Analysis and Design of Mixed-Mode Operation for Noninverting Buck–Boost DC–DC Converters

A noninverting buck-boost dc-dc converter can work in the buck, boost, or buck-boost mode, but it has been analyzed that operating in the buck-boost mode has the lowest efficiency. However, if the buck-boost mode is excluded, the converter may jump between the buck and boost modes when the input voltage approaches the output voltage. This transition region is called the mixed mode, and larger output voltage ripples are expectable. In this brief, the conditions for the converter to operate in the mixed mode are analyzed, including the impact of mismatches between ramp signals, and a ramp generator is designed accordingly. Moreover, a full-cycle current-sensing circuit is proposed, and it can effectively inhibit the switching noise on the sensed current signal. The proposed chip was fabricated by the 0.35-μm 2P4M 3.3-V/5-V mixed-signal polycide process. The maximal measured efficiency is 93.5%.