In early USB chargers, due to the lack of standard specifications. Versatility is the main concern of USB chargers. In view of this, the USB-IF organization has released battery charging specifications. And defines different power supply types, such as SDP, CDP and DCP. However, with the increase in the functions of smartphones, the charging power of 7.5W cannot meet people's needs. In some applications, It is also required that data transmission and power transmission can be carried out at the same time, and USB PD came into being.