Mine's the GSOT03C, for 3v3 systems.; versions exist with higher breakdown voltages.
I never use these by themselves. For low-speed inputs, I start with a small capacitor straight across the input pin and input GND, followed by a current limiting series resistor, then the GSOT03C with a parallel capacitor to system GND, then another series resistor, a pull-up/down resistor to retain a valid logic level even if the input line is broken, and finally a dedicated Schmitt trigger gate. Adjust for higher speed inputs; in some cases it makes sense to substitute a polyfuse for the first series resistor.
JDB.
[Context: this is for industrial applications, and intended to protect as much against ESD as against inexperienced personnel doing board-level work and hooking up 24V to the wrong pin. In other words: this is for when potential downtime is more expensive than a handful of parts per I/O pin]
Many thanks! My application is both slow and non-critical (nothing exciting, but I will post about it when it's done), and it looks like the higher voltage versions will work nicely.
