Patent ID: 6965838

Claim:
Apparatus comprising: a semiconductor having an output node which sources current to a first load; a controllable load coupled to the output node of said semiconductor and having at least two controllable states of operation including an on state in which a predetermined current load is drawn from the output node of said semiconductor in addition to the first load; and a controller which is coupled to said semiconductor and said controllable load and which (1) senses the voltage across the output node of said semiconductor and a second node of said semiconductor on at least three points in time designated herein as T 1 , T 2 , and T 3 wherein the controller (2) activates the on state of said controllable load during T 2 and (3) derives a first calculated voltage as a function of the voltages sensed at T 1 , T 2 and T 3 and (4) calculates the on-resistance of said semiconductor by dividing the first calculated voltage by the predetermined current.