three levels: prevention at the source, shielding/diversion, and circuit protection.

Prevent charge build-up

• Use anti-static mats, wrist straps and grounded work tables during handling and assembly.
• Keep humidity at 40-60 percent; use anti-static packaging (conductive bags, foam).
• Avoid synthetic clothing and carpets near sensitive equipment; use ionisers.

Divert the discharge

• Put the circuit in a grounded metal enclosure so the discharge flows to ground, not through the electronics.
• Keep gaps and seams small; connect connector shells to chassis ground, not to signal ground.
• Use a guard ring/ground plane around I/O connectors and keep traces short.

Protect the circuit

• Add TVS diodes (transient voltage suppressors) or zener diodes at every external input/output to clamp the voltage.
• Use series resistors with a shunt capacitor (RC filter) or a ferrite bead to slow the pulse.
• Use varistors (MOV) or gas discharge tubes for larger surges.
• Use opto-isolators or transformers where galvanic isolation is needed.

 Connector pin --[R]--+--> to IC input
                      |
                  TVS / diode
                      |
                    GND (chassis)

The TVS conducts only when the voltage exceeds its breakdown value, sending the energy to ground.