ESD protection
/ E-S-D /
Shuffle across a carpet on a dry day and touch a doorknob, and snap, there is a spark and a sting. That spark can be several thousand volts, and while it barely tickles you, the same jolt fired into a chip's delicate gate can punch a hole straight through it in an instant. Electrostatic discharge, ESD, is that sudden dump of static charge, and ESD protection is everything we do to keep it from killing or quietly weakening sensitive components.
The danger is the voltage. A human body easily charges to between 2,000 and 15,000 volts, while a MOSFET gate insulator only a few nanometres thick breaks down at a few tens of volts. The discharge is fast (nanoseconds) and carries little energy, but it is more than enough to rupture a gate or melt a microscopic junction. Protection works in layers: on the chip, every input pin has clamp diodes that steer a surge harmlessly to the supply rails; on the board, you add TVS (transient-voltage-suppression) diodes, series resistors, and ferrite beads at the connectors where the outside world plugs in; in the factory, people wear grounded wrist straps and work on dissipative mats so charge never builds up in the first place.
ESD protection matters because the damage is often invisible and delayed: a zap may not kill a part outright but weaken it, so it fails weeks later, a so-called latent failure, which makes ESD a reliability problem and not just a handling nuisance. It is also a required part of EMC immunity testing, where a calibrated ESD gun fires standardized zaps at every exposed surface and connector. Honest note: those tiny on-chip clamp diodes protect a chip during handling, but they are NOT meant to absorb large real-world surges in the field, so exposed connectors need their own beefier external protection.
A USB connector exposed to fingers gets a small TVS-diode array across its data lines. When an 8 kV static zap hits the plug, the TVS clamps the spike to a couple of volts and shunts the current to ground, so the chip's data pins never see the lethal voltage.
Clamp the spike at the connector, before it ever reaches the chip.
Handle CMOS parts on a grounded mat with a wrist strap — ESD damage is frequently latent, weakening a part that then fails later, so a board that works on the bench today may already be wounded.