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-W-output three-level buck converter. A real-time flying capacitor ( $C_{F}$ ) calibration is proposed to ensure a constant voltage of $V_{g}$ /2 across $C_{F}$ , which is highly dependent on various practical conditions, such as parasitic capacitance, time mismatches, or any loading circuits from $C_{F}$ . 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 $C_{F}$ is always calibrated to $V_{g}$ /2 under various conditions to release the voltage stress on the high- and low-side power transistors and $C_{F}$ , 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.