BC1.2 definition
BC1.2 (Battery Charging v1.2) is a protocol developed by the BC (Battery Charging) group under the USB-IF, which is mainly used to regulate the needs of battery charging. The protocol was first implemented based on the USB2.0 protocol.
BC1.2 charging port
The USB2.0 protocol stipulates that the maximum value of the current drawn by the peripheral device from the USB charger is 500mA, and the current limit of 500mA cannot meet the increasing demand for fast charging. Therefore, BC1.2 introduced the charging port identification mechanism, which mainly includes the following USB port types:
1. Standard downstream port (SDP)
The SDP port supports the USB protocol, the maximum current is 500mA, and it can be considered that the SDP is an ordinary USB interface
2. Dedicated charging port (DCP)
DCP does not support data protocols, supports fast charging, and can provide large currents. DCP is mainly used for special chargers such as wall chargers
3. Charging downstream port (CDP)
CDP supports both data protocols and fast charging
BC1.2 protocol identification process
1. VBUS Detect Vbus detection
There is a circuit in PD (portable device) to detect whether VBUS is valid. The circuit has a reference value. Above this value, it is considered that VBUS is valid. The reference value is not fixed and is generally between 0.8V and 4V
2. Data Contact Detect
This stage is not necessary because the USB port may or may not support the data protocol. If the D + or ID PIN connection has not been detected after a timeout of 900ms at this stage, it is required to start Primary Detection.
3. Primary Detection
The main function of this stage is to determine whether the port is a charging port or a data port:
First pull PD + to 0.6V, then detect the voltage of PD-, if it is less than the specified reference voltage, the port is the data port SDP; if it is greater than the reference voltage, it is the charging port CDP or DCP.
4. Secondary Detection
The role of this stage is to confirm whether the charging port can support the data protocol, that is, to distinguish between CDP and DCP:
First pull PD- to 0.6V, and then detect the voltage of PD +. If it is less than the specified reference voltage, the port is CDP; if it is greater than the specified reference voltage, the port is DCP.
The following figure is the identification process of the CDP port. After the first detection, enter the second detection stage, first pull PD- high, and then judge that the voltage of PD + is less than the reference voltage 0.4V, indicating that the port is a CDP port.
Private fast charge agreement
Since BC1.2 is not a mandatory agreement, many manufacturers have developed their own private fast charging protocols based on BC1.2. For example, Qualcomm's QC2.0 / QC3.0, MediaTek's PE (Pump Express) / PE +. Because the charging power is related to voltage and current P = UI, increasing the voltage or current can increase the charging power. In the case of a certain battery capacity, the larger the power, the faster the charging speed. The technical principles of Qualcomm's QC2.0 / QC3.0 and MediaTek's PE fast charging solution are the same. Both increase the charging power by increasing the charging voltage.
The following figure is the Qualcomm High Voltage DCP protocol identification process. It can be seen that the first test and the second test meet the requirements of BC1.2. The initial VBUS voltage is 5V, and after identifying the DCP port, the VBUS is pulled up to 9V. QC2.0 supports three voltages of 5V, 9V, and 12V. Based on this, QC3.0 subdivides the voltage range to 200mV, and at the same time widens the voltage range to 3.6V ~ 20V.
Line loss compensation
It is known from U = IR that the greater the charging current, the greater the voltage drop on the USB charging line. Especially in in-vehicle devices, with the growth of the USB cable or the increase of the charging current, the voltage reaching the mobile phone terminal may not reach 5V, and such problems can be solved by line loss compensation.
Status and development trend
The current fast charging technology is mainly divided into two camps: low voltage fast charging and high voltage fast charging .
Low-voltage fast charging is represented by OPPO's VOOC flash charging, which increases the charging power by increasing the charging current.
Advantages: low calorific value and high energy conversion efficiency
Disadvantages: hardware needs to be customized, high cost, poor compatibility
High-voltage fast charging is represented by Qualcomm QC2.0. The technical principles of other manufacturers are based on BC1.2 like Qualcomm, and the charging power is increased by increasing the charging voltage.
Advantages: good compatibility, good inheritance, and stability
Disadvantages: high heat generation, low energy conversion efficiency
At present, Qualcomm's fast charging solution occupies most of the market, but with the introduction of the PD protocol (Power Delivery protocol) by the USB-IF organization, it is expected to unify the fast charging market. The maximum power of the PD charging protocol can support 100W, which can meet the charging needs of mobile phones and even notebooks. PD supports two-way power transmission and networking power supply strategies. The latest QC4.0 already supports the PD fast charging protocol.
reference:
https://blog.csdn.net/liglei/article/details/22852755
https://zhuanlan.zhihu.com/p/25588452
https://blog.csdn.net/stoic163/article/details/79291420
BC1.2 definition