Definition and working principle of fast charging QC2.0/3.0 protocol

What is the Quick Charge QC2.0/3.0 protocol?

1. QC2.0 protocol

QC2.0 is the Quick Charge 2.0 technology, which is the 2.0 version of the fast charging technology released by Qualcomm. QC2.0 technology was integrated with the fast charging solution when Qualcomm launched Snapdragon 800 in 2013. There are fast charging chargers that support mobile phones and other mobile devices that support the QC2.0 protocol for fast charging.

Chargers based on the QC2.0 protocol can output four voltage groups: 5V, 9V, 12V, and 20V, and there are two standards: ClassA and ClassB. The ClassA standard QC2.0 protocol supports three voltage groups: 5V, 9V, and 12V, and the ClassB standard QC2.0 protocol supports four voltage output groups: 5V, 9V, 12V, and 20V. Since 20V is not commonly used, the chargers and power banks on the market are mainly based on the ClassA standard.

2. QC3.0 protocol

QC3.0 is an upgraded version of QC2.0. The biggest improvement is that QC3.0 supports output voltage changes of 0.2V per gear. QC2.0 only supports four sets of fixed voltage outputs, while QC3.0 supports output voltages from 3.6V to 20V.

Similarly, the QC3.0 protocol also has ClassA and ClassB. The ClassA standard QC3.0 supports output voltage variations from 3.6V to 12V, and the ClassB standard QC3.0 supports output voltage variations from 3.6V to 20V. Similarly, chargers and power banks on the market are mainly based on the ClassA standard.

Working principle of QC2.0/3.0 protocol

1. Quick Charge QC2.0

The working principle of QC2.0 is that the device (such as a mobile phone that supports fast charging) outputs a voltage signal to the charger through the USB data communication port D+/D-. The charger has a built-in USB input decoding chip, and then the charger will output the target voltage.

Let’s put it this way, QC2.0 increases the output voltage and charging power under the charging current limit to reduce the charging time.

For example, an ordinary mobile phone is charged at 5V1A, but if it supports fast charging, it can be increased to 9V1A or 12V1A, so that the charging power becomes larger and the charging is faster. However, it should be noted that the manufacturer of the charger itself designs the output power to be greater than or equal to 12W, otherwise it is impossible to reach 12V1A.

When a device that supports the fast charging protocol is charged with a fast charging charger, assuming that the charger is at maximum output power, the output may be 5V2.4A, 9V1.33A, or 12V1A.

The above figure is the internal block diagram of the QC2.0 chip CHY100. The D+ and D- signal pins are used for device communication. The voltage on D+ and D- on the device is detected to determine which switch tube of N1/N2/N3 to open.

The charger output voltage = (upper voltage divider resistor/lower voltage divider resistor + 1) x 2.5V, R4 is the upper voltage divider resistor and will not change. If you don't understand the charger voltage regulation and voltage division, you can read the knowledge of switching power supply.

If N1 is turned on, R5 and R6 will be connected in parallel, and the resistance will be smaller than before, that is, the lower voltage divider resistance of the output voltage stabilization circuit will be smaller, and the output voltage will increase to 9V. Similarly, if N1/N2 are all turned on, then R5, R6 and R7 are connected in parallel, the lower voltage divider resistance will be smaller, and the output voltage will increase again to 12V. If N1/N2/N3 are all turned on, then R5, R6, R7, and R8 are connected in parallel, the lower voltage divider resistance will be smaller, and the output voltage will increase again to 20V. See the figure below for details.

2. Quick Charge QC3.0

The principle of QC3.0 is similar to that of QC2.0, except that the voltage output selection of QC3.0 is more flexible.

When using QC3.0, the portable device submits voltage selection requests through the D+ and D- signals of the USB interface, and there may be irregular USB data communications at the same time.

QC3.0 is equivalent to QC2.0 in discrete mode, and selects VBUS through static D+/D- values ​​with three-level logic of 0V, 0.6V, and 3.3V; in continuous mode, the new QC3.0 increases or decreases VBUS in small steps of 200mV, allowing portable devices to choose the most suitable voltage to achieve ideal charging efficiency, which is more flexible. Its maximum load current is limited to 3A and the maximum power can reach 60W.

The above is just a brief introduction to the knowledge of QC2.0 and 3.0. Students who want to learn in depth can search for more information online.