How to select the right TVS diode for a power FTU interface?

The selection of the TVS diode for the interface is based on the operating voltage and transient energy. Power port: For a 24VDC system, select SMBJ24CA, VRWM=24V, VBR=26.7V, IPP=20A. Communication port: For RS485, select SMBJ6.5CA, VRWM=6.5V. Signal port: For 5V signals, select SMBJ5.0CA. Selection principles: VRWM slightly higher than the operating voltage (1.1-1.2 times); IPP greater than the expected surge current; junction capacitance should not affect the signal (for high-speed signals, select low capacitance types, such as the SMBJ series <100pF). Installation: Close to the interface, short leads. With proper selection, the TVS can effectively clamp overvoltages and protect downstream circuitry.