A high efficiency, noninverting, buck-boost DC-DC converter

Portable electronics applications often require a system voltage that is within the range of fully-charged to semidischarged batteries, for example 3.3 V output from a 2.8 V to 4.2 V lithium-ion battery input. The optimal solution to this requirement is a high-efficiency, noninverting buck-boost, DC-DC converter, providing a programmable constant output voltage, typically from single cell Li-ion, multicell NiMH, or alkaline power sources. This solution uses a control scheme which provides automatic and smooth transition through boost, buck-boost and buck modes.