Due to the high efficiency and relatively small size of the integrated Class D audio power amplifier, and in most cases, no or only a small area of heat sink is required, greatly reducing the overall size, making it the preferred choice in audio electronics products. However, when using the same layout area in the design of Class D power amplifiers, the on-resistance of pMOS transistors is much greater than that of nMOS transistors. In order to reduce the layout area and the H-bridge on-resistance of the output stage of Class D power amplifiers, nMOS transistors are used for the H-bridge. In order to equalize the overdrive voltage of the LDNMOS transistors at the high and low ends of the H-bridge, it is necessary to add an additional high-level power supply to drive the high end of the H-bridge. Therefore, it is necessary to use a capacitor bootstrap circuit based on a charge pump to generate a high-level. This not only improves the driving efficiency, but also reduces the need for multiple external power supplies, cleverly realizing the driving of the H-bridge of the Class D power amplifier.