A small ripple regulated charge pump with automatic pumping control schemes

Two schemes for a charge pump are presented, to reduce output ripple voltage, with high load current drivability. The first is an automatic pumping current control scheme which automatically adjusts the size of the pumping driver to reduce the ripple voltage. The second is an automatic pumping frequency control scheme, which changes the pumping period by controlling a VCO. The prototype chip provides 30-mA load current and delivers a regulated 4.5-V output with a flying capacitor of 330-nF and a clock frequency which automatically varies from 400-kHz to 600-kHz at a 3.3-V supply. The area is 0.25 mm/sup 2/ in a 3.3-V 0.13-/spl mu/m CMOS technology, and measured output ripple voltage is less than 33.8-mV with 2-/spl mu/F load capacitor. Power efficiency is higher than 70%.