Voltage Regulation in an Integrated Controller of a Spread-Spectrum-Clocked Buck Converter

The switching converters sometimes use spread-spectrum technique to ensure the reduction of electromagnetic emissions by distributing the energy around the clock frequency and reducing its amplitude. The change of the clock frequency naturally causes the change of the output voltage if the duty cycle is not controlled properly, i.e. kept constant. This paper presents an architecture that consists of a phase-locked loop used to generate the spread-spectrum signal and a duty cycle control circuit that ensures the constant duty cycle and consequently constant out put voltage of a buck converter. These two circuits work in close co-operation to ensure smooth transition from one clock frequency to the next in order to keep the duty cycle as constant as possible. The operation of the controller circuit is explained as well as the function of each block in the controller. The operation of the phase-locked loop is presented together with several compensation techniques used to reduce the change of the duty cycle when the clock frequency is changed. An optimal set of parameters for the exponential optimization is found.