Semiconductor device to select a power supply

Abstract

A power supply selection/detection circuit to select one main power supply from a plurality of external power supplies includes a resistance element with one end connected to an external power supply and another end connected to the main power supply, a first voltage detector to receive a voltage of the external power supply and detect a voltage of the external power supply, a second voltage detector to detect a voltage between the ends of the resistance element, and a switch connected between the external power supply and a ground to short-circuit or open-circuit between the external power supply and the ground according to an output of the second voltage detector. The resistance element and the first voltage detector are disposed for each of the plurality of external power supplies, and the second voltage detector and the switch are disposed for at least one of the plurality of external power supplies.

1 . A semiconductor device to select a power supply providing a voltage from first and second external power supplies, comprising:
 a first node that receives a first voltage from said first external power supply;   a second node that receives a second voltage from said second external power supply;   a third node that receives a third voltage;   a fourth node that receives said third voltage;   an output node coupled to said first node or said second node;   a first switch, a one end of said first switch coupled between said first node and said output node;   a second switch, a one end of said second switch coupled between said second node and said output node;   a first path coupled between said third node and said output node through said first switch; and   a second path coupled between said fourth node and said output node through said second switch,   wherein a control node of said first switch is not connected to said second path.   
     
     
         2 . The semiconductor device according to  claim 1 , further comprising a switch control circuit that controls said first and second switches,
 wherein said first and second switch are controlled by an output voltage of said switch control circuit when said first external power supply or said second external power supply provides a voltage to said output node, complementarily.   
     
     
         3 . The semiconductor device according to  claim 2 ,
 wherein said first switch is turned off when said output voltage indicates that said second external power supply provides a voltage to said output node, and   wherein said second switch is turned off when said output voltage indicates that said first external power supply provides a voltage to said output node.   
     
     
         4 . The semiconductor device according to  claim 3 ,
 wherein said second power supply is a USB (Universal Serial Bus) interface connector, and   wherein a voltage from said first external power supply is larger than a voltage from said second external power supply.   
     
     
         5 . The semiconductor device according to  claim 4 , further comprising:
 a first voltage detector coupled to said first node through said first switch to detect a voltage from said first external power supply; and   a second voltage detector coupled to said second node through said second switch to detect a voltage from said second external power supply.   
     
     
         6 . The semiconductor device according to  claim 5 ,
 wherein said second voltage detector includes first and second voltage-dividing resistors between said second switch and a ground,   
     
     
         7 . The semiconductor device according to  claim 6 ,
 wherein V/Imax>=(R 1 +R 2 ) is satisfied where a current limit is Imax, a voltage from said second external power supply is V, resistance of said first voltage-dividing resistor is R 1 , and resistance of said second voltage-dividing resistor is R 2 .   
     
     
         8 . The semiconductor device according to  claim 7 , wherein
 when a current limit of the USB interface connector in suspend mode is 500 μA and a supply voltage of the USB interface connect is 4.3 to 5.4 V, a total of the resistance of the first and second voltage-dividing resistors is 8.6 KΩ or higher.   
     
     
         9 . The semiconductor device according to  claim 8 ,
 wherein said switch control circuit includes first and second detector, and   wherein the semiconductor device further comprises:
 a first resistance element coupled between said first node and said output node; and 
 a second resistance element coupled between said second node and said output node, 
   wherein said first detector detects a voltage between both ends of said first resistance element to control said first switch, and   wherein said second detector detects a voltage between both ends of said second resistance element to control said second switch.   
     
     
         10 . The semiconductor device according to  claim 9 ,
 wherein said first and second resistance elements is one of a Schottky diode, a resistor and a transistor.