Step-up dc-dc converter and semiconductor integrated circuit device

A semiconductor integrated circuit device comprising:

• a signal input terminal;
• a signal output terminal;
• a battery power supply input terminal;
• a direct-current voltage input terminal;
• a semiconductor switching element control output terminal;
• a control logic that generates a drive voltage to be provided to the semiconductor switching element;
• a power supply circuit that receives a battery voltage via the battery power supply input terminal and boosts and outputs the received battery voltage;
• a buffer that receives the drive voltage generated and outputted by the control logic, receives the voltage outputted by the power supply circuit as a power supply, level-shifts the received drive voltage using the received power supply, and provides the level-shifted drive voltage to the semiconductor switching element via the semiconductor switching element control output terminal;
• a voltage detection circuit that receives and detects the battery voltage;
• an oscillator circuit that changes the oscillation frequency on the basis of the voltage detected by the voltage detection circuit;
• and
• a load element that has an input thereof connected to the signal input terminal and an output thereof connected to the signal output terminal, receives the battery voltage via the battery power supply input terminal, receives a voltage generated by the semiconductor switching element via the direct-current voltage input terminal, and operates using both the received voltages as power supplies,
• wherein the signal input terminal, the signal output terminal, the battery power supply input terminal, the direct-current voltage input terminal, the semiconductor switching element control output terminal, the semiconductor switching element, the control logic, the power supply circuit, the buffer, the voltage detection circuit, the oscillator circuit, and the load element are integrally formed on a common semiconductor substrate.