Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts. It only takes a minute to sign up.
Sign up to join this community
I've looked at articles detailing I2C level shifting and referencing the below figure I have a question.
If the gates of the FETs were driven by 2.5V and everything else remained the same, would the level shifting still work?
I would think a low from the 3.3V side would propagate but a low from the 5V would not get through.
At what low-side voltage or gate voltage would this circuit not work?
thanks
The FETs activate when their gate voltage, relative to the source, is sufficiently above the gate threshold voltage. (The threshold voltage is specified for a very small drain current, such as 250 µA; here, we need more current for the pull-up resistors. The gate voltage we want is the one for which the datasheet specifies RDS(on).)
The low-voltage side can activate the FETs by driving low the source.
The high-voltage side can activate the FETs by driving low the source through the body diode, which adds about 0.7 V.
So this circuit will work with a gate voltage of 2.5 V as long as the FETs fully switch on at 1.8 V.
