HMI (Human Machine Interface) communication port common mode choke selection?

The selection of a common-mode choke for HMI communication ports depends on the communication type, data rate, and the interference frequency bands that need to be suppressed. Key parameters include: differential-mode inductance, common-mode impedance frequency curve, rated current, DC resistance, and impedance. For low-speed interfaces such as RS485 and CAN, with data rates below 1 Mbps, models with differential-mode inductance values ranging from tens to hundreds of μH can be selected, such as the CMZ3225A series, whose common-mode impedance peak value is typically in the range of several MHz to tens of MHz. For high-speed interfaces such as USB 2.0 (480 Mbps) and Ethernet (100/1000 Mbps), models with good high-frequency performance should be selected, with a high common-mode impedance in the range of tens to hundreds of MHz, such as the CMZ2012A-900T, while maintaining a very low differential-mode inductance to avoid affecting signal integrity. The rated current must be greater than the maximum current flowing through the signal line. The DC resistance (DCR) should be as low as possible to reduce signal attenuation. The package size must comply with PCB space constraints. When selecting a choke, refer to the impedance-frequency curve provided by the component supplier and choose the model with the highest impedance at the frequency where interference exceeds the standard or at a multiple of the communication frequency. Etymotic's CMZ series common-mode chokes offer a variety of specifications, covering applications from low speed to high speed. Engineers can make precise selections based on the signal characteristics of specific ports and EMC test results.