Integrated circuit, associated start-up circuit and start-up method thereof

A start-up method for an integrated circuit, the method comprising:

• coupling a normally-on switching device and a normally-off switching device in series, wherein the normally-on switching device has a first terminal, a second terminal, and a control terminal, the normally-off switching device has a first terminal, a second terminal, and a control terminal, the first terminal of the normally-off switching device is coupled to the second terminal of the normally-on switching device;
• receiving an enable signal, wherein the enable signal is configured to control the integrated circuit to be initiated or to be shut down;
• comparing the enable signal with a reference signal;
• and
• charging a power supply capacitor during start-up of the integrated circuit;
• wherein
• when the enable signal is less than the reference signal, activating a first path and charging the power supply capacitor by an input voltage via the normally-on switching device and the first path;
• and wherein
• when the enable signal is larger than the reference signal, activating a second path and charging the power supply capacitor by the input voltage via the normally-on switching device and the second path.

A start-up circuit used in an integrated circuit for a switching power supply circuit with a normally-on switching device and a normally-off switching device coupled in series, the start-up circuit comprising:

• a current path configured to be coupled between a power supply pin of the integrated circuit and a connection node of the normally-on switching device and the normally-off switching device, wherein the power supply pin is configured to be coupled to a power supply capacitor;
• and
• a comparator configured to compare a voltage across the power supply capacitor with a first reference threshold;
• wherein when an enable signal received at an enable pin of the integrated circuit is less than a reference signal, the current path provides a first charge current to the power supply capacitor;
• and wherein
• when the enable signal is larger than the reference signal, the current path provides a second charge current to the power supply capacitor, wherein the second charge current is higher than the first charge current, and the enable signal is configured to control the integrated circuit to be initiated or to be shut down.