Windows tablet otg simultaneously charge?

Question

I have a Windows tablet and otg adapter that can simultanously charge the device but there isn't enough current flowing to fight the discharge!? I have 4 usb devices attached to my otg usb hub. Can it be the problem? Could a extra powered usb hub solve my problem? Thid isn't helping me (mostly Android):http://forum.xda-developers.com/showthread.php?t=1822653&page=16. Thanks in advance for any help!

Solution

If you have a hub connected to the tablet, the tablet is in host mode, and must be a SOURCE for VBUS. Therefore it can't charge itself. To accomplish what you want you need a special device called "accessory charge adapter". In simplest form it might look like this:

In theory your tablet should discriminate between ID pin grounded (host mode, sources VBUS), ID pin floated (device mode, consumes VBUS), and ID pin = 100-125k, meaning "accessory charger". In this case the tablet should serve as a host, but consume VBUS for internal charging.

Comments

[Ale..chenski]

In order for people to help you, you need to explain: (a) what is your tablet model, link? (b) which otg adapter? (c) the adapter charges simultaneously what, the "device", and what else? (d) what is "otg usb hub"? (e) Where do you get your power from? Drawing a diagram of what is connected to what and who is charging whom would help a lot.

[Micromega]

I need the otg to charge and serve as an usb hub and fight the discharge with 4 usb devices attached to it.

[Ale..chenski]

Why do you call the hub as "otg hub"? Is there any special feature in your hub?

[Micromega]

Yes, it works but the charge isn't enough. A quick search didn't help. Do you think it is my power supply or could a self-powered USB hub helps? I could also just open and attach an external power source.

[Ale..chenski]

Do you mean that you already have the "accessory charger" provisions as above? Then where do you get the voltage from? I have not seen any "OTG hubs". Normal hubs must be strictly prohibited to back-source anything into VBUS. Unless you have something special, but you don't tell us.

[Micromega]

Yes, I have this ac. It's also a hub with 4 usb 2.0 ports and a micro usb port for the power supply!

[Ale..chenski]

Do you mean you have a wall adapter that feeds the port shown on the bottom of the picture? What rating does it have, 5V and how many Amps? Is sounds very likely that your tablet does not understand the 100k accessory mode.

[Micromega]

I am not so sure. I have 2amps wall adapter with a display. When connected it shows less then a 1amps. But the tablet led is blinking red, Windows tray icon shows charging. It's also chareging when it's off. Thus I think it's the 4 devices or so. I can't really test it because there is an external USB disk drive!?

[Ale..chenski]

You should try to disconnect all your devices from the hub, and see how much charge is going into the tablet. I think the tablet gets confused, and gets charged with some minimal current that is not enough to sustain both functionality and battery charge simultaneously.