Time-Based Buck Converter with Variable Frequency DCM and ON-Time Correction for Seamless Transitions

A time-based compensator represents an effective solution to overcome the limitations of the traditional voltage mode controllers, as it allows to reduce both the die area occupation and the quiescent power consumption without compromising the control loop performances. Buck converters driven by high switching frequencies suffer from relatively low efficiency in medium/light load conditions, given the large power losses associated to the switching activity. Usually, to overcome this limitation the converter is operated in pulse frequency modulation (PFM), which makes it necessary to design an additional control loop and adds a DC offset to the output voltage as well. This paper proposes a variable switching frequency time-based control, able to operate the converter both in continuous and discontinuous current mode to guarantee high efficiency for a wide load current range. In addition, seamless frequency transition are obtained with a dedicated on-time correction circuit, which keeps the average inductor current constant upon variations of the operating regime. The proposed method boosts the efficiency in medium-light load conditions, ensuring an overall efficiency above 85% over a wide load current range. The effectiveness of this technique is supported by theoretical analysis and simulation results.