How can grounding of a power FTU system improve its immunity to disturbances?

System grounding optimization significantly improves FTU immunity. A hierarchical grounding architecture is adopted: Level 1 is chassis grounding, directly connected to earth; Level 2 is power ground, connected to the chassis via a low-impedance path; Level 3 is signal ground, connected to power ground via ferrite beads. A star topology is used for grounding to avoid ground loops. PCB design: Analog ground uses a single-point star ground; digital ground uses a copper grid; both are connected via ferrite beads. Cable shielding is grounded at both ends and connected to the chassis via shielded connectors. This system grounding improves common-mode immunity by 30dB, meeting the IEC 61000-4-6 10V conducted immunity and IEC 61000-4-4 4kV EFT test requirements.