Patent ID: 6787936
Filing Date: 2004-09-07
Classification: G06F,H02J

Abstract:
A semiconductor integrated circuit comprising:a micro-controller havina at least two electronic circuits; a power supervisory circuit for supervising power supply voltage of an externally located main power source and a backup power source; a first power supply terminal connected to the main power source; a second power supply terminal connected to the backup power source; a first power supply line connecting a first electronic circuit of said micro-controller and said first power supply terminal; and a second power supply line connecting a second electronic circuit of said micro-controller and said second power supply terminal, wherein said power supervisory circuit is supplied with main power from the main power source through said first power supply terminal, and supplied with backup power from the backup power source through said second power supply terminal, and said power supervisory circuit includes a first switch connecting said first and second power supply terminals to each other and disconnecting said first and second power supply terminals from each other; and a control circuit which monitors the main power source and controls said first switch, wherein, when the main power source is normal, said control circuit controls said first switch so that the first and second electronic circuits are driven by power from the main power source, and when the main power source has a failure, said control circuit controls said first switch so that the second electronic circuit is driven by power from the backup power source, and said control circuit monitors a difference between voltages at said first and second power supply terminals, and determines that the main power source has a failure when the difference is larger than a threshold value.