**Charge Technology Should Address Key Issues First: Battery Acceptance**
When it comes to charging, the primary concern is how well the battery can accept power. For example, devices like the iPhone X Plus, Huawei P9, Le 2, and Xiaomi Note have battery capacities of up to 3000mAh. With a maximum voltage of 4.35V, the theoretical peak charging power under 1.5C charging is approximately 20W. However, this is the upper limit. Beyond just power delivery, the battery's current acceptance must also be considered. At 1.5C, a 3000mAh battery would need a charging current of 4.5A, which means the internal battery contacts and current transfer structures must be optimized to handle such high currents.
**Second: Adapter Power Supply Capability**
While 20W may seem manageable for an adapter, the limitations of traditional interfaces come into play. The MicroUSB port, for instance, has a maximum current rating of 2A and a voltage limit of 5.25V, resulting in only 10.5W of power. To meet 20W requirements, either the current or voltage must be increased. Without changing the physical interface, increasing current becomes impractical, so boosting voltage was the solution during the MicroUSB era—leading to Qualcomm’s Quick Charge (QC) technology. The QC standard recommends 1.5A as a safe current, avoiding the 2A limit that could potentially damage the interface. Some manufacturers, like OPPO, took a different approach by modifying the MicroUSB connector with additional pins to allow higher currents while keeping voltage at 5V, achieving over 20W without voltage boosts.
The introduction of the USB-C interface resolved many of these issues, as it supports up to 5A of current, making fast charging more efficient and safer across a wide range of devices.
**Third: Mobile Phone Charging Management and Cooling Capacity**
Charging management involves voltage conversion and constant current control, which can reduce efficiency and generate heat. Ideally, the phone should not handle these processes internally, leaving them to the external charger. However, QC’s high-voltage, low-current approach requires internal conversion, leading to more heat generation. This is a major drawback from a thermal management perspective. Additionally, the USB-C and USB-PD standards strictly prohibit adjusting charging voltages outside of the PD protocol, which has led to conflicts between QC and PD. While Qualcomm tried to integrate both protocols into USB-C, the USB-IF organization rejected the idea, favoring PD exclusively. As a result, QC faces obsolescence, though recent processors now support USB-PD negotiation.
**USB-PD Fast Charging Communication Principle**
USB-PD communication uses a 24MHz FSK signal modulated onto the VBUS line, allowing the device and charger to exchange data. This signal is coupled through a capacitor and filtered out using a low-pass filter to avoid interference with the DC voltage. The process involves several steps:
1. The USB-OTG PHY detects VBUS voltage and checks if the cable supports PD.
2. It then identifies the charger and starts the PD device policy manager.
3. The phone decodes the CapabilitiesSource message to determine available voltages and currents.
4. It selects a suitable voltage/current pair and sends a Request message.
5. The charger responds with an Accept message and adjusts its output.
6. The phone dynamically updates the charging parameters throughout the process.
**QC 3.0 Fast Charge Protocol – CX7916**
The CX7916 is a charging interface control chip designed for USB mobile devices. It supports the Qualcomm QuickCharge 3.0 specification, allowing adaptive charging based on the device’s needs. It can adjust the HVDCP output voltage to significantly reduce charging time—up to 75% faster than conventional methods.
The chip automatically detects the connected device and ensures it receives the optimal current. It is compatible with Apple, Samsung, and other modern devices, and it safely defaults to 5V if the device does not support QC 2.0 or 3.0.
**Key Features:**
- Supports QuickCharge 3.0 Class A and B
- Intelligent USB charging recognition
- Compatible with Apple 2.1A/2.4A, Samsung Galaxy Note 2.0A
- Complies with BC1.2 and YD/T1591 standards
- 4kV ESD protection
- Wide operating temperature (-40°C to 125°C)
- Ultra-low power consumption (1mW at 5V)
- Available in SOP-8 and SOT23-6 packages
**PD vs. QC Protocol: What’s the Difference?**
USB-PD is a versatile protocol that supports up to 100W of power and data transfer over a single cable. It works with the USB-C connector, which supports various standards like USB 3.1, DisplayPort, and PD itself. While USB-C ports can deliver up to 5V/3A by default, they can support up to 100W when PD is enabled. However, having a USB-C port doesn’t automatically mean it supports PD. The protocol is essential for advanced fast charging, especially for high-capacity batteries found in modern smartphones and laptops. In contrast, QC focuses on voltage boosting for faster charging but lacks the flexibility and broader compatibility of PD.
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