High-speed flying capacitor voltage calibration and seamless mode transition technique for three-level DC-DC boost converter

Abstract

This thesis introduces a fully state-based phase selection (FSPS) technique for a current-mode three- level boost converter (3L-BST). The proposed FSPS technique dynamically selects the operating phase of the 3L-BST to ensure that the voltage across the flying capacitor (VCF) is maintained at half of the output voltage (VO) and changes the operation mode at the mode transition region. It enables a seamless transition of the operation mode and consecutive charging or discharging of the flying capacitor at the same duty cycle during each switching period. Hence, the 3L-BST enhances the speed of VCF calibration while ensuring a stable startup, eliminating sub-harmonic oscillations in the inductor current resulting from VCF calibration. Additionally, this leads to a reduction in output voltage fluctuations within the mode transition region. Moreover, for the stability of both valley and peak current-mode control across a wide output voltage range, the presented FSPS technique uses an adaptive slope generator (ASG) with an adjustable slope that can seamlessly transition from negative to positive. The implemented 3L-BST with FSPS technique, fabricated in a 0.18-μm bipolar-CMOS-DMOS (BCD) process, occupies a chip area of 5.51 mm². The proposed 3L-BST achieves a peak efficiency of 95.3%, accommodating an input range of 2–6 V, an output range of 5–32 V, and supporting a maximum load current of 0.5 A. Notably, the inductor current ripples are reduced by a factor of 1.45 compared to previous VCF calibration methods and the entire startup time takes 490 μs.