I'm developing apps so I have often a mobile device connected sometimes the battery just drains out and I'm wondering why this is happening. I was thinking about why is there no USB hub with Quick Charge. I guess this is caused by a different "USB modus" where a communication with the device is not possible while charging.

I read somewhere that USB 3.1 would allow to charge devices with 100W which is a lot. However I didn't find any reliable source where I could understand how this works. Does that really mean that I can transfer data and charge? If so what kind of certification or feature does the "charger" and "receiver" require? Is that defined in USB-PD?

I would be really happy if someone could enlighten me how charging works internally and where the pitfalls for the manufactures are.

  • Please add some details about your development machine and the mobile devices. Your host USB ports may be limited to give only 100 or 500 mA. I always use a charger of 2 A or more and connect it only for deployment.
    – ott--
    Oct 1, 2016 at 19:42
  • I connect the device with a normal USB 3.0 USB-A port, nothing special at all. I guess it will be charged with the 500mA. Devices which I know that they die over the time would be the Nexus 9 or even a Nexus 6. Directly connected or via powered hub does not change anything. The exact setup does not really matter since I want to know how USB works internally. The point is that I cannot use a charger while debugging or a long running automatized instrument testing.
    – rekire
    Oct 1, 2016 at 19:49
  • Questions about charging mobile devices aren't on-topic.
    – fixer1234
    Oct 2, 2016 at 5:46
  • 1
    My question is about hardware connected with my computer which seems to be on topic on superuser. I read the scope before asking the question.
    – rekire
    Oct 2, 2016 at 6:49
  • 1
    @fixer1234 From the FAQ it matches "computer hardware" which is USB 3.0 and I also checked this point "electronic devices, media players, cell phones or smart phones, except insofar as they interface with your computer", since I want to interface it with my computer it should be fine. Please correct me if I'm wrong.
    – rekire
    Oct 2, 2016 at 15:01

1 Answer 1


All information can be found on www.usb.org.

The rate how fast a device charges itself depends on three factors:

  1. What kind of charger signatures the device can understand, and

  2. What kind of signature a USB port provides.

  3. What is the charging limit for a particular battery embedded into design.

Not long ago the USB ports were meant to adhere to so-called Battery Charging Specification, latest BC1.2. If a port provides this BC1.2 signature, AND the device supports this signature, the charge can be up to 5A. But it usually never happen. And yes, the port can still transfer all USB data. This standard is pretty much dead.

Newer charging protocol uses various pull-ups on a dedicated CC in in Type-C connector, and can deliver up to 5A at 5V. But the device must use Type-C connector to make this determination.

Most recent charging specification is called "Power Delivery v2.0", which uses a serial protocol over the same CC pin. The protocol can negotiate VBUS voltage up to 20V at current up to 5A. First revision of PD tried to communicate the capabilities over VBUS, and now this method is abandoned. This solution is not quite on the market yet, and probably never will be.

For your particular case it is usual that the standard power delivery form a regular port (500mA) is not enough to maintain full-featured functionality of mobile processor and simultaneously charge its battery. So the battery drains out during development/communication process.

Now, the solution to your particular issue depends whether your mobile device is used in host, or in device mode.

If in device mode, there are hubs supporting BC1.2 specification on some USB ports. They should provide sufficient current capabilities IF your device understands BC1.2 protocol. It is likely that your device uses only USB2 port, so it can't understand USB3 capability, and draws only under 500mA.

If your device does not understand BC1.2 protocol, then you are in trouble, since it is the device who decides how much current to take, not the host port.

If your device operates in host mode, the solution is in so-called Accessory Charger Adapter.

  • Thank you for your long answer. That gave me some insides which I missed yet. Could you point out what Quick Charge is in that "USB universe"? About the host mode and that charger adapter, that is just for the case when I plug in a flash drive for example right? When I plug it in a computer the mobile device is in the client mode?
    – rekire
    Oct 2, 2016 at 14:57
  • "Quick Charge" is another proprietary attempt to have an elevated voltage (5V, 9V, 12V) from a Quick-charge-enabled Power Supply, similar to the official Power Delivery idea, while using same USB connectors. Just like I heard that Apple is abandoning their proprietary Lightening connector, I guess the Qualcomm invention will die too. Both PD and QuickCharge will likely die before gaining any market, and replaced with wireless inductive chargers. Oct 2, 2016 at 15:37
  • Regarding "accessory charging" when the mobile device is in host mode (as you said, when flash drive is needed), see this topic, superuser.com/questions/1124237/… Oct 2, 2016 at 16:18

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