Semiconductor integrated circuit and power supply switching method

A semiconductor integrated circuit, comprising:

• a first regulator for generating a first internal power supply voltage by transforming an external power supply voltage;
• a second regulator for generating a second internal power supply voltage by transforming the external power supply voltage;
• a processor circuit configured to operate itself by being supplied with the first internal power supply voltage;
• an RTC circuit for generating a current time data by being supplied with the first internal power supply voltage and the second internal power supply voltage;
• a first supply line supplying the first internal power supply voltage to the processor circuit;
• a second supply line supplying the second internal power supply voltage to the RTC circuit;
• a changeover switch provided between the first supply line and the second supply line and switching between a connection state and a non-connection state between the first supply line and the second supply line;
• and
• a power supply level detection circuit detecting a voltage level of the external power supply voltage, and stopping operation of the first regulator and controlling the changeover switch to achieve the non-connection state between the first supply line and the second supply line if detecting that the voltage level is equal to or lower than a predetermined threshold.

A power supply switching method in a semiconductor integrated circuit, the semiconductor integrated circuit comprising:

• a regulator for generating an internal power supply voltage by transforming an external power supply voltage;
• a processor circuit configured to operate itself by being supplied with the internal power supply voltage;
• an RTC circuit for generating a current time data by being supplied with the internal power supply voltage;
• a supply line supplying the internal power supply voltage to the RTC circuit and to the processor circuit;
• and a changeover switch provided between the supply line and the processor circuit and switching between a connection state and a non-connection state between the supply line and the processor circuit, wherein the power supply switching method comprises:
• a step of detecting a voltage level of the external power supply voltage;
• and
• a step of controlling the changeover switch to achieve the non-connection state between the supply line and the processor circuit if detecting that the voltage level is equal to or lower than a predetermined threshold.