How to control differential-mode conducted interference in a motion controller (MC)

To control differential-mode conducted interference in the motion controller MC, effective filtering is needed along the noise propagation path. Differential-mode noise mainly propagates between power supply LN lines or signal lines. A π-type filter network should be designed at the power input, where the differential-mode inductor can be a ferrite core or a multilayer choke, such as a PWR series power inductor, working in conjunction with an X capacitor to attenuate differential-mode noise. Calculate the filter's cutoff frequency to ensure it is below the lowest noise frequency. For differential-mode ripple generated by the switching power supply, an LC filter can be added at the output, with the inductance selected based on the ripple current and allowable voltage drop.

On signal lines, impedance-matched terminating resistors should be installed for high-speed differential pairs, and a small resistor should be connected in series at the drive end to mitigate edge noise and reduce high-frequency components. During PCB layout, power traces should be as short and wide as possible to reduce loop inductance. The grounding terminals of all filter capacitors should be connected to a low-impedance ground plane via the shortest path. Verify the control effect through conducted emission testing, focusing on the 150kHz to 30MHz frequency band. If specific frequencies exceed the limits, filter parameters can be adjusted or the number of stages increased.