Interpretation of usb-if bc1.2 charging protocol

BC1.2 yes USB2.0 The first use Vbus=5V Conduct USB A protocol for docking charging , The agreement was signed by USB-IF The association is in 2010 year 10 Published in , Based on the USB 2.0 Of Vbus Power supply , The maximum supply current is 500mA, Agreement passed USB Of D+/D- Complete and identify support BC1.2 After detection of , from Vbus Supply current for charging . The types of charging ports involved are ：CDP（Charging Downstream Port Charging port , Capable of charging USB Interface ）、DCP（Dedicated Charging Port Dedicated charging port , No, USB Data transmission function CDP Or specially used for charging USB Interface ）、ACA（Accessory Charger Adaptor）、ACA-Dock etc. .

Vbus Detect+Data Contact Detect It's actually testing 4 Line physical contact , You can think of it as one attach event , and primary detection+secondary detection+ACA detection It is to distinguish equipment types , It can be understood as a connect event . The most commonly used logic is voltage comparison , such as Vbus Greater than VOTG_SESS_VLD Internal effective voltage threshold （0.8~4.0V）, The first step is success , The device is connected to an active circuit . When DCP When the interface device is the charger ,PD Port devices such as mobile phones , stay D+ Upper output current （IDP_SRC）, And then detect in D- Upper voltage value , To confirm D+/D- Whether the pins are successfully connected , That is, it is often said to pass D+ and D- A short circuit , come together , The mobile phone sends a signal to identify through communication D+,D- A state of , D+,D- Connected together , Judgment goes into BC1.2 Charge agreement . But this step of the agreement is not mandatory , You can also timeout to enter the next step of detection , Some mobile phone manufacturers' private protocols implement their own protocols by detecting different voltage values , Not through D+/D- The way they are connected , But by testing D+/D- The voltage value of these two lines . The voltage value of each manufacturer is not completely different , Such as D+:2V,D-:2.7V, This is an apple 5W（5V1A）iphone6 The following models of equipment ,D+:2.7V,D-:2V, This is an apple 10W（5V2A）iphone6 Equipment of the above models ,D+:2.7V , D-:2.7V, This is an apple 14W（5V2.4A）IPHONE7 The above models ,D+:1.2V , D-:1.2V, This is samsung 10W（5V2A） Charging mode .

  At present, many products on the market are as follows , With USB-C and PD The rise of the agreement , It will be more and more unified in the future .