Charge pump circuits having a fractional negative voltage output from a positive voltage input. A control circuit provides for feedback control of the output of such a charge pump, and may include dynamic adjustment of the charge pump output based on one or more factors. In some embodiments, two or more charge pumps are coupled in a differential configuration such that while one set of capacitors are in series charging, at least one other set of capacitors is discharging. One embodiment encompasses a fractional negative voltage charge pump including n≥2 capacitors configured to be coupled in series between an input voltage and ground during a charging phase, and in parallel between ground and an output terminal during a discharging phase. The fractional negative voltage charge pump outputs a negative voltage that is no more than 1/n of a positive voltage input in magnitude.