Patent ID: 7592856
Filing Date: 2009-09-22
Classification: H02M,H05B,Y02B

Abstract:
1. A driver circuit for a charge pump circuit capable of switching between a plurality of step-up ratios, including 1 and a value higher than 1, comprising: a control unit which controls the charge pump circuit; a first oscillator which outputs a first periodic signal; and a second oscillator which outputs a second periodic signal employed for a time measurement for setting the step-up ratio and having a frequency set lower than that of the first periodic signal, and wherein, when the step-up ratio of the charge pump circuit is larger than 1, the control unit turns on only the first oscillator to perform, based on the first periodic signal, a time measurement for setting the step-up ratio and the control of a step-up action of the charge pump circuit, and wherein, when the step-up ratio of the charge pump circuit is 1, the control unit turns on only the second oscillator to perform the time measurement for setting the step-up ratio based on the second periodic signal; wherein the control unit switches the step-up ratio of the charge pump circuit when the voltage to be monitored for switching the step-up ratio of the charge pump circuit satisfies a predetermined condition for a period of time equal to or longer than a predetermined period of time, and the control unit performs the time measurement for setting the step-up ratio at this time based on the first or second periodic signal; and wherein the frequency of the second periodic signal is set higher than a minimum frequency required for measuring the predetermined period of time in the control unit.