Mix-voltage conversion for single-inductor dual-output buck converters

A single-inductor dual-output (SIDO) buck converter has recently found applications in hand-held battery-powered electronic devices. The circuit operation and the functional interdependencies among basic converter parameters such as DC voltage gains, transistor duty cycles, and load current levels are much more complicated than those of the single-output counterpart. In this paper, a rigorous analysis was conducted to develop DC equations for the converters. More importantly, from the analysis results, a possibility of a new mode of operation, dubbed “mix-buck” operation, will be pointed out. In the so-called “mix-buck” operation, the converter is capable of working even when the input voltage is lower than one of the two output voltages. In the past, a SIDO buck converter has been used for providing “pure-buck” outputs, i.e., both output voltages are lower than the input voltage. Therefore, this possibility not only opens up new applications but also may extend the operating battery range in existing applications. Experimental results confirmed the DC equations and the “mix-buck” operation of SIDO converters.