A controller for controlling a plurality of DC-DC switching cells each configured to generate an output voltage in response to receiving a PWM control signal from the controller. The controller includes a plurality of output ports for outputting a plurality of PWM control signals, and at least one input port for receiving a plurality of output voltages from the plurality of switching cells. The controller is configured to sample the plurality of output voltages one at a time via a multiplexer and to regulate the output voltages in response to the sampling.