How to match the common mode inductor of the motion controller MC

Matching a common-mode inductor to a motion controller (MC) requires consideration of noise frequency, current, and circuit impedance. First, determine the center frequency of the common-mode noise to be suppressed and select the inductor with the highest impedance at that frequency. For example, for switching noise of several hundred kHz, the CMZ3225 series can be used. The rated current must be greater than the actual operating current, and the saturation characteristics under peak current must be considered to prevent impedance drop due to core saturation. When using a common-mode inductor on differential signal lines, its impact on signal integrity must be evaluated, and the differential-mode insertion loss must be measured to ensure it is acceptable.

In circuit matching, common-mode inductors are usually paired with Y capacitors. The choice of Y capacitor value, together with the inductor, forms a resonant point at the noise frequency, which should be avoided at the signal frequency. During installation, pay attention to winding symmetry to reduce differential-mode to common-mode effects. For high-frequency broadband noise, multilayer chip inductors or ferrite bead arrays can be selected. After matching, conducted interference tests should be performed to compare the spectrum before and after matching to verify the suppression effect. Based on the test results, the inductor parameters or parallel damping resistors should be fine-tuned.