Patent ID: 7757104

Claim:
An integrated circuit comprising a source voltage monitoring unit that monitors a level of a first source voltage supplied from an external power source, determines whether the first source voltage is supplied from the external power source, and controls application of an internal power source and the external power source, wherein the source voltage monitoring unit controls so as to apply the first source voltage when determining that the first source voltage is supplied, and so as to apply a second source voltage supplied from the internal power source, whose level is lower than that of the first source voltage, when determining that the first source voltage is not supplied, and the integrated circuit operates with application of either one of the first source voltage and the second source voltage, the source voltage monitoring unit including a binarizing processing unit that outputs a binarized signal at either a High level or a Low level by comparing the level of a voltage at a terminal to which the first source voltage is applied with a predetermined reference level, and a determining processing unit that generates a selecting signal for selecting either the first source voltage or the second source voltage when the binarized signal output from the binarizing processing unit has continued at either the high level or the low level for a predetermined time.