How to select the appropriate filter for the communication port of a power FTU?

Communication port filtering selection is based on signal frequency and interference spectrum.

RS485: CMZ3225A-510T common-mode inductor (510μH), cutoff frequency 100kHz. Ethernet: CMZ2012A-900T common-mode inductor (90μH), cutoff frequency 10MHz.

Wireless module: PBZ1608E600Z0T ferrite bead (600Ω@100MHz).

Protection device selection: ESDSM712 for RS485, ESDLC3V3D3B for Ethernet, and ESDLC5V0D9B for wireless.

PCB layout: Filtering components are placed close to the interface with short leads.

With proper selection, port filtering attenuates by more than 30dB in the target frequency band, meeting the IEC 61000-4-4 EFT test requirements.