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The paper introduces a high output current and high switching frequency buck DC-DC regulator with gate scaling function to improve the efficiency at light load together with reduced output voltage ripple and noise. External FET driver is also implemented as an option to move the excessive heat from inside the chip for thermal sensitive applications. A fast current sensing loop method is used to minimize the limitation of minimum on time of the conventional current mode buck converter. A guardring strategy for power MOSFET to prevent the latch up and minority carrier injection is also discussed. It is fabricated in TSMC 0.35 um CMOS process with dual-poly and quad-metal. The WLCSP (Wafer Level Chip Scale Package) is used to minimize the parasitic, as well as to reduce the board size in application. The measurement result reaches nearly 85% efficiency at 2A load current when input voltage is 3.6V and output voltage is 1.1V.