ESD Protection Circuit Design for Mixed PCBs
Electrostatic discharge almost never shows up as a clean, dramatic failure on a mixed-signal PCB. There is usually no burnt component, no obvious short, no instant death. The board powers on. Firmware runs. Interfaces appear functional. That is precisely what makes ESD so dangerous in real products. The damage is often cumulative and indirect. A unit works on the bench, passes production test, and even survives early validation. Weeks later, after installation, handling, or repeated cable insertion, odd behavior begins to surface. A controller resets under seemingly random conditions. A communication link drops once a day. An analog reading spikes for no clear reason. In many mixed-signal designs, these are the first signs that the ESD protection circuit strategy was either incomplete or ineffective.
