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All colleagues unite and focus their efforts to write a new chapter of developmentWhat is the PD fast-charging protocol, and what is the communication principle of USB PD fast charging?
所属分类： Industry News
发布时间：2020-05-13
What is the PD charging protocol? The PD charging protocol is a power delivery standard published by the USB‑IF. It enables the Type‑C connector, which currently defaults to a maximum power of 5 V/2 A, to support up to 100 W. Meanwhile, Google has announced that smartphones running Android 7.0 or later must adopt fast‑charging protocols that comply with the PD standard, aiming to standardize the fast‑charging market.
Principles of USB PD Fast-Charging Communication
USB-PD communication involves modulating protocol-layer messages into a 24 MHz FSK signal and coupling it onto the VBUS, or demodulating an FSK signal from the VBUS, to enable communication between the device and the charger.
As shown in the figure, in USB‑PD communication, a 24 MHz FSK signal is coupled onto the VBUS DC level via a cAC‑coupling capacitor. To prevent this 24 MHz FSK signal from affecting the Power Supply or the USB Host’s VBUS DC voltage, a low‑pass filter consisting of an isolation inductor is also included in the loop to attenuate the FSK signal.
The principle of USB PD, illustrated using a smartphone and a charger both supporting USB PD as an example, is explained as follows:
1) The USB OTG PHY monitors the VBUS voltage; if a 5V VBUS is present and the OTG ID pin is detected to be pulled down with a 1 kΩ resistor (indicating that it is not in OTG Host mode—where the ID resistor is less than 1 kΩ), then the cable supports USB PD.
2) The USB OTG performs standard BCSV 1.2‑compliant charger detection and activates the USB‑PD device policy manager. The policy manager monitors whether an FSK signal is coupled to the VBUS DC level; upon decoding the message and identifying it as a CapabilitiesSource message, it parses the message according to the USB‑PD specification to extract the list of voltage and current pairs supported by the USB‑PD charger.
3) The mobile device selects a voltage–current pair from the CapabilitiesSource message based on the user’s configuration, appends this 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 simultaneously adjusting the DC voltage and current output of the power supply.
5) Upon receiving the Accept message, the mobile phone adjusts the charging voltage and current of the Charger IC.
6) During charging, the mobile phone can dynamically send Request messages to prompt the charger to adjust its output voltage and current, thereby enabling fast charging.