| 摘要 |
PURPOSE:To realize an internal power supply voltage changeover circuit with excellent noise immunity and not malfunctioned even at application of power. CONSTITUTION:A power supply voltage changeover circuit 3 consists of a P- channel MOS transistor(TR) 16 whose gate receives an output of an inverter 15 receiving a power supply voltage switching signal 4 at its input and whose source connects to an external power supply. Moreover, a switching signal setting circuit 5 is made up of a capacitor 11 provided between an output of an external power supply voltage detection circuit 101 and an external power supply voltage, a capacitor 14 provided between a ground level power supply and an output of an inverter 12 receiving an output of the external power supply voltage detection circuit 101 at its input, and a P-channel MOS TR 13 whose drain connects to an output of the inverter 12 and whose source and gate are connected to the external power supply, and a power supply voltage switching signal 4 is set so that an output of a power supply voltage changeover circuit 3 reaches a level of an internal power supply 2. |
