MaxLinear's PowerXR series is another approach. This is a multi-channel multi-rail digital controller family which allows software control of the major attributes of the multi-rail power system. The parts count is minimal, requiring just the addition of the MOSFETs of your choice and the desired inductor to match the necessary characteristics of each channel. Multiple rails are available in three or four channel increments. Daisy chaining of the I²C channels allows from three to twenty or more channels with one interface controlling all the channels. This makes easy expansion to as many channels as necessary possible.