When a vendor specifies an Rds(on) value for a part I have seen typical and max values specified but never minimum values. I understand that Rds(on) is a function of temperature and gate to source voltage (Vgs) but for a given temperature and Vgs is the variance of Rds(on) basically an intrinsic of the MOSFET design? How much does the Rds(on) vary from FET to FET of the same kind at a given operating point?
What motivates this question is current limit sensing of the drain to source voltage (Vds). I can measure Vds and approximate a current if Rds(on) is known. However if Rds(on) varies too much the current limit sensing may erroneously report no fault with a huge current.