DSP-Based Control of Multi-Rail DC-DC Converter Systems with Non-Integer Switching Frequency Ratios

Abstract

This paper examines the use of non-integer switchingfrequency ratios in digitally controlled DC-DC converters. Inparticular the execution of multiple control algorithms using aDigital Signal Processor (DSP) for this application is analyzed.The variation in delay from when the Analog to DigitalConverter (ADC) samples the output voltage to when the dutycycle is updated is identified as a critical factor to be consideredwhen implementing the digital control system. Fixing the delayto its maximum value is found to produce reasonableperformance using a conventional DSP. A modification of theDSP’s interrupt control logic is proposed here that minimizesthe delay and thereby yields improved performance comparedwith that given by a standard interrupt controller. Applying thistechnique to a multi-rail power supply system provides thedesigner with the flexibility to choose arbitrary switchingfrequencies for individual converters, thereby allowingoptimization of the efficiency and performance of the individualconverters.