An inductor has first and second terminals. A first switch is coupled between the first terminal and a voltage supply terminal. A second switch is coupled between the first terminal and a negative output supply terminal. A third switch is coupled between the second terminal and a positive output supply terminal. A fourth switch is coupled between the second terminal and a ground terminal. A controller is coupled to the first, second, third and fourth switches. The controller is configured to provide: an inductor charge mode; a positive boost mode; a negative boost mode; a first rest state in which the controller closes the first switch and opens the second, third and fourth switches; and a second rest state in which the controller closes the fourth switch and opens the first, second and third switches.