Briefly talk about the identification protocol of mobile port -bc1.2

About BC1.2 agreement Every engineer engaged in mobile phone hardware design should be very familiar with , It is mainly for the identification of charging port . However, about this part of the agreement , There are many explanations on the Internet , Someone said it very carefully , There are also very rough , Xiaobian is also to learn this part of the agreement , Read a lot of information , Finally, I decided to combine what I learned with what I really encountered at work to make some simple descriptions and explanations .

First of all, we need to know a few nouns
SDP：Standard Downstream Port Standard downlink port , For example, the computer USB mouth . The charging capacity of this port is 0.5A
CDP：Charging Downstream Port With strong charging capacity USB mouth , For example, the computer USB mouth . The charging capacity of this port is average 1.5A.
DCP: Dedicate Charging Port Special charging port , Like mobile phone chargers
PD：portable Device Portable devices , Such as mobile phone .
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The figure shows the framework of charging port detection

The identification of charging port is mainly divided into the following five steps ：
(1)VBUS Detect
(2)Data Contact Detect
(3)Primary Detection
(4)Secondary Detection
(5)ACA Detection

This article mainly talks about the first four common stages

1. VBUS testing
   stay BC1.2 Before the start , First of all, it will be done VBUS Detection of . every last PD There is an in-phase comparator inside , Used to detect VBUS. When the adapter is connected PD when , Only the comparator VBUS Greater than the reference voltage VOTG_SESS_VLD when ,VBUS It will work , The following operations will be carried out .
   Additional explanation ： Because the mobile port USB The design of the seat ( The arrow points to VBUS Pin ),TYPE C Terminal VBUS The pin first touches the mobile phone ( remove GND End ), Next is the data pin contact . This is why the charging identification process , The first thing to do is VBUS detect 了 .
   

2. DCD testing
   Data Contact Detect, Data connection line detection , That is, judge whether the adapter is fully connected to the mobile phone USB Transposon .
   End of judgment VBUS After access , Then it is to judge whether the connection of data signals is in place .
   When Attached when
   Mobile phone terminal D+ Of IDP_SRC open , because D+ A resistor is terminated RDP_DWN Go down to the ground , therefore D+ There will be a certain small voltage , When the voltage is less than the reference value , explain USB Good access . So look at the waveform D+ There is a very small voltage fluctuation at the front end .
   
   However DCD The detection of is not necessary , If not implemented DCD Detection of , The agreement will be in VBUS Effective T DCD_TIMEOUT Start the next steps ( The following waveform is not executed DCD Detection ).

3. Charging port detection
   (1) Primary Detection ： distinguish SDP And DCP CDP
   
   When PD Connect to SDP when ,PD The device will open the upper VDP_SRC With the middle IDM_SINK, the D+ There is a certain voltage ( Probably 0.6V), That is, the graphic waveform D+ stay “Primary detection” The higher part in . Then the mobile phone starts to detect D- The voltage of , When D- The voltage is less than VDAT_REF It is thought that what is recognized is SDP. When D- The voltage is greater than VDAT_REF, It is thought that what is recognized is DCP perhaps CDP, Then start the secondary detection .
   SDP

(2)Secondary Detection: distinguish DCP And CDP
CDP

After the first test ,PD Will be in D- End open VDM_SRC, stay D+ End open IDP_SINK, At the same time, compare D+ The voltage at the terminal is the same as VDAT_REF, If it is less than VDAT_REF. It indicates that the connected device belongs to CDP.

DCP

if D+ The voltage at the terminal is greater than VDAT_REF, It shows that the access is DCP, because D+ And D- Through between RDCP_DAT Short circuited together . therefore D+ And D- The voltage is almost similar .

stay DCP After the test , We also need to check whether the protocol supports QC2.0. It will be in D+ End application 0.6V voltage , because DCP Stage ,D+ And D- Short circuited together , therefore D+ And D- The voltage is always the same . Is maintaining 1.25s after D+ And D- Will disconnect the short circuit , if D- The voltage drops to 0V And for a while , Description this adapter supports QC2.0.

stay D- Fall to 0V And maintain it for a period of time ,D+ And D- The voltage continues to change , This is the picture D+ D- The last stage , It follows the following principles , Inform the charger , Output the corresponding voltage .

The waveform in the above figure ：D+ Final 3.3V,D- Final 0.6V therefore VBUS Be raised to 9V.

All in all , Summarize according to the waveform , In the identification phase ,Primary Detect from D+ launch ,Secondary Detect from D- launch .SDP DCP CDP The difference between the three in waveform ,SDP stay Primary Detect Is recognized , All are located only once D+ High level of .DCP because D+ D- Short circuited by resistance , therefore D+ And D- Always maintain the same level , Both are in the high-level state .CDP It is seen as the waveform neutralization of the two ,D+ There is only one high level ,D- There are two high levels .