How to select a common-mode choke for industrial servo communication?

When selecting a common-mode choke for servo communication ports (such as CAN, RS485, EtherCAT), a balance between signal integrity and EMC performance is necessary. The selection steps for Etymotic are as follows:

1) Determine the signal rate: CAN FD up to 5Mbps, EtherCAT 100Mbps. Select the effective bandwidth of the choke accordingly, ensuring minimal impedance attenuation (<3dB) at the signal frequency.

2) Determine the common-mode interference frequency: typically the switching frequency harmonics (tens of kHz to tens of MHz). The choke should have high impedance (>100Ω) in this frequency band.

3) Consult the datasheet: Select series such as CML3225A (signal) or CMZ2012A (power supply), paying attention to low DC resistance (DCR) to avoid voltage drop, and ensuring the rated current meets requirements.

4) Consider parasitic capacitance: For high-speed applications (such as EtherCAT), select a model with low parasitic capacitance (<10pF). For example, selecting CML4532A-510T (51μH, DCR~0.3Ω, bandwidth>20MHz) for CAN FD can effectively suppress common-mode interference below 30MHz without affecting the 5Mbps signal quality.