Qualcomm Quick Charge is compatible with USB Type-C where it matters

Quick Charge users don’t have to worry about USB compatibility.

Benson Leung, a Google engineer, has been testing USB Type-C cables across the market to verify they meet the USB Type-C spec. He’s succeeded in getting some poor quality items off Amazon, which is very helpful to consumers.

In November he said Qualcomm’s Quick Charge (QC) technology couldn’t coexist with USB Type-C on the same connector because the latter violates the former’s spec:

While he’s certainly correct that QC violates the USB spec, the situation is lot more nuanced than that, and some of what he said is unfortunately incorrect.

I replied directly to that post, and some of the content of those replies follows.

Let’s get a few things straight about QC first, and then review Benson’s assertions using them:

  1. Unlike the status quo for USB†, OEMs actually have to go through a UL (a worldwide saftey certification organization) certification process for QC, detailed in this Test & Certification Application (PDF). Per page 3 shown below, devices must maintain “the plug-and-play ease of use of USB connectors” to pass certification. This implies that there is no data transfer use case in which a QC device would behave any differently from a non-QC one and certainly none in which the QC device’s behavior would be unpredictable.

    Qualcomm’s description of QC’s USB behavior is buried in a UL certification document.
  2. For all non-QC use cases, QC devices behave like any other normal USB device. Per page 3 above, QC certified devices must support “Conventional USB charging,” defined as “1A at 5V” (though I’m not sure how they get 15W from that. PIV, so power should be 1A * 5V = 5W).

    UPDATE: I contacted Qualcomm about this and got this useless reply:

    Any information other than what is listed on our website (URL listed below for your reference) is Proprietary to Licensees.

    Unfortunately we are unable to assist with your inquiry.  However, we keep a list of compatible devices at Qualcomm.com/quickcharge.  Hopefully this has the answer to your question.

    Otherwise, we recommend you follow-up with a vendor that carries this product and seek their feedback on your technical questions.

    Please note, Qualcomm is the technology provider, not a manufacturer of consumer products and therefore we are unable to answer your product specific question. We hope this direction helps.

    Thank you for your inquiry,
    Qualcomm Technologies Inc.


    FWIW, in my experience QC (2.0) chargers slow charge non-QC devices and don’t (can’t?) fast charge them.

  3. It follows from points 1 and 2 above that QC uses USB data lines for power only when connected directly to an A/C adapter, which has no use for a data line anyway.
  4. While I can’t find any publicly available definition of the QC spec, it’s based on a patented technology called HVDCP (High Voltage Dedicated Charging Port). The “Dedicated Charging Port” detail name implies the tech works for ports that do nothing else but provide power and doesn’t work for data ports. Here’s the patent (which I haven’t read).
  5. Fairly detailed implementation info can be found by searching “HVDCP” on Google. Here’s a very detailed product preview (PDF) by ON Semiconductor for their NCP4371 HVDCP controller.

Points 1 to 3 disprove Benson’s claim that the “Type-A port can’t be used to communicate to your PC at the same time you fast charge” via QC, as QC devices would fail the certification requirements if that were the case. In addition, implementing QC on a PC Type-A port would be disingenuous as it would disable data transfer for QC devices, thus killing most of the Type-A port’s functionality. No PC OEM in their right mind would do that.

The HTC 10LG G5, and all other Quick Charge 3.0 and lower devices will work just like every other Type-C compliant device for every use case except when connected to a QC charger, in which case they behave like a QC device.

You’re probably wondering how we got to the current charging standards mess. I’ll probably explain that in a later post.

†The USB-IF is addressing this.


Author: jdrch

ISTJ, Rice Owl, UF Gator, mechanical engineer. STEM, sports, music, movies, humor. Account mine only & unaffiliated.


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