A system includes a voltage controlled oscillator, a charge pump, and a current regulator circuit. The voltage controlled oscillator has a control input and a clock output that provides a clock signal at a clock frequency that is variable. The charge pump is coupled to the clock output and has an output that provides a boosted output voltage. The current regulator circuit is coupled to the control input of the voltage controlled oscillator to adjust the clock frequency based on a simulation of a rate of change of the boosted output voltage. This allows for a controlled slew rate for the output of the charge pump.