One of my project architectures looks like this:
GPIO / 595 output / 12 VDC wire lengths will not exceed 25 cm.
I have faced MCU lockup issues due to EFT in the past and want to make sure this design is protected against all such threats.
This is what I intend to do for protecting my system:
1) Protection against surges - MOV on the input ac lines in the ac DC converter circuit which handles 4 kV surges. Do I need to do anything more besides this? I have heard that TVS diode offers better protection due to fast reaction time but MOV turns out to give best performance per unit money.
2) EFT/ESD - TVS diode (uni-directional) between 12V and GND at the entry point on main board (PCB which has MCU, 595 and relay). Uni-directional TVS diodes on all GPIOs leaving the board in form of wires.
There are some GPIOs that control 74HC595. Do I need to put TVS diodes on those GPIOs as well? Or should I put TVS diodes on the 595 output wires? Or both GPIO and output wires?
For DC lines, is uni-directional TVS diodes OK?
For such a system, what values of breakdown voltage, standoff voltage and peak power should I select? - for 12 VDC power line and 3.3 VDC GPIO lines.