USB_PD protocol fast charge mobile power design
In order to realize the high-power power transmission of mobile power and save the charging time, a fast-charging mobile power was designed in combination with the USB P D fast charging protocol. This design uses the EDP3010 reconfigurable digital power chip of Eneng Microelectronics Technology Co., Ltd. as the controller. By constructing related hardware circuits and writing the corresponding software, fast charging based on the USB P D protocol is realized. Function, the maximum power for charging four strings of lithium battery packs can reach 90 W, fast charging for electronic devices supporting USB P D protocol, the maximum output power can reach 65 W, and it has multiple protection functions It can ensure the safe progress of the charging and discharging process.
With the advent of the smart era, electronic devices such as mobile phones, tablets, and laptop computers have also become more intelligent and large-screen. In the course of sexual progress, research can only be conducted by increasing the battery capacity or increasing the charging speed. Increasing the capacity will lead to a substantial increase in the volume and quality of the device. Therefore, under the appropriate capacity, increasing the charging rate is a more reasonable and effective way, and fast charging technology came into being under this background.
In the current market, mobile power is gradually shifting from low power to high power power transmission.The fast charging protocol is the key technology to achieve high power transmission, especially the development of smart phone related fast charging technology.Each major manufacturer has launched its own fast charging. Protocols, such as the QC protocol launched by Qualcomm platform, the FCP and SCP protocols launched by Huawei, the PE protocol launched by MediaTek, the VOOC flash charging technology launched by OPPO, and the USB_PD protocol launched by USB_IF. Among them, the USB_PD protocol is a fast charging protocol based on the Type_C interface. Today, the USB_PD protocol occupies a natural advantage with the increasing popularity of the Type_C interface, and it will be the mainstream fast charging protocol in the future.
The mobile power supply designed in this article supports the USB_PD fast charge protocol, and the maximum power transmission can reach 100 W, which just reaches the maximum power transmission limit value of the Type_C interface, which greatly shortens the charging time and provides users with travel It's convenient. After experimental tests, the USB_PD fast charge protocol has good compatibility.It can charge a variety of electronic devices that support the USB_PD fast charge protocol, and also supports other adapters with the USB_PD fast charge protocol to quickly charge the mobile power in this design On the other hand, the system has various protection functions to ensure the safe use of mobile power.
The USB_PD protocol is a power transmission protocol based on the Type_C interface. First, the pins of the Type_C interface are introduced. A total of 24 pins are divided into two rows in a symmetrical form. b> 12 pins, including 4 GND and 4 V + can be used for power transmission, which can also support 100 The basis of W fast charging, there are 1 CC pins on the top and bottom of the interface connected to the CC line. The CC line is the channel for USB_PD protocol data transmission, and the communication between the devices is performed through the CC line single line. It belongs to half-duplex. The other pins of the interface can be used for data or audio signal transmission. It is not covered in the USB_PD protocol, and will not be described too much. The Type_C interface pins are symmetrically distributed, so it also has the advantage of supporting blind insertion. It is not necessary to distinguish the front and back sides, which provides convenience for use.
The party that supplies power in the protocol is called the Source side, and the receiver is called the Sink side. During the USB_PD protocol power negotiation process, the two parties need to communicate through the CC line and complete the energy supply negotiation to select the appropriate gear; this design is used as an example to introduce the negotiation In the process, when the mobile power source is used as the source, once it is detected that the CC line is pulled down, that is, a device is inserted in the Type_C interface, it will broadcast periodically through the CC line. The broadcast content is the power supply capacity of the mobile power source. V / 3 A, 9 V / 3 A, 12 V / 3 A, 15 V / 3 A, 20 V / 3.25 A five gears; The Sink terminal selects a gear after receiving the energy supply information sent by the Source, and then sends a request for the gear to the Source; after the Source receives the request information and confirms that it meets the energy supply range, it sends a consent to the Sink. The information is applied, and it is ready to be adjusted to the power level required by the Sink; there is a CRC check in the entire data communication process to ensure the accuracy of data transmission.
In this article, a EDP3010 programmable power management chip is used as the control core, and the topology of the buck-boost circuit is the main circuit, combined with the insertion detection module, lithium battery protection module, over-temperature protection module, and four lithium battery packs The peripheral circuits constitute the entire system.
