Patent ID: 7479767

Claim:
A power supply step-down circuit adapted to a semiconductor integrated circuit having a first operation mode and a second operation mode having a smaller current consumption than the first operation mode, comprising: a first step-down circuit, activated only during the first operation mode, and configured to step down an input power supply voltage to an output voltage; a second step-down circuit, provided integrally with the first step-down circuit and activated only during the second operation mode, and configured to step down the input power supply voltage to an output voltage; an output terminal configured to output the output voltage of one of the first and second step-down circuits that is activated, said first step-down circuit having a lower resistance, higher reaction speed and a larger current consumption compared to the second step-down circuit; and an output circuit configured to maintain the output voltage that is output from the output terminal lower than the input power supply voltage for a first predetermined time when an operation mode makes a transition from the first operation mode to the second operation mode, so that the output voltage that is output from the output terminal does not become the same potential as the input power supply voltage for a second predetermined time or longer.