Digital control techniques for DC-DC synchronous Buck converters

This thesis studies digital control techniques for DC-DC synchronous Buck converters. In switched-mode DC-DC converters, digital control can have significant benefits over traditional analog control schemes. These benefits include programmability, smart power management and simpler system interfaces. Furthermore, integration of high-performance digital controllers may take advantages of advanced digital process technologies to decrease the size and cost of the power management system. Techniques presented in this thesis are aimed at further improvements in practical digital control for step-down DC-DC applications.;A dual mode digital controller structure for synchronous buck converters is presented to improve the light-load efficiency. The controller includes automatic mode switching and input voltage feed forward which improves the performance over a wide range of input voltages. The controller parameters, such as the PWM (pulse-width modulation) switching frequency, PFM (pulse frequency modulation) pulse on time, and PWM/PFM mode transition points, are programmable.;Two controller structures are evaluated and compared for multiphase buck converters: a central controller and a distributed controller. A sensorless current sharing method is proposed for the central controller structure. The origins of the current imbalance among phases are analyzed. The corresponding system mismatches are estimated and compensated to achieve current sharing without current sensing. A single wire serial communication protocol is proposed and implemented for the distributed controller structure. Both voltage error and current information are transmitted through the single wire digital bus among phases to achieve voltage regulation and current sharing. A small signal model is developed for design of voltage regulation and current sharing loops, taking into account the communication delays.;Experimental verifications are included for digitally controlled single phase and multiphase buck converters. The digital controllers are implemented on an FPGA platform. Significant improvements in efficiency, systemic simplicity, and modularity are demonstrated.