Semiconductor integrated circuit and operating method thereof

Abstract

A semiconductor integrated circuit included a power supply circuit having a first input terminal, a second input terminal, and an output terminal, wherein the power supply circuit includes a measurement circuit and a switch circuit, wherein the measurement circuit compares a first voltage supplied to the first input terminal with a second voltage supplied to the second input terminal, outputs a determination signal as the comparing result and operates on the first voltage, wherein the switch circuit selects the first input terminal or the second input terminal and couples the selected terminal with the output terminal in response to the determination signal, wherein a main power supply voltage from a main power supply can be supplied to the first input terminal, and wherein an auxiliary power supply voltage from an auxiliary power supply can be supplied to the second input terminal.

What is claimed is: 
     
         1 . A semiconductor integrated circuit comprising:
 a power supply circuit having a first input terminal, a second input terminal, and an output terminal,   wherein the power supply circuit includes a measurement circuit and a switch circuit,   wherein the measurement circuit compares a first voltage supplied to the first input terminal with a second voltage supplied to the second input terminal, outputs a determination signal as the comparing result and operates on the first voltage,   wherein the switch circuit selects the first input terminal or the second input terminal and couples the selected terminal with the output terminal in response to the determination signal,   wherein a main power supply voltage from a main power supply can be supplied to the first input terminal,   wherein an auxiliary power supply voltage from an auxiliary power supply can be supplied to the second input terminal, and   wherein the output power supply voltage can be supplied to a load.   
     
     
         2 . The semiconductor integrated circuit according to  claim 1 ,
 wherein, when the main power supply voltage supplied to the first input terminal is higher than the auxiliary power supply voltage supplied to the second input terminal, control is made in response to the determination signal of the measurement circuit so that the switch circuit selects the first input terminal to be coupled with the output terminal and   wherein, when the main power supply voltage supplied to the first input terminal is lower than the auxiliary power supply voltage supplied to the second input terminal, control is made in response to the determination signal of the measurement circuit so that the switch circuit selects the second input terminal to be coupled with the output terminal.   
     
     
         3 . The semiconductor integrated circuit according to  claim 2 ,
 the power supply circuit having a switch control circuit,   wherein the switch control circuit controls the switch circuit in response to the determination signal of the measurement circuit and operates on the output power supply voltage.   
     
     
         4 . The semiconductor integrated circuit according to  claim 3 ,
 wherein the measurement circuit includes a comparator that operates on the main power supply voltage supplied to the first input terminal and compares the main power supply voltage supplied to the first input terminal with the auxiliary power supply voltage supplied to the second input terminal, and   wherein the determination signal of the measurement circuit is generated from an output terminal of the comparator.   
     
     
         5 . The semiconductor integrated circuit according to  claim 1 ,
 wherein the switch circuit includes a first switch element coupled between the first input terminal and the output terminal and a second switch element coupled between the second input terminal and the output terminal.   
     
     
         6 . The semiconductor integrated circuit according to  claim 5 ,
 wherein the first switch element, which is coupled between the first input terminal and the output terminal and included in the switch circuit, has such a configuration as to prevent a backflow from the output terminal to the first input terminal, and   wherein the second switch element, which is coupled between the second input terminal and the output terminal and included in the switch circuit, has such a configuration as to prevent a backflow from the output terminal to the second input terminal.