How to match the common mode inductor of the I/O module?

Matching common-mode inductors to I/O modules requires comprehensive consideration of impedance characteristics, current capacity, and circuit topology. First, determine the center frequency of the common-mode noise to be suppressed through testing or estimation, and select the inductor with the highest impedance at that frequency. For example, for 30-50MHz noise, a CMZ3225A-510T can be selected. The rated current must be greater than the operating current flowing through the inductor, and saturation current must be considered to prevent core saturation under high current, which could lead to a sudden impedance drop. When using common-mode inductors on differential signal lines, ensure that their differential-mode impedance is sufficiently low to avoid affecting signal quality; refer to the differential-mode insertion loss in the S-parameters.

In circuit topology, common-mode inductors are usually used in conjunction with Y capacitors; the capacitor value should be chosen to create a notch filter effect against noise frequencies. During installation, ensure that the two windings of the common-mode inductor are wound symmetrically to reduce the differential-to-common-mode effect. For high-frequency noise, ferrite materials with higher permeability or multilayer chip inductors can be selected. In actual circuits, the matching effect can be verified by comparing the conducted interference test results before and after adding the common-mode inductor.