When the charger is connected to the USB Type_C interface of the plug-in detection module, after the plug-in test is performed, the control core confirms that it is a charger, then turns on the switch to flow through the DC converter, and drives the main circuit according to the input voltage The switch tube on the upper side makes it work in a step-down or boost state, and then connects to the positive electrode of the lithium battery, and finally forms a complete loop through the switch tube controlled by the lithium protection chip; the switch tube controlled by the lithium protection chip is connected in series with the battery Between the negative electrode and the ground electrode, this switch can control the on and off of the entire system circuit, so that timely protection can be achieved when the lithium battery is in abnormal working conditions. In the entire working process, in addition to the lithium battery protection chip to protect the system, there are functions such as over-temperature protection module, over-current protection, under-voltage protection and over-voltage protection, all of which are controlled by the controller through AD Collect voltage and current data for protection. When the system works in discharge mode, the basic working process is the same, but the current and voltage flow are different.
EDP3010It is a programmable digital power management chip. It is the control core of the entire system. It has powerful functions and strong driving capabilities. It has multiple ADC channels and the maximum number of sampling bits can reach 16 bit, which integrates the hardware platform required to implement fast charging technologies such as the PD protocol and the QC protocol, with a comprehensive system management module that can support a variety of Topology structure, can quickly complete the required power system management according to demand.
Circuit structure of the main circuit module. The BAT terminal is a battery pack consisting of four nominal 3.7 V lithium batteries connected in series. The voltage range is 12 V ～ 16.8 V , when When using a power supply device such as a 5 V adapter to charge the system from the V + input, you need to boost the voltage through the main circuit to charge the lithium battery pack. b> USB_PD protocol adapter, the input voltage can reach 20 V through power negotiation. At this time, the main circuit needs to be stepped down to charge the lithium battery pack, so from The V + input requires the system to determine whether to make the main circuit work in Boost mode or Buck mode according to the input voltage; when V When the + terminal is a powered device, the voltage range of the BAT terminal is 12 V to 16.8 V , and the V after the USB_PD protocol negotiation The output voltage of the + terminal may be 5 V, 9 V, 12 V, 15 V, 20 V. It also needs buck-boost conversion. The four-tube buck-boost circuit shown in Figure 3 can meet the system requirements and achieve two-way buck-boost conversion.The direction of charging the lithium battery with the V + input is For example, when the input voltage is lower than the lithium battery voltage, Q 4 constant off, Q 3 Continuous conduction, using two complementary PWM waves to drive Q 1 , Q 2 to make the converter work in Boost mode; when the input voltage is higher than the lithium battery voltage, Q 1 Constant on, Q 2 Constant off, Drive Q 3 ,
The plug-in detection module has two interfaces, a USB Type_ A interface and a USB Tpye_C interface. Among them, the USB Type_A interface is the OUT fast release port in 4 , D +, D -for data Communication, this interface is only used for system output discharge; when the system is in standby state, the LDO of 3.6 V will be OUT2 The potential of the network is raised, and the control core judges by the potential of OUT2 . Once the potential is pulled low, the control core detects a low level to determine that a load is inserted, and then starts System and turn on the switch Q 2 , and start to output power to the load; USB Tpye_C The interface is a two-way interface, which can be used as both an output interface and an input interface.The judgment logic of this interface is as follows: When the system is in standby, the CC line on the interface is continuously pulled up and down. When the load is connected in the CC pull-up state, it can be detected that the load pulls down the CC line voltage. At this time, it is determined that the load is connected and the system starts to supply power to it; When a charger is inserted into the C port, the voltage of the charger will be detected when the CC line is in the pull-down state, and the C port is detected in the pull-down state. Voltage access After some time, the charger determines access.
The design of the lithium battery protection circuit is to prevent the lithium battery from overcharging and overdischarging during the charging and discharging process; this circuit module uses the HLT6034A lithium battery protection chip, which can monitor a single battery, and it is normal. Under working conditions, the MOSFET external to the lithium battery protection circuit is in a conducting state. Once the lithium battery protection chip detects an abnormal situation, it will immediately turn off the switch tube to power off, thereby achieving the lithium battery protection function. The main control chip is also monitoring whether an abnormal situation occurs.Since the lithium battery has a problem, it will cause serious consequences.When it is protected by software, it is also protected by hardware, which can effectively improve the overall system during charging and discharging. safety.
Auxiliary power is mainly used to power the power management chip. Using 3.6 V low-dropout linear regulated power chip ME6203 , this chip has the advantages of simple peripheral circuits, high withstand voltage, high output voltage accuracy, and low temperature drift, and the cost Lower.
