How to suppress radiated interference from power FTUs?

The main sources of radiated interference from the FTU are the switching power supply, clock circuit, and high-frequency digital signals. The solution combines source suppression with shielding. A low-radiation topology, such as a resonant LLC, is used in the switching power supply, with RC absorption (220Ω + 470pF) added to the MOSFET. The clock circuit uses spread spectrum technology with a spread spectrum range of ±2%. A PBZ1005B-501Z0T ferrite bead (500Ω@100MHz) is connected in series to the digital interface. The chassis is made of 6063 aluminum alloy, 1.5mm thick, with beryllium copper springs used in the gaps, providing a shielding effectiveness greater than 40dB@1GHz. All cable entry points are equipped with shielded filter connectors, such as the CX-2020 series. The PCB layout places high-speed signals on the inner layers, with ground copper on the outer layers. With this solution, radiated emissions in the 30MHz-1GHz band are more than 10dB below the EN55032 Class B limit, meeting the IEC 61000-4-3 radiated emission test requirements.