This paper proposes a compact size DC-DC buck converter toward on-chip inductors and minimized external components. Multi-phase, high switching frequency and pseudo continuous conduction mode (PCCM) techniques  achieve the possibility to implement on-chip inductors. The effective inductance is about 20nH. Due to high switching frequency above 20MHz, it is a challenge to have a highly accurate current sense for high performance of converters. Simulation results demonstrate that the accuracy of high-speed current sensor is about 95%. Besides, mode switch between pulse width modulation (PWM) and pulse frequency modulation (PFM) alleviates the limitation of high-speed current sensor in case of light load condition. Compact size design of converter is an advanced technique as a power module for system-on-chip (SOC) designs.