Speaking of the USB-PD protocol, the full name of USB Power Delivery may be unfamiliar to many people, but more and more mobile phones have begun to support this protocol and used it as a fast charging function for devices.
Someone with a little understanding may think that the charger output of the USB-PD protocol is output in Type-C, which is different from our common USB-A interface output, but this cannot be simply used to judge whether the USB-PD protocol is supported. The charger that has Type-C output is not necessarily the charger that supports USB-PD protocol; the charger that supports USB-PD protocol must have Type-C output.
PD charger hardware structure
The hardware structure of a typical mobile phone charger (take the Qualcomm QC2.0 fast charge protocol based on the Dialog solution as an example) is shown in Figure 1. As a QC2.0 protocol controller, iW626 negotiates power supply with the mobile phone AP via the D+/D- signal of the USB port, and then controls the primary AC/DC controller iW1780 to adjust the output voltage through the optocoupler.
The charger circuit based on the PD protocol can maintain the AC/DC part unchanged, but the QC protocol controller is replaced with a PD controller, such as the CCG2 (type-cControllerGeneraTIon2) of Cypress Semiconductor. CCG2 is one of the earliest PD controllers certified by USB-IF. It contains ARM®Cortex®-M0 processor and a complete PD protocol transceiver, which can meet various support types such as chargers, hosts, accessories, EMAC cables, etc. The application of -c port has many mass production cases in Apple, Lenovo, HP, Dell, Xiaomi, LeTV and other first-line brand customers.
The schematic diagram of the charger circuit using CCG2PD controller and DialogAC/DC controller is shown in Figure 2. CCG2 communicates with the mobile phone AP through the CC signal of the Type-C port for PD protocol communication, and then controls the voltage and current requirements of the optocoupler through PWM Feedback to AC/DC for output adjustment. CCG2 will sample the VBUS to ensure the reliable operation of the PD protocol state machine, and control the on-off of the VBUS through the MOSFET according to the PD state. In addition, CCG2 can also support the QC3.0 protocol through D+/D-, and realize the coexistence of PD and QC on the same Type-C port (the two cannot be activated at the same time in actual work, and the user can define the priority and enable strategy). In addition to voltage regulation charging, PD fast charging can also perform current adjustment to achieve fine current adjustment or high current charging or even direct charging. CCG2 can use internal ADC for voltage and current sampling, closed-loop control and OVP/OCP/UVP protection. The protection mechanism of CCG2 is software controlled, so the real-time performance is not enough, and it can act as an auxiliary or redundant AC/DC controller protection. Cypress's third-generation PD controller CCG3 streamlines the BOM and integrates protection mechanisms such as internal hardware OCP/OVP, which improves ADC accuracy and provides the best high-current direct charging solution. It has been used by many mobile phone customers. Evaluation design.
What is the PD charging protocol
The PD charging protocol is a power transmission protocol announced by the USB-IF organization. It can increase the current default maximum power of 5V/2A type-c interface to 100W. At the same time, Google announced that the fast charging protocol carried by mobile phones above Android 7.0 must support PD The agreement is intended to unify the fast charging market.
What does PD protocol fast charge mean?
USB-PowerDelivery (USBPD) is one of the current mainstream fast charging protocols. It is a fast charging specification formulated by the USB-IF organization. . USBPD increases power transmission through USB cables and connectors, expanding the power supply capability of the cable bus in USB applications. This specification can achieve higher voltage and current, and can deliver up to 100 watts of power, and can freely change the direction of power delivery.
The relationship between USBPD and Type-C. People often talk about USBPD and Type-C together, and even call Type-C chargers as PD chargers. USBPD and Type-C are actually two different things, USBPD is a fast charging protocol, and Type-C is a new interface specification. The Type-C interface supports up to 5V/3A by default, but after the USBPD protocol is implemented, the output power can be up to 100W as mentioned above. Therefore, many practical Type-C interface devices will support the USBPD protocol.
The development prospects of USBPD. USBPD has now developed to the USBPD3.0 version. Driven by Google, USBPD has incorporated Qualcomm’s QC fast charge agreement and has received support from the Ministry of Industry and Information Technology of China. It is expected to unify the current chaotic fast charging market soon.
Advantages of PD fast charge protocol
PD is PowerDelivery, which focuses on the power transmission process of two or more devices, even a smart grid based on the USB interface. The power transmission can be bidirectional or even networked, and can have a system-level power supply strategy. And QC is that QuickCharge only pays attention to the problem of fast charging, the power transmission is unidirectional, it does not have the ability to network, and does not support other functions except power supply.
USBPD communication is the process of modulating the message of the protocol layer into a 24MHZ FSK signal and coupling it to VBUS or obtaining the FSK signal from VBUS to realize the communication between the mobile phone and the charger.
As shown in the figure, in the USB PD communication, the 24MHz FSK is coupled to the DC level on the VBUS through the cAC-Coupling coupling capacitor. In order to prevent the 24MHz FSK from affecting the PowerSupply or USBHost’s VBUS DC voltage, A low-pass filter composed of zIsolation inductors is added to the loop to filter out the FSK signal.
The principle of US BPD, taking the mobile phone and charger support USBPD as an example, is explained as follows:
1) The USBOTG PHY monitors the VBUS voltage. If there is a 5V voltage of VBUS and the OTGID pin is detected as a 1K pull-down resistor (not OTGHost mode, the ID resistance of OTGHost mode is less than 1K), it means that the cable supports USBPD;
2) USBOTG does the normal charger detection of BCSV1.2 specification and starts the USBPD device policy manager. The policy manager monitors whether the FSK signal is coupled to the DC level of the VBUS, and decodes the message to determine that it is a CapabilitiesSource message, which is parsed according to the USBPD specification This message derives all the voltage and current list pairs supported by the USBPD charger;
3) The mobile phone selects a voltage and current pair from the CapabilitiesSource message according to the user's configuration, and adds the voltage and current pair to the payload of the Request message, and then the policy manager couples the FSK signal to the VBUS DC level;
4) The charger decodes the FSK signal and sends an Accept message to the mobile phone, while adjusting the DC voltage and current output of PowerSupply;
5) When the mobile phone receives the Accept message, adjust the charging voltage and current of the ChargerIC;
6) During the charging process, the mobile phone can dynamically send a Request message to request the charger to change the output voltage and current, so as to realize the fast charging process.