ESD Protection Chip – Understanding Clamping Voltage

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 – 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.

Almost every charger and regulator out there nowadays has an absolute max of 6V. If you have a USB rated TVS and some capacitance on the 5V bus, you probably won't have problems there. You can use a high voltage cap if you want, and put it close to the barrel jack.

For buttons, use a series resistor (as large as you can accept without causing problems with your pullup or pulldown) and a shunt cap. Put the resistor near the button and put the cap near the IC where the signal goes. You probably don't need TVS on the buttons, but it is a good idea to put it in the layout (close to the IC) in case it is needed. A wide variety of 0402 sized ESD diodes are available. If you have a large series resistance between the ESD gun and the IC, the ESD diode will not have to dissipate much energy. The capacitor will help prevent steep dV/dt.

Most importantly, you need to test. You can't solve ESD analytically. You can give it your best shot, but then you need to test to verify.

The two main problems you get from ESD are:

1. IC or transistor inputs damaged (fix with capacitance or ESD diodes or TVS)
2. poorly terminated inputs toggle due to pulse coupling and cause some undesired behavior such as reboot/reset/poweroff.

Rarely does ESD damage anything other than an IC input.

Also make sure you consider case 2. Any reset inputs or interrupt inputs need to be scrutinized. An internal 200k (or whatever) pullup may not be enough. You may want to add either a cap, or a stronger pullup/pulldown.

Finally, the best defense against ESD, when possible, is to keep the gun away from the components by recessing them within a plastic housing. That is mainly a mechanical design issue, though. If the gun tip cannot get near the components, there will be no discharge in the first place.