During the charging and discharging process of the lithium battery, its temperature changes greatly, especially in the case of high power. It is necessary to monitor the temperature of the lithium battery in real time to ensure the safe charging and discharging. Power management chip TH The constant current source and AD sampling interface are integrated inside the pin.The thermistor is configured outside the TH pin and placed at the lithium battery. When the temperature changes, the resistance of the thermistor also changes, so the voltage on the TH pin will also change accordingly. The system can collect TH TH pin voltage to obtain the temperature information of the lithium battery; the lithium battery will cause damage to the lithium battery when charging or discharging under low or high temperature conditions, so the safe operating temperature range is set in the system software, exceeding the temperature range Will stop working immediately to ensure the safe operation of the lithium battery;
The system basic charging process and discharge process software design flow. Began after an insert initialized in system testing function, the function of inspection passed from external interface signals, distinguish the is power supply equipment and electric equipment, and chose to enter the quick charge agreement charging or discharging quick charge agreement in the judgment of the function, if detection function is detected by electrical equipment is to jump to discharge handshake protocol, communicate with the electric equipment, if the electric equipment support USB_PD agreement to shake hands is successful negotiation of function, and then enter the power after negotiation started quick charge for the electric equipment, if the electric device does not support into the ordinary 5 V to recharge. The software logic of external power supply equipment is basically the same as above.
The basic function test is carried out by using electronic load meter and simulated battery. The test result is basically the same as that of actual lithium battery, but it is more convenient to obtain voltage, current and other data than lithium battery. The standby current of the system was only 240 uA, and reached 14 mA after awakening the system. Charging efficiency in 5 V and 12 V and 15 V file and 20 V file in 85 % above, and the discharge efficiency in 5 V, 9 V, 12 V, 15 V, 20 V gear are in more than 87 %. The actual test shows that overcurrent protection, overcharge protection, undervoltage protection, overtemperature protection and lithium battery protection are all effective, and the ripple voltage is less than 100 mV.
The charge-discharge cycle test is to perform a complete charge and discharge cycle on the system lithium battery, and record the battery voltage, current and temperature during the entire process. Lithium batteries have a certain internal resistance. The voltage measured at the lithium battery terminal is high when charging at high power, so that the battery cannot be fully charged with a constant current during the charging process. On the other hand, according to the characteristics of the lithium battery during the charging process, The battery cannot be charged with high current when the battery is under voltage, nor can the battery be oversaturated.The system software and lithium battery protection circuit prevent these situations from occurring; the system software uses a constant current first and then constant voltage charging algorithm to charge The previous system first detected the battery status. When the voltage of the four-string lithium battery pack was lower than the safe voltage 12 V , the system first pre-charged with a small current. When the battery pack voltage was greater than 12 V After that, large-current constant-current charging is started.When the battery pack voltage is charged near 16.8 V , it enters the constant-voltage charging mode until the battery pack is fully charged. Charge the lithium battery pack to saturation. The charging test used a 90 W adapter, and the lithium battery pack used four 2 500 mAh lithium batteries in series. The charge and discharge rate of a single lithium battery was 3C. , that is, the battery terminal current can support a maximum of 7.5 A , assuming that the loss is ignored and the power reaching the battery pack is 90 W , even when the battery pack has low power < The current input to the lithium battery reaches 7.5 A at the state of b> 12 V , so it can be guaranteed that the battery pack will not be damaged due to the excessive charging current during fast charging. In actual tests, the pre-charge current is 0.2 A , but the maintenance time is short, and it quickly switches to the constant-current charging stage. The current is 4.6 A; 28 min The battery voltage is close to the saturation voltage 16.8 V . At this time, the battery is switched to the constant voltage charging mode, and the battery is basically saturated after maintaining 10 min . The discharge cycle test is relatively simple. Set the electronic load to the constant current mode and the current level is 3.5 A , and then use a deceiver to increase the system output voltage to 20 V, 50 min The lithium battery is discharged, and the cut-off voltage is 11.88 V . After several tests, the data in the charge cycle and discharge cycle remained basically normal, and the system was stable.
The charging test mainly uses a PD fast charge adapter to charge the system and check whether the charging power reaches the power negotiated in the USB_PD protocol. The adapters used are Kunyang's 18 W PD adapter, Apple's 28 W, 87 W adapter, and a 90 W adapter. PD adapter, of which the Apple 87 W adapter can charge non-Apple devices with a maximum power of 60 W. The maximum power is 90 W.
This design uses the EDP3010 power management chip as the control core, and has completed a maximum charging power of 90 W and a maximum discharging power of 65 W USB_PD protocol mobile power supply, and has corresponding protection functions to ensure the safe charging and discharging of lithium batteries, which can charge electronic devices with different power requirements and support the PD protocol. High-power charging can shorten the charging time and provide convenience for users in daily life. The USB_PD protocol is a fast charge protocol based on the Type_C interface. I believe that under the general trend of the future interface, the use of the USB_PD protocol will be more and more The wider. This design can provide reference and reference for the subsequent research on high-power mobile power based on fast charging technology.
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