Power supply monitoring circuit

A power supply monitoring circuit configured to monitor an in-vehicle power supply in an electronic control unit having a plurality of built-in power supply circuits, the plurality of built-in power supply circuits being configured to be powered by the in-vehicle power supply through a power supply line to generate and supply power to a downstream load, the power supply line being commonly connected to the plurality of built-in power supply circuits and the in-vehicle power supply, the power supply line having a branching node at which the power supply line is branched out from the in-vehicle power supply to the plurality of built-in power supply circuits, the power supply monitoring circuit comprising:

• a voltage monitoring circuit configured to monitor the in-vehicle power supply by monitoring the power supply line;
• and
• a control circuit configured to
• start up in response to a voltage of the in-vehicle power supply crossing a predetermined reset voltage and control the plurality of built-in power supply circuits or a device powered by the plurality of built-in power supply circuits to discharge an operational charge remained in the plurality of built-in power supply circuits or the device, and
• control the plurality of built-in power supply circuits to start up based on a condition that
• an output voltage of the plurality of built-in power supply circuits drops to a voltage level that does not cause an unstable operation of the downstream load, and
• the voltage of the in-vehicle power supply exceeds a predetermined start-up voltage.