I've got some DACs that I'd like to switch gain ranges on, and it turns out I can do it nicely using a single 2N7002 (sot23 n-channel mosfet) to switch a resistor to ground in each reference circuit. So I'd like to turn each 7002 on and off from a pin on an XC3S400. But
3.3 volts is a marginal high for this fet... 4 volts looks safe.So, how about running Vccio a bit high, 3.5 maybe, and adding an external pullup resistor to +5. If I tristate the pin, I should forward-bias the upper esd diode and get 4.2 roughly, right? I'm thinking maybe a half milliampere or so pullup current. Doing this 8 times only dumps 4 mA into the Vccio rail, no hazard there.
I could use a lower-threshold fet, I guess, but the 7002's are in stock and cost 3 cents each.
John