Analysis and Design of a Digital Average Current-mode Controlled Buck Converter

Digital average current-mode control (CMC) technique is popular in the power management industry due to its better noise immunity and the ability to track average current with high accuracy. A discrete-time framework for modeling and analysis of the inner current-loop of a digital average current-mode controlled buck converter is presented in this paper. A discrete-time 1-D model of the current loop is exploited for both fast-scale stability analysis and controller tuning of the inner current loop. The analysis shows that stable range of the proportional gain of the current loop PI controller is limited by the applied input voltage of the buck converter. An analytical expression of the stable range of proportional gain is derived from the proposed analysis. A buck converter prototype is developed and digital controllers are implemented in a 32-bit microcontroller (TMS320F28335 from Texas Instruments). Experimental results show a good agreement with the proposed analysis. The framework of this paper can be exploited to analyze the stability status of average CMC in other types of DC-DC converters.