US Patent 7304871 Boost circuit capable of step-up ratio control

When a step-up ratio control circuit sets a step-up ratio of a charge pump circuit to 1.0 to enable a short mode, a path inside the charge pump circuit is short-circuited and a first transistor is completely turned on. This produces an inrush current derived from a battery voltage of a lithium ion battery flowing into the charge pump circuit. To address this, a constant current circuit is operated so that the first transistor is turned on slowly. Further, the operation of an oscillator and an operational amplifier is suspended when the short mode is enabled.