How to eliminate common-mode interference on the RS485 interface of the edge box?

Common-mode interference at the RS485 interface of the edge box is mainly caused by ground potential difference and spatial coupling, manifesting as communication errors or port damage. The elimination solution uses the Audiotronics bus-specific TVS array ESDSM712, named SM712, with 7V and 12V dual shutdown voltages. It adapts to RS485 differential signals, clamping A-line to ground and B-line to ground respectively. It also integrates two unidirectional TVS junction capacitors with a capacitance of only 5pF, without reducing signal rate. It is paired with a common-mode inductor CML3225A-510T. The model information for this ferrite bead is: CML is a common-mode inductor, 3225 is 3.2×2.5mm, and 510T indicates a 51μH inductance, providing ≥25dB common-mode attenuation in 1-100MHz. Furthermore, the PCB layout should ensure equal length for A/B differential shielding, use single-ended grounding, and provide primary coarse protection through a 3R090L-6X8 gas discharge tube. This device is a through-hole three-terminal type; 090 indicates an operating voltage of 90V; and 6X8 is 6×8mm in size, conforming to IEC61000-4-4. The 2kV EFT test showed a communication bit error rate of less than 10^-9, effectively eliminating common-mode interference.