A 90% peak efficiency single-inductor dual-output buck-boost converter with extended-PWM control

Power management in portable devices demands small size, low cost as well as long battery lifetime, which in turn drive the development of single-inductor multiple-output (SIMO) converters. Due to the battery voltage variation during usage and the wide-range dynamic voltage scaling (DVS) applied for power reduction, high-efficiency buck-boost conversion is required to extend the battery lifetime. The buck-boost converter selects the operation mode by comparing the output with the supply voltage, which is not suitable for multioutput converters. The reported single-inductor dual-output (SIDO) buck-boost converter uses a state machine with sophisticated current sense for mode selection and requires a freewheeling state that dissipates energy. The converter uses one additional auxiliary inductor for step-up/down mode adjustment. This paper proposes an extended-PWM (EPWM) control which automatically selects buck or boost mode and facilitates smooth mode transition. It is suitable for flexible outputs and maintains a high efficiency in buck and in boost converters.