SEMICONDUCTOR INTEGRATED CIRCUIT DEVICE AND SWITCH INPUT CIRCUIT

PROBLEM TO BE SOLVED: To constitute a switch input circuit by using an extremely small number of externally-added parts, and to adopt a low pressure resistance process. SOLUTION: When an ignition switch 3 is turned on, an electric current ID1 flows from a battery 2 to an MOSFET 33 through a resistor 23 and in response thereto, an electric current ID2 also flows through an MOSFET 34. A voltage Vin appearing at an input terminal 22a is limited to a gate-source voltage VGS of the MOSFET 33. When a drain voltage VD2 of the MOSFET 34 is lower than a lower level threshold Vn of a Schmitt inverter 36, a detection signal SIG is changed into an H level so that a switch input circuit 26 detects that the ignition switch 3 is turned on. COPYRIGHT: (C)2008,JPO&INPIT