How to select the TVS diode for the PMS interface of an electrical power measurement switch?

When selecting TVS diodes for each PMS interface, key parameters must be determined based on the operating voltage, signal type, and required surge/ESD test levels of the protected circuit.

First, determine the TVS's turn-off voltage (VRWM): VRWM should be slightly higher than the maximum normal operating voltage of the protected line. For example, for a 5V circuit, a VRWM=5.0V SMBJ5.0CA diode can be selected.

Second, determine the clamping voltage (VC): Under the maximum peak pulse current (Ipp), VC should be lower than the maximum withstand voltage of the protected device.

Then, determine the required Ipp value according to the test standard (e.g., IEC 61000-4-5) and select a TVS model that meets this Ipp requirement; generally, higher power outputs require higher Ipp values. For bidirectional interference (e.g., AC lines), a bidirectional TVS (CA suffix) should be selected; for DC lines, a unidirectional TVS (A suffix) is sufficient. Junction capacitance (Cj) must also be considered: for high-speed signal lines (e.g., USB, Ethernet), a low-capacitance TVS (e.g., ESD5V0D3B, Cj<50pF) should be selected.

Finally, the package must be suitable for the PCB layout and power consumption requirements. A properly selected TVS can reliably protect the interface without affecting signal quality.