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A fully integrated dc-dc four-phase step-down converter in a 130-nm 1.2-V CMOS technology is realized with integrated metal-track inductors and integrated MOS and MIM capacitors. The converter requires no external components and is designed to generate an output voltage of 1.2 V out of a 2.6 V supply voltage. The maximum power-conversion efficiency is 58%, for a voltage-conversion ratio of 0.46. This yields a 21% improvement over a linear converter. The maximum output power is 800 mW and the power density of 213 mW/mm2 is in the same order of magnitude of nonintegrated switching converters, even when not taking their off-chip output filter into account. Stacked transistors are used to cope with the high voltage. A novel control system based on semiconstant ON/OFF time (SCOOT) regulates the output voltage. It also provides stability over the entire load range from 0 to 800 mW. The four-phase topology and the SCOOT control system ensure an output voltage ripple below 10% of the output voltage. The converter operates in discontinuous, synchronous switching mode. The switching frequency varies with the load from 75 kHz to 225 MHz.
Date of Publication: Feb. 2011