I am designing a a board based on a microcontroller that have differential analog pins. The data sheet says that although the MCU's ADCs are internally protected against ESD strikes I must still take care to prevent the the input does not exceed the voltage and current limits of the pins which is Vcc (3.3 V) and +- 10mA. I am also planning to tie the Vref to 1.5 V. The analog pins will be both used in single ended and differential mode depending on the situation.
Doing a bit of reading, the conventional way seems to be placing diodes.
simulate this circuit – Schematic created using CircuitLab
Since my Vref is set to 1.5 volts anything beyond that and cutting it beyond 3.3 V would destroy the pin. So anything in between should where diode cut-off the voltage. Would say at 2.5 V would be good point? But looking for parts I'm greeted by three identical sounding specifications Reverse Standoff, Breakdown, Clamping. Which specification is the one I should look at?
For current, since assuming we successfully find a part that will keep the input voltage at 2.5 V I should also adjust R1 and R2 so that it won't exceed 10mA.
R = V/I R = 2.5/0.010 R = 250 Ohms
It should not be less than 250 ohms. Am I approaching this correctly?