Current-mode step-down/step-up DC-DC controller

The invention discloses a current-mode step-down/step-up DC-DC controller. Even if an input voltage is very close to an output voltage, the controller still can work efficiently. The input, ground and output ends are selectively connected to a switch of an inductor terminal, and are controlled in a step-up/step-down region, so as to alternately serve as a step-down converter and a step-up converter. Therefore, the number of switches which repeatedly change the states will be reduced, thereby reducing the switching loss and improving the conversion efficiency. In a working process, a current passing through an inductor is sensed, and is compared with an error value, thereby controlling the switching from a step-down mode to a step-up mode and the switching from the step-up mode to the step-down mode.