Power management circuit and method thereof

A power management circuit, adapted for a portable electronic device having a universal series bus (USB) charging port, the portable electronic device electrically connected to a USB power supplying port through the USB charging port to receive a supply voltage, the power management circuit comprising:

• a USB detection unit, coupled to the USB charging port, determining the type of the USB power supplying port connected to the USB charging port being a Standard Downstream Port (SDP) or a Dedicated Charging Port (DCP);
• a voltage detection unit, coupled to the USB charging port, detecting the supply voltage;
• and
• a control unit, coupled to the USB detection unit and the voltage detection unit, configuring a system power consumption of the portable electronic device based on the type of the USB power supplying port and the supply voltage;
• wherein when the portable electronic device initiates the booting process with the USB power supplying port being the DCP and the supply voltage being lowered than a threshold, the control unit reduces the system power consumption of the portable electronic device maintaining the supply voltage above the threshold for the portable electronic device to initiate the booting process normally.