How to select protection devices for HMI (Human Machine Interface) interfaces?

When selecting protection devices for various HMI interfaces, a systematic consideration of the threats they face and the circuit characteristics is necessary. Protection devices mainly include TVS/ESD diodes, varistors, gas discharge tubes, and resettable fuses. The selection process is as follows: First, identify the interface type and threat: ESD, surge, overvoltage, or overcurrent. Determine the normal operating voltage and maximum withstand voltage of the protected circuit. For high-speed signal interfaces, such as USB and HDMI, prioritize low-capacitance TVS/ESD arrays, such as the ESDLC series, with a capacitance value less than 1pF. For power ports, such as DC 24V input, select TVS with high current carrying capacity, such as SMCJ24CA, or a combination with a varistor.

For surge protection of communication ports, such as Ethernet and RS485, a multi-level protection scheme using GDTs and TVS is often employed. For hot-swappable or potentially short-circuited ports, consider PPTC resettable fuses for overcurrent protection, such as the SMD2920 series. The response time of all protection devices should be faster than the rise time of the threat. Package selection must meet PCB space and power consumption requirements. The final selection should be based on the specific test standard level. Eternity offers a full range of protection devices, along with selection tools and reference designs, to help engineers choose the most suitable protection scheme for each interface of the HMI.