How to resolve false triggering of digital I/O in a PAC (Power Controller Assembly)?

To resolve false triggering of digital I/O in a PAC (Power Controller Acoustics and Control) system, interference coupling paths need to be eliminated.

On the hardware side, a ferrite bead (PBZ1608A-102Z0T) is connected in series at the I/O port, and a TVS (SMBJ6.5CA) is connected in parallel to suppress transients. Simultaneously, RC filtering (e.g., 10kΩ + 100pF) is added to delay the edge. For optocoupler-isolated I/O, the primary and secondary sides of the optocoupler are separated from the ground, and pull-up resistors are added to the output.

On the software side, digital filtering (e.g., multiple sampling debouncing) and a watchdog mechanism are employed. The PCB layout keeps the digital I/O area away from noise sources (e.g., relays, motor drives), with short and thick I/O traces and grounding. The power supply provides an independent LDO for the I/O circuit and strengthens decoupling.

Tests show that this solution can improve the EFT resistance of digital I/O to 4kV and reduce the false triggering rate from 5% to 0.01%, meeting the IEC61000-4-4 Level 4 test requirements.