Patent ID: 8773084

Claim:
A DC-to-DC, buck-boost voltage converter, the converter comprising a first buck switching transistor coupled between an input voltage and a first terminal of an inductor, a second buck switching transistor coupled between the first terminal of the inductor and ground, a first boost switching transistor coupled between a second terminal of the inductor and ground, and a second boost switching transistor coupled between the second terminal of the inductor and an output terminal of the converter, the converter comprising: a duty cycle controller configured to generate control signals for a buck driver configured to drive the first and second buck switching transistors at a buck duty cycle and to generate control signals for a boost driver configured to drive the first and second boost switching transistors at a boost duty cycle, the duty cycle controller comprising at least a duty cycle timer value and an offset timer value, wherein the duty cycle controller uses the duty cycle timer value and the offset timer value to establish one or more transition thresholds to control transitions between the buck, the buck-boost and the boost operation modes of the voltage converter, wherein the duty cycle timer value is indicative of a minimum on time or a minimum off time of the buck and boost switching transistors, and the offset timer value is indicative of variations and tolerance in the transistor switch time over temperature and process variations; and wherein the duty cycle controller is configured to measure the buck duty cycle and the boost duty cycle, and to digitally compare the buck duty cycle and the boost duty cycle to the one or more transition thresholds to control the transitions between the buck, the buck-boost and the boost operation modes of the voltage converter.