Digitally controlled multi-phase buck-converter with merged capacitive attenuator

This paper introduces a new topology that combines a capacitive divider and an interleaved buck to reduce the volume of multi-phase step-down converters. The size reduction is obtained with a low penalty in conduction losses, input filter size, and controller complexity. At heavy loads, the converter efficiency is comparable to that of a conventional buck and at light to medium loads it is improved. The volume reduction is obtained by utilizing the inductors of the buck stage to regulate the tap voltages of the capacitive divider. This eliminates a bulky energy transfer capacitor existing in other switch capacitor (SC) circuits, reduces the number of switches in the conduction path, and simplifies control of the converter. Experimental results obtained with a 7V-to-1V, 10A, 1 MHz prototype demonstrate that the merged capacitor converter has 15% smaller inductor, 13% reduction in output capacitor value and up to 35% reduction in power losses, and 15% faster transient response than a time-optimal controlled buck.