Disclosed herein are an apparatus for controlling a switch-mode power supply, and a method of operating the same. In an embodiment, it is determined whether or not a current of an inductor of the switching power supply has become less than or equal to a predetermined value. In an embodiment, a variable reference voltage is adjusted based on the current of the inductor and an output voltage. In an embodiment, a switch is turned off based on the inductor current, the output voltage, and the variable reference voltage.