Patent ID: 8664798

Claim:
A semiconductor integrated circuit device including an external power supply terminal, a power supply circuit for generating an internal supply voltage from an external supply voltage supplied to the external power supply terminal, and a first functional circuit for receiving the internal supply voltage and carrying out a prescribed circuit function, wherein the power supply circuit comprises: a step-down converter for receiving the external supply voltage and generating a first stepped-down voltage lower than the external supply voltage; a control circuit for comparing the external supply voltage with a reference voltage to provide a control signal indicative of the comparison; and a switch for selecting one of the external supply voltage and the first stepped-down voltage according to the control signal, and supplying the selected voltage as the internal supply voltage to the first functional circuit, wherein the switch comprises: a transistor for receiving the first step-down voltage and outputting the first stepped-down voltage to the first functional circuit responsive to the control signal when the external supply voltage is higher than the reference voltage, and another transistor for receiving the external supply voltage and outputting the external supply voltage to the first functional circuit responsive to the control signal when the external supply voltage is lower than the reference voltage.