Voltage Doubler/Tripler Current-Mode Charge Pump Topology with simple "Gear Box"

DC to DC converters which are realized as a switched capacitor type are very common in display and lighting low power solutions. This applications requires a lot of different supply voltage rails with different demand on the output power. E.g. a thin-film-transistor (TFT) LCD panel requires 24V - 35V at 10mA - 50mA to switch pixel transistors. A current-mode regulated charge pump generates this rail from a 12V -18V input supply. The selected charge pump topology uses a simple "gear box" controlled by a single feedback amplifier to select between doubler and tripler modes of operation. This feedback amplifier simultaneously regulates output voltage and selects the operating mode. The new topology allows less circuit complexity compare to common "gear box" solutions. Therefore this converter system with flexible conversion ratios to support different V_IN/V_OUT ratios and load currents is the ideal solution to be most efficient. Also the advantages of current-mode control where one transistor in the output stage operates as a regulated current source on the low voltage rail which can theoretically support any power stage topology will be demonstrated. The proposed charge pump is realized in a BICMOS process with HV extension. Finally the measurement results especially regarding mode transitions will be shown.