Reducing the clamping voltage of a TVS diode
You can look at Zener diodes instead of TVS diodes for lower clamp voltages (but worse power handling.)

How bad an input spike on the 5V rail would you want to worry about? Or do you have higher input voltage? You could put a non-LDO regulator with a high voltage rating (like LM350 or whatever) before the 5V, so that the 5V will already be well regulated. A normal TVS will clamp well below the 35V rated input voltage of the LM350.

However, if your power input, which may contain the spike, has to be 5V, then this won't work.

Another option is a resistor/Zener. A 2 Ohm resistor will drop 1V at 500 mA. Follow that by a 5.1V Zener and your regulator, and precede it with the TVS, and you'll have a somewhat more robust system. The TVS takes care of the really bad spikes; the resistor+Zener takes care of getting the voltage "in range" without blowing up, and the regulator can then regulate.







simulate this circuit &ndash; Schematic created using CircuitLab

Disclaimer: I'm a hobbyist. If someone who does this for a living tells me otherwise (and why/how,) I will gladly concede I'm wrong :-)

So, consider a 7V spike makes it past the TVS. This means the Zener needs to be rated for 1A temporary dissipation to survive.