How to optimize the filtering of the operating loop of a power FTU?

The filtering of the operating loop needs to balance high-frequency interference suppression and signal integrity. The optimized solution employs targeted filtering components. For digital inputs, an RC filter (1kΩ + 100nF) with a time constant of 10ms is used, coupled with ESD5V0D8B bidirectional ESD protection. For relay drive outputs, a PBZ1608A-102Z0T ferrite bead (1000Ω@100MHz) is connected in series, with a 1N4007W freewheeling diode in parallel. Analog operating signals use a second-order active filter, with an AD8629 operational amplifier and a cutoff frequency of 1kHz. In the PCB design, the filtering circuit is placed close to the connector and uses star grounding. Shielded twisted-pair cables are used, with the shield grounded at a single point. Through this optimization, the operating loop's immunity is improved, and the false alarm rate is reduced to below 0.001%, meeting the IEC 61000-4-6 conducted immunity 10V test requirements.