1. A circuit comprising: a first multi-stage charge pump circuit comprising a plurality of series-connected directional pump stages, each respective stage configured to transfer charge from a respective input thereof to a respective output thereof; said first multi-stage charge pump circuit selectable to develop a positive voltage on an output node of the first charge pump circuit for a first mode of operation, and selectable to develop a negative voltage on another output node of the first charge pump circuit for a second mode of operation; and a second multi-stage charge pump circuit, coupled in cooperation with the first multi-stage charge pump circuit to generate a single output voltage at times, and decoupled to operate independently so that the first and second charge pump circuits generate separate output voltages at other times.