I am having a hard time understanding this logic. Please bare with me if my question is very basic. I would appreciate if someone can explain what is happening?
If I look into any typical TVS IC data sheet, I would see a similar design to the following:
For example the above is the circuit for SRV05-4.
I can understand what happens in general, but not the details. For example, pin 5 is usually tied to a 3.3 voltage source on the board. And pin 2 is obviously the ground. And, pin 1,3,4,6 are the input pins. The first question is that I know if we apply let's say a huge spike of (-20 V) on pin 1, then the lower most left diode will protect it by pushing it down to zero. But what happens to the huge voltage spike? Shouldn't the diode have a forward bias of about 0.7 volt? So, what is exactly happening? How does this -20 volt being taken care of? What is the voltage drop across the diode in such case?
And, more importantly, how come there is only Zener diode in one direction and not the opposite direction? My guess is it is there in case if the voltage on pin 5 suddenly rises for some reason, and it will clamp the voltage. But what about a case that it suddenly falls to a very low voltage? Shouldn't we have a protection on the other direction as well? How come they see it as a possibility for voltage on pin 5 to rise very high, but not to fall very low?