This paper proposes a hybrid DC-DC converter with a new power switch structure and its operating principles. Its main application is a power management IC that supplies compact mobile devices with a low-profile chip inductor, whose DC resistance is relatively high. In step-down mode, DC current flowing through the inductor is reduced by introducing a flying capacitor that assists load current at a certain phase. In step-up mode, average inductor current is smaller than the load current because of power-input power-output equation. A three-phase mode is also added to fill output voltage gap between step-up and step-down modes. By reducing inductor conduction loss, this work shows better power conversion efficiency than a conventional buck converter at heavy load. Using 180 nm general purpose process, the proposed converter takes 2.5 V input and supplies output in between 1.4 V and 5 V. Load current ranges in between 0.3 A and 1.5 A with peak power conversion efficiency of 92.87%.