A DC-DC converter has high-side power and low-side power transistors connected in series between supply terminals, an inductor connected between the power transistors and an output terminal. A comparator compares the output voltage with a reference voltage. A detector detects when inductor current approaches zero. A timer is configured to determine a minimum ON time of the high-side power transistor optimized for a particular value inductor. A current detector detects current flow in the back-gate diode of the low-side power transistor. timer is configured to determine an overriding ON time in response to the back-gate current detector. Logic provides control signals to gate power transistors in response to the comparator and the longer one of the minimum ON time and the overriding ON time. The minimum ON time for the high-side power transistor is adjusted in response to the actual inductance of the inductor.