Digital Controller for Multi-Phase DC-DC Converters with Logarithmic Current Sharing

This paper describes a novel current-program mode digital controller and a multiphase dc-dc converter with non-uniform current sharing that optimize converter efficiency over the full range of operation. The converter phases are operated as binary-weighted constant current sources, i.e. scaled in a binary-logarithmic fashion. To minimize the system size and provide fast dynamic response, the phases switch at different frequencies and their components are selected so that the most efficient operating points correspond to the set currents. The digital controller operates on a modification of the "phase dropping" principle. Depending on the output load, the number of active phases is dynamically changed. The new architecture of the controller does not require an analog-to-digital converter for current measurement and is suitable for high-frequency low-power converters. An experimental 4-phase buck converter utilizing the digital control architecture with logarithmic current sharing was built. A comparison of the efficiency with an equivalent uniform current shared converter shows that, at medium and light loads, the presented system results in the efficiency improvements of up to 6% and 25%, respectively.