ESD-induced latchup-like failure in a touch panel control IC

With on-chip ESD protection design, the I/O pins of a touch panel control IC can pass the chip-level ESD tests of HBM 4kV and MM 400V. However, such a touch panel control IC mounted onto a display panel suffered the latchup-like failure after the system-level ESD zapping in the air-discharge mode. Some high-voltage power pin began to generate a large leakage current after the system-level ESD test, which demonstrated a symptom of latchup failure. By failure analyses with TLP-measurement, EMMI, and SEM, the root cause has been found on the power-rail ESD clamp circuit of the high-voltage power pin. The holding voltage of the power-rail ESD clamp circuit in the high-voltage power pin, that was lower than its normal operating voltage, caused such a latchup-like failure. Some modified solutions to rescue this latchup-like failure in the touch panel control IC are presented.