A 94.8% Peak-Efficiency 3-Level Buck Converter with Fast Flying Capacitor Charging Technique

This paper presents a 3-Level Buck Converter (3LBC) with a Fast-Flying Capacitor Charging (FFCC) technique. Unlike previous Flying Capacitor voltage (VCF) calibration methods, FFCC allows VCF to track input voltage (VIN) changes even without switching events. This continuous calibration keeps VCF close to VIN/2 and eliminates over-voltage stress during sudden VIN shifts. Additionally, FFCC enables faster calibration compared to previous methods, which were limited by the loop bandwidth due to stability concerns. FFCC, using only a comparator, achieves higher speed without stability issues. Experimental results show that with FFCC enabled, VCF stabilizes within 10µsec when VIN changes from 2.8V to 5V, compared to 3msec without FFCC. The steady-state VCF deviation remains within 1.7% of VIN/2, demonstrating FFCC's effectiveness under both transient and steady-state conditions. The proposed 3LBC achieves over 85% efficiency across a 1mA to 500mA load range, with a peak efficiency of 94.8%. The chip, fabricated in a 180nm CMOS process, occupies an area of 2.7mm x 1.7mm.