LAUSR

It is essential to retain improved efficiency in a dc–dc converter over a wide load current range to extend the battery-life in portable devices. This requires a multi-mode controller, consisting of pulse-width-modulation (PWM) and pulse-frequency-modulation (PFM) schemes. However, existing approaches attempt to integrate structurally different controllers; thus it is difficult to achieve a seamless controller transition. While a digital platform offers controller configurations, it remains difficult to identify a suitable digital PWM/PFM technique and decide on its sampling mechanism to achieve stable behavior. This paper proposes a unified digital PWM/PFM scheme which shares a common digital PWM (DPWM) block and has the provisions for online controller configuration and automatic (switching) frequency adaptation. The proposed scheme retains improved efficiency over a wide operating range and inherently achieves seamless controller transitions. Further, a unified discrete-time framework is proposed for the analysis and design of the proposed multi-mode controller. Buck and boost converter prototypes are tested and the proposed controller is implemented using a field-programmable-gate-array device.