Constant On-Time Multi-Mode Digital Control with Superior Performance and Programmable Frequency

The need for smaller size and extended battery life in portable devices poses a tough challenge to design multi-mode digital control in DC-DC converters while operating over a wide range of load current and input voltage. This paper presents a multi-mode digital controller which shares a common constant on-time modulator and achieves high efficiency, fast transient response, smooth transitions, and programmable switching frequency by dynamically adjusting the on-time with the input voltage during light load conditions to keep the voltage ripple within the desired band. The digital modulator uses the event-based sampling for voltage-loop which achieves inherent current-loop stability. The proposed scheme offers a natural transition to DCM. Further, the stability analysis using discrete-time model and design of the proposed scheme are discussed. Both the buck and boost converter prototypes are made, and the proposed scheme is implemented using an FPGA device.