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I have an Android tablet and an external device that gets plugged into its microUSB port. This device is powered by the tablet through that port.

If I plug in a cable that has a single male and two female ports as shown below, would I be able to plug in an external power supply (5V, 2A) to both charge the tablet and power the external device at the same time?

enter image description here

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    This way of connecting USB Micro Port is to my knowledge far outside of the USB [OTG] specification, so if it works as expected (tablet charges) or not depends on the USB chip in the tablet. Usually when in OTG the tablet would be responsible for providing power so connecting a second power source to the same cable can cause problems with unforseen side effects.
    – Robert
    Nov 10 at 19:05
  • Thanks for mentioning the term "OTG", that led to some investigation. It is actually possible to have a host device also be charged, but likely requires a hardware modification of soldering a resistor of a certain value between pins 4 (ID pin) and 5 (ground pin). I'll post an answer / findings once I've had more time to gather the information, assuming no one else did it first.
    – plu
    Nov 13 at 18:39

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From looking further into the contents of this post, yes, that is technically possible, but likely has to be done as a DIY solution given it requires:

  1. the tablet itself to have the correct hardware
  2. following the standards of something called an "Accessory Charger Adaptor" (ACA) which is not commonly available as something that can be easily purchased. **.

**For example I found just one product that's the closest match to what I'm looking for.


Looking into the "BC1.2_without errata 2010-12-7" document of the "Battery Charging v1.2 Spec and Adopters Agreement", it tells us the ACA can have three ID resistances, one of which allows connection while charging ("RID_C" of somewhere between 36 and 37 k-ohms).

If that resistance is pulled up to the VBUS power line, and if there exists an ID comparator connected to the ID pin on the tablet side, then that would be one of the minimum requirements for it to work.

enter image description here

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