Digital current mode control of DC-DC converters

Digital current mode control of DC-DC converters combines advantages of current mode control, including overload current protection and robust dynamics, and advantages of digital implementation, such as programmability, flexibility, and scalability. To make digital current mode control practical, this thesis attempts to address several issues: quantization and limit cycling, current sensing and resolution of current analog-to-digital (A/D) converters, digital current mode control algorithms, and implementation of overload current protection. In the study of quantization and limit cycling issues, we derive static and dynamic system models with quantizers, which help understanding of how to avoid undesirable oscillations known as limit cycling. A digital current mode control architecture and a control method are introduced to enable system realization using low-resolution current sensing. For current sensing, we propose a differential delay-line AID converter. A prototype 4-bit A/D converter chip is implemented and the performance is experimentally verified. The experimental circuit includes a DC-DC buck converter, the A/D converter, and an FPGA-based digital controller. Overload current protection for both digital current mode and digital voltage mode control method is discussed.