**Charge Technology Should Address the Key Issues First: Battery Acceptance**
When it comes to charging, the main goal is to efficiently transfer energy to the battery. However, before anything else, the battery's ability to accept charge must be considered. Take popular devices like the iPhone X Plus, Huawei P9, Le 2, and Xiaomi Note as examples. These phones typically have batteries with capacities of up to 3000mAh. At a maximum voltage of 4.35V, the theoretical maximum charging power for a 1.5C charge rate would be around 20W. That’s the upper limit.
But this isn’t just about power. It also involves current acceptance. A 1.5C charge on a 3000mAh battery means a current of 4.5A. This requires optimized battery contacts and internal current pathways to handle such high currents without overheating or damaging the battery.
**Second: The Power Supply Capability of the Adapter**
While 20W may seem easy for an adapter, the real challenge lies in the interface’s ability to support that power. Traditional MicroUSB ports are limited to a maximum of 2A at 5.25V, which only gives about 10.5W—far below what 20W requires. To solve this, two options exist: increase current or boost voltage.
Without changing the physical interface, increasing current is not feasible. So, boosting voltage became the standard in the MicroUSB era, leading to Qualcomm’s Quick Charge (QC) technology. The QC standard recommends a current of 1.5A because 2A is the maximum MicroUSB can handle, and most manufacturers avoid pushing devices to their limits to ensure safety and longevity.
However, some companies like OPPO took a different approach by modifying the MicroUSB port with additional pins to allow higher currents (up to 4.5A), keeping the voltage at 5V and achieving over 20W of power. With the introduction of USB-C, these limitations are largely eliminated, as the Type-C port supports up to 5A, making fast charging more efficient and safe.
**Third: Phone Charging Management and Cooling Capacity**
Efficient charging also depends on the phone’s internal management system and its cooling capabilities. The process of voltage conversion and constant current control can lead to efficiency losses and heat generation. Ideally, the charging should be managed externally, reducing the load on the device.
In this context, Qualcomm’s QC protocol has some disadvantages. High voltage and low current input requires internal conversion to lower voltage and higher current, which can cause significant heat buildup. This makes cooling more challenging, especially in smaller devices.
Moreover, the USB-C and USB PD standards have strict rules about adjusting voltage without using USB PD. Qualcomm tried to integrate both QC and PD into USB-C but was unsuccessful. As a result, QC faces potential obsolescence in the future. However, Qualcomm has already started integrating USB PD negotiation into its latest processors to stay competitive.
**USB-PD Fast Charging Communication Principle**
The USB-PD communication protocol uses a 24MHz FSK signal modulated onto the VBUS line to enable communication between the device and the charger. This signal is coupled through a capacitor and filtered out using an inductor to prevent interference with the DC voltage.
The process works as follows:
1. The USB-OTG PHY detects VBUS voltage and checks if the ID pin is pulled down to 1K, indicating support for USB PD.
2. It then performs standard charger detection and initiates the USB PD policy manager.
3. The policy manager decodes the FSK signal to determine the charger’s supported voltages and currents.
4. The device selects a suitable voltage/current pair and sends a request via FSK.
5. The charger responds with an "Accept" message, adjusting its output accordingly.
6. The device dynamically adjusts the charging parameters during the process to optimize speed and safety.
**QC 3.0 Fast Charge Protocol – CX7916**
The CX7916 is a USB charging interface control chip designed for Qualcomm QuickCharge 3.0. It enables adaptive charging of HVDCP, significantly reducing charging time by up to 75%. It automatically identifies the connected device and delivers the optimal current.
It supports various charging standards, including Apple 2.1A/2.4A, Samsung Galaxy Note 2.0A, BC1.2, and YD/T1591. If a device doesn’t support QC 2.0 or 3.0, it defaults to 5V output, ensuring compatibility with older devices.
Key features include support for QC 3.0 Class A/B, intelligent recognition of USB interfaces, wide operating temperature range, low power consumption, and multiple package options.
**Difference Between USB-PD and QC Protocols**
USB-PD is a versatile protocol that supports up to 100W of power and data transmission over a single cable. It works with USB Type-C, which is a reversible connector supporting new standards like USB 3.1, DisplayPort, and USB-PD. While Type-C ports default to 5V/3A, they can support up to 100W when USB-PD is enabled.
However, having a Type-C port does not automatically mean it supports USB-PD. The protocol must be implemented separately. In contrast, QC is a proprietary protocol developed by Qualcomm, mainly used with MicroUSB and later adapted for Type-C, but with less flexibility compared to USB-PD.
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