Battery operation in mobile applications needs power efficient DC-DC converters which are able to handle battery voltages up to 5.5V. Normally, these DC-DC converters are built in special technologies. For decreased footprint and chip count of the overall system, a system-on-chip solution on modern CMOS technology with core supply voltages around 1V is preferred. The presented DC-DC buck converter generates 0.9 to 1.8V at output currents up to 500mA from a battery voltage of 2.4 to 5.5V with high efficiency in a high-k 28nm metal-gate CMOS technology.