Design and implementation of regulated charge pump with high precision for USB-OTG application

Abstract

A regulated charge pump circuit is realized in a 3.3V 0.13-um CMOS I/O technology. The regulated charge pump exploits `Automatic Driving Buffer` scheme to generate 5V constant output voltage which is independent of load current and to lower output ripple voltage up to 40mV with 2uF load capacitor. To make stable output voltage, the regulated charge pump detects the variation of output boosted voltage which is higher than power supply voltage. As the variation of detected output voltage, 6-bit control signal is obtained and controls the `Automatic Driving Buffer` which is composed of four parallel buffers. The `Automatic Driving Buffer` operates selectively by `Driving Buffer Size Control Unit` and controls pumping current with 6-bit control signals. Therefore, by controlling of charge current as the variation of boosted output voltage, the regulated charge pump generates stable boosted output voltage. At simulation, the operation with the variation of process, voltage, temperature is checked and the performance of regulated charge pump is compared with that of conventional charge pump. Test chips demonstrate the boosted output voltage to be 5V and 30mA load current with 500KHz input clock signal. The output ripple voltage is less than 40mV with 2uF load capacitor.