Abstract: The present invention utilizes a plurality of transistors configured such that the drain/well diode of the PMOS switch is not forward biased during any part of the charge pump cycle. In one embodiment a plurality of transistors are coupled between the drain, source and well of the PMOS switch such that the well of the PMOS switch is connected to a voltage that is one base-emitter voltage drop (Vbe) less than the higher of either the source voltage or the drain voltage. Since the well is always a single Vbe below the higher of the source voltage or the drain voltage, the gate-well diodes of the PMOS switches are prevented from becoming forward biased, thereby reducing current drain and resulting in improved efficiency of the charge pump.

Abstract: The presently disclosed method and apparatus provides the sensing of an output voltage of a charge pump without applying a load to the output stage. In the charge pump the voltage change which occurs across a capacitor of a stage of the charge pump when the charge pump transfers charge to the next stage is proportional to the difference between the voltage at the output of the charge pump under load, and the voltage which will be developed at the output of the charge pump with no load. There is an interval in the timing of the charge pump cycle after the first stage capacitor has transferred its charge to a second stage capacitor where the high side of the first capacitor has not yet been connected to the line voltage. During this interval the charge pump undervoltage detection circuit measures the voltage at the high side of the capacitor and compares this measured voltage to a reference voltage.