Patent ID: 8890503
Filing Date: 2014-11-18
Classification: G05F

Abstract:
1. A step-down power supply circuit, comprising: first and second reference voltage source circuits configured to generate prescribed reference voltages; a first step-down voltage generation circuit, including a transistor to the source of which a first voltage is supplied, a resistor string in which a plurality of resistors are coupled in series and which is provided between the transistor and a second voltage, and an operational amplifier which controls the transistor, the first step-down voltage generation circuit generating a first step-down output voltage at a first node among a plurality of resistor-coupling nodes in the resistor string; a plurality of switches, coupled to the plurality of resistor-coupling nodes respectively; a comparison circuit configured to compare a voltage at a common node coupled in common by the plurality of switches with the output voltage of the second reference voltage source circuit, while the plurality of switches are switched; and a calibration control circuit configured to select any one among the plurality of switches according to a comparison result of the comparison circuit to perform a calibration, wherein the calibration control circuit, during a calibration operation of the first step-down voltage generation circuit, couples a second node among the plurality of resistor-coupling nodes to a non-inverting input terminal of the operational amplifier, and couples the output of the first reference voltage source circuit to an inverting input terminal of the operational amplifier; and, the calibration control circuit, after the calibration of the first step-down voltage generation circuit, couples the common node to the non-inverting input terminal of the operation amplifier, and couples the output of the second reference voltage source circuit to the inverting input terminal of the operational amplifier.