How to ensure EMC of PAC intelligent controller CAN/RS485 bus?

Ensuring EMC of the CAN/RS485 bus for the PAC (Power Controller Assembly) requires addressing interface protection, filtering, and grounding. Interface protection employs a three-stage approach: a first-stage gas discharge tube (e.g., 2R090L-6×8) absorbs surges; a second-stage TVS diode (e.g., SMBJ6.5CA) clamps transient voltages; and a third-stage series resistor (e.g., 10Ω) limits current. For filtering, a common-mode inductor (CML3225A-510T) is used at the bus entry point to suppress common-mode noise, and a π-type filter circuit is reserved. During PCB routing, CANH/CANL or 485A/485B differential pairs must be strictly of equal length, tightly coupled, and kept away from power lines. The shielded twisted-pair cable shielding layer is terminated 360 degrees at the interface to the metal casing, which is then connected to the chassis. A 120Ω bus termination resistor is used for matching and placed after the common-mode inductor. Testing has verified that this design enables the CAN/RS485 bus to pass IEC61000-4-2 ESD 8kV and IEC61000-4-4... EFT 4kV and IEC61000-4-5 Surge 1kV tests show a bit error rate of less than 10^-9;