A High-Frequency Three-Level Buck Converter With Real-Time Calibration and Wide Output Range for Fast-DVS

This paper presents a 50-MHz 5-V-input 3-Woutput three-level buck converter. A real-time flying capacitor (CF) calibration is proposed to ensure a constant voltage of Vg/2 across CF, which is highly dependent on various practical conditions, such as parasitic capacitance, time mismatches, or any loading circuits from CF. The calibration is essential to ensure the reliability and minimize the inductor current and output voltage ripple, thus maintaining the advantages of the three-level operation and further extending the system bandwidth without encountering sub-harmonic oscillation. The converter is fabricated in a UMC 65-nm process using standard 2.5-V I/O devices, and is able to handle a 5-V input voltage and provide a 0.6-4.2-V-wide output range. In the measurement, the voltage across CFis always calibrated to Vg/2 under various conditions to release the voltage stress on the highand low-side power transistors and CF, and to ensure reliability with up to 69% output voltage ripple reduction. A 90% peak efficiency and a 23-29-ns/V reference-tracking response are also observed.