Inverting buck-boost using single-inductor boost and charge pump with a grounded switch

Abstract

The disclosed methodology for buck-boost inverted voltage conversion uses a boost stage coupled to a charge pump stage at a switch node controlled by a transistor switch coupled between the switch node and ground. The boost stage includes a boost inductor coupled between an input supply voltage and the switch node, and the charge pump stage includes a charge pump capacitor coupled between the switch node and a pump node which is coupled to the load and an output capacitor in parallel with the load. The regulated inverted output voltage is supplied to the output capacitor and the load by: (a) in a first phase, switching the transistor switch to conducting to couple the switch node to ground, and thereby (i) transferring energy from a source of input voltage source to the boost inductor, and (ii) transferring energy from a charge pump capacitor to the output node, and (b) in the second phase, switching the transistor switch to non-conducting and clamping the charge pump capacitor at a positive reference voltage, and thereby transferring energy from the boost inductor to the charge pump capacitor. In one embodiment, the positive reference voltage is the input voltage (i.e., during the second phase, the charge pump capacitor is clamped to the input voltage).