For pull-up resistor of I2C, I have found formula to determine R(min).
For a device with; 0,4 VOL(MAX) at 3mA IOL The calculation can be done for VDD = 5V:
R(min) = (5V - 0,4) / 3mA = 1533 ohm.
The thing i cannot understand. Here we assume that over the transtor; there will fall 0,4V and 3mA, when using this resistor. But we do not know exactly if we use 1533 ohm, that 3 mA will flow so 0,4V will fall.
It could also be that there will fall much lower voltage; lets say 0,2V at 1,5mA (or higher voltage and current)
Then R(min) = (5V - 0,2) / 1,5mA = 3200 ohm.
So the question is; how do we know that there will fall exactly 0,4V when we use 1533 ohm, so 3mA will flow. Is this an approximation we do? because we truly need loadline and characterics to do this exactly?