- Different "Languages" (Protocols)
QC 2.0: Uses the D+ and D- data lines of a USB cable to negotiate voltage by changing the DC voltage levels on those pins.
USB PD: Uses a dedicated CC (Configuration Channel) line inside the USB-C cable to send high-speed digital data packets for negotiation.
- Physical Interface
QC 2.0 was designed for USB-A to Micro-USB cables.
USB PD requires a USB-C to USB-C (or USB-C to Lightning) connection to utilize the CC pin.
USB Charging Compatibility Matrix
| Power Source (Charger) | Device (Load) | Result | Protocol Negotiation |
|---|---|---|---|
| QC 2.0 / 3.0 | USB PD (e.g., Pixel/iPhone) | Slow (5V) | Fails; defaults to standard USB power |
| USB PD | QC 2.0 / 3.0 | Slow (5V) | Fails; CC pins vs D+/D- mismatch |
| QC 4.0 / 4+ / 5.0 | USB PD | Fast | Compatible (QC 4+ is built on PD) |
| Multi-Protocol | Any | Fast | Charger chip auto-detects protocol |
- Important Exception: QC 4.0 and Newer
Starting with Quick Charge 4.0, Qualcomm made their technology compatible with the USB PD standard.
QC 2.0 / 3.0: Proprietary and Incompatible with PD.
QC 4.0 / 4+ / 5.0: Built on top of USB PD, so they are compatible.