I intend to protect a BUS switches ICs, whose voltage on its pins cannot exceed 5.5V and 3.3V. The current cannot exceed 16mA.
The circuits needs to opperate from 3.3V to 5V. But automotive enviroment will need protection for continuous 14,8V at the input. So, I'm using a voltage-clamp to prevent against overvoltage, a resistor to prevent against overcurrent and a TVS diode to prevent against ESD.
The problem is to choose TVS diode. A TVS with voltage breakdown below 14,8V would burn at continous voltage. So, the voltage breakdown needs to be greather than 14,8V. For a TVS with this value of voltage breakdown, I didn't find one with clamping voltage smaller than 21,5V and I'm afraid that a resistor of of 360/0.5W will not be enough.
For 5V signal-line: (21.5-5)^2 /360 =0.756 W
For 3.3V signal-line: (21.5-3.3)^2 /360 =0.920 W
The question is:
I suppose the ESD events are very short in time, will it be enought to fry the resistor of 360/0.5W ?
The problems to choose greather values for resistance are the interference on communication line and the size of resistors that will ocupy more space on the PCB.