Double-check the data for the thermistor you have. Even if it has a table, they often will specify R25 and a "Beta" or "B" value. R25 is the resistance at 25C. B or Beta is a parameter you can plug in to a log equation to solve for the resistance at any temp (you also need to plug in the R25...
It depends on a lot of stuff. The safest thing, if you can afford it, would be to mux the whole entire bus so that when it is used for your 3.3V device, the SDRAM is completely isolated. You could use a FET bus switch for the SDRAM, and a level-shifting FET bus switch for the 1.8V device. Place...
The series diode should work fine. If you put a resistor to ground as a load on the charge-pump side of the diode, any reverse current that flows through the diode will have a path to ground, and there will therefore not be any problem with over-voltage at the charge pump output. If there is a...