The QC (QuickCharge) protocol

You might want to check the two related projects :

• QC Fab : atTiny-412 based, super light, small and efficient
• XIAO QC : based on a XIAO, microPython implementation, with rotary voltage ajustment and screen (to be added) : “almost” replace a lab power supply

QC (Quick Charge) VS USB PD (Power Delivery)

Quick Charge and Power Delivery stand out as two prominent players, each with distinct features and specifications.

Quick Charge is often associated with Qualcomm Snapdragon-powered devices, while Power Delivery is more commonly found in a wide array of devices due to its open standard nature.

While both technologies aim to provide rapid charging, USB Power Delivery offers broader compatibility and versatility, especially with the rise of USB Type-C as a universal standard. However, Quick Charge remains popular for its efficiency and fast-charging capabilities in Qualcomm-powered devices. My choice of investigating QC is essentially linked to the USB connector (see below) and the pretty simple protocol.

Quick Charge

Quick Charge, developed by Qualcomm, utilizes a protocol that typically relies D+ and D- pins of USB Type-A or Type-C connectors. This also means that those communication lines are not available for actual USB communication when Quick Charge is used.

So :

• You’ll only need a simple USB connector with classical GND, D+, D-, VBUS lines. A Type-A connector (or microUSB or miniUSB) will work fine. Which is good.
• You won’t be able to communicate through USB while using this Quick Charge trick. Which is sad.

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(img credit Simon Eugster on wikipedia )

Power Delivery

On the other hand, Power Delivery (PD) is an open standard established by the USB Implementers Forum (USB-IF). It operates using the USB Type-C connector, which supports a versatile array of functions beyond charging, such as data transfer and video output. PD can negotiate power delivery between devices, allowing for a range of voltages and currents, through the additional USB wires/lines (. This flexibility makes it suitable for various devices, from smartphones to laptops and beyond.

So :

• You’ll need a Type-C connector and proper routing of very small line. Good luck with that. (but please let me know if you do)
• You’ll be able to communicate and power your board while using PD. Which would be definitely great.

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(img credit Chindi.ap on wikipedia )

The Quick Charge protocol

The CHY103 datasheet provide a good overview about the QC3 protocol : handshake and voltage selection. Voltages are selected based on three voltage levels applied to D+/D- pins :

• 0V
• 0.6V
• 3.3V

CHY100 datasheet specifies voltage thresholds of 0.325V and 2V, so 0.6V is a safe (and generally documented) value for the “intermediary” voltage.

• There are two “classes” for QC power :
  • Class A max voltage is 12V
  • Class B max voltage is 20V
• Minimum voltage is supposed to be 3.6V or 3.2V but I actually measured the lowest voltage to be ~4V on most power supply.

The QC protocol in brief :

• Starts with ~2sec handshake : D+ is set to 0.6V and D- is left floating. The charge will try to pull D- at the D+ and if D- remains floating for about 2sec, the charger will enter QC mode.
• Voltage is then set by changing D+ and D- voltages values.

QC2.0 voltages (fixed “standard” voltages) :

NB : this table and QC protocol makes me think it would be feasible to “negociate” a fixed 12V voltage and seeing it using just 1 LED + 5 resistors (and no microcontroller at all…)! Will test is “soon”.

• RED LED (~2V)
• 2.2k resistor to limit led current
• Resistor bridge devider in parallel of the led : GND-470ohm-1kohms (to get ~0.6V
• Two 1k resistors (or 2.2k?) to D+ and D- to “protect” lines

This should provide a near zero current through led when line = 5V, then set line to 12V and make the led get a 3.19mA when line is set (making it visible). Can’t wait to test that!

QC3.0 addition (0.2V steps) :

After each glitch, the signals must return to “coutinous mode” (D+ = 0.6V, D-=3.3V). Glitches are 5ms in this code.

A more detailed explaination about the protocol and the code is documented in the arduino code commented head section.