Anomalous latchup failure induced by on-chip ESD protection circuit in a high-voltage CMOS IC product

Latchup failure induced by ESD protection circuits occurred in a high-voltage IC product. Latchup occurred anomalously at only several output pins. All output pins have nearly identical layouts except the side output pin has a N-well resistor of RC gate-coupled PMOS beside. It was later found this N-well resistor is the main cause of inducing latchup.