How to select the filter for the communication port of a concentrator?

The selection of filtering components for various communication ports (RS485, CAN, Ethernet) of the concentrator must be determined based on signal rate, interference type, and test level.

Common-mode inductors: For RS485/CAN (<1Mbps), select CML3225A-510T (51μH); for Ethernet (100Mbps), select CML2012A-900T (90μH) or an integrated filter connector.

TVS diodes: Select the turn-off voltage VRWM according to the line operating voltage; for example, select SMBJ5.0CA for 5V lines and SMBJ24CA for 24V lines. Select the peak current Ipp according to the surge test level; for example, Ipp>100A (8/20μs) is required for 4kV surges.

Resistors and capacitors: Used for RC filtering, with resistance values of 22-100Ω and capacitance values of 100pF-1nF.

Note the impact of capacitors on signal edges. All filtering components should be surface-mount packages to reduce parasitic parameters and should be placed close to the connectors. Proper selection ensures effective filtering without affecting communication quality.