This is a question about 3.3V IO pins generally but I guess the answer
is likely to be useful to other beagleboners.
I'm trying to add TVS diodes to a 3.3V microcontroller input.
The trouble is, The diodes with the lowest reverse breakdown (V_BR)
and reverse stand off voltage (V_R) numbers also have substantial
reverse leakage I_R @ V_R.
For example the Littlefuse SAC5.0 has 300 uA leakage at 5.0V.
The inputs to my circuit have only about 500 uA flowing to ground
when they are high, so these TVS diodes might substantially load
the circuit. Unless the reverse leakage is much lower down at
3.3 V than at 5V, but the spec sheet doesn't seem to specify that.
If I go to diodes with higher V_R the I_R gets much better:
TVS Part I_R @ V_R (uA)
Littlefuse SAC8.5 50
Littlefuse SAC10 5
Littlefuse SAC12 1
I don't know what common practice is here. I guess since 3.3V TVS aren't
really available (the ones that advertise themselves that way still seem
to have 5V standoff when you look at specs), people use higher V_R to get
protection from short transients?
Any help or advice greatly appreciated,