The hardware structure of a typical mobile phone charger, based on the Qualcomm Quick Charge 2.0 protocol using the Dialog solution, is illustrated in Figure 1. The iW626 acts as the QC2.0 protocol controller, negotiating power supply through the D+/D- signals of the USB port and the device’s application processor (AP). It then adjusts the output voltage by controlling the primary AC/DC controller, iW1780, via an optocoupler.
When using the PD protocol, the AC/DC circuit remains unchanged, but the QC protocol controller is replaced with a PD controller, such as Cypress Semiconductor’s CCG2. As one of the earliest USB-IF-certified PD controllers, CCG2 includes an ARM® Cortex®-M0 processor and a full PD protocol transceiver, supporting various devices like chargers, mainframes, accessories, and EMAC cables. This technology has been widely adopted by leading brands such as Apple, Lenovo, HP, Dell, Xiaomi, and LeTV.
Figure 2 shows the schematic of a charger circuit using the CCG2 PD controller and the Dialog AC/DC controller. CCG2 communicates with the PD protocol via the CC signal of the Type-C port and the mobile phone's AP. It controls the voltage and current through PWM control and optocoupler feedback to adjust the AC/DC output. By sampling VBUS, CCG2 ensures the reliable operation of the PD protocol state machine and manages VBUS switching via a MOSFET. Additionally, it supports QC3.0 via D+/D-, allowing PD and QC to coexist on the same Type-C port, though they cannot be used simultaneously. CCG2 also enables current regulation for fine-tuning or high-current charging, with internal ADC for voltage and current sampling, closed-loop control, and protection features like OVP, OCP, and UVP. However, its protection mechanism is software-based, making it less real-time than the AC/DC controller.
Cypress’s third-generation PD controller, CCG3, integrates hardware-based OCP and OVP protections, improves ADC accuracy, and provides an optimal high-current direct charge solution. It is being evaluated by multiple mobile phone manufacturers.
What is the PD charging protocol?
The Power Delivery (PD) protocol is a power transmission standard developed by the USB Implementers Forum (USB-IF). It allows the maximum power delivery from a 5V/2A Type-C interface to reach up to 100W. Google requires Android 7.0 and above devices to support PD, aiming to unify the fast charging market.
What does the PD protocol fast charge mean?
USB-Power Delivery (USB PD) is a mainstream fast charging protocol developed by the USB-IF. It increases power delivery through USB cables and connectors, enabling higher voltages and currents—up to 100W—and even bidirectional power transfer. While Type-C is a physical interface specification, PD is a protocol that enhances the capabilities of Type-C ports. Many devices now support both Type-C and PD, allowing for higher power outputs.
The development prospects of USB PD are promising. With the release of USB PD 3.0 and growing industry support, including from Qualcomm and the Chinese Ministry of Industry and Information Technology, it is expected to bring order to the fast charging market.
Advantages of the PD fast charge protocol include bidirectional power transfer, networked power management, and system-level power strategies. In contrast, QuickCharge (QC) focuses only on fast charging, with unidirectional power transfer and no networking capabilities.
Currently, few devices support PD, mainly high-end models like the MacBook, some Meizu and HTC phones, and certain Google notebooks. However, domestic manufacturers are gradually adopting PD chargers, such as the Oerico PD charger TSM-1U, which features a durable design and user-friendly interface.
How does USB PD fast charging work?
USB PD communication involves modulating protocol messages into a 24 MHz FSK signal, which is coupled to the VBUS. A low-pass filter, consisting of an isolation inductor, is added to prevent interference with the DC voltage. The communication process involves the following steps:
1. The USB OTG PHY detects VBUS voltage and identifies if the cable supports PD.
2. The USB OTG performs standard charger detection and initiates the PD device policy manager.
3. The policy manager decodes the FSK signal to obtain the CapabilitiesSource message, listing all supported voltages and currents.
4. The device selects a voltage and current pair, sends a Request message, and couples the FSK signal to VBUS.
5. The charger decodes the FSK signal, sends an Accept message, and adjusts its output.
6. The device receives the Accept message and adjusts its charging parameters.
7. During charging, the device can dynamically send new requests to change the output voltage and current, enabling efficient fast charging.
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