How to match the protection device for the PAC interface of the intelligent controller?

When matching protective devices for the PAC interface of an intelligent controller, voltage, current, and response time must be considered.

First, determine the operating voltage (e.g., 24V), and the breakdown voltage of the protective device must be 20% higher than the operating voltage (e.g., 30V).

Second, estimate the threat current (e.g., EFT 100A) and select a device with a withstand current greater than the threat current (e.g., TVS peak pulse current 200A). Regarding response time, gas discharge tubes are slower (~100ns) and used for the first stage; TVS is faster (<1ns) and used for the second stage. Simultaneously, pay attention to the capacitance of the protective device; high-speed interfaces require low-capacitance TVS (e.g., ESDLC5V0D3B).

In terms of layout, the first stage should be close to the interface, and the second stage close to the chip. After matching, the interface should pass the corresponding level tests of IEC61000-4-2/4/5 without affecting signal integrity.