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Can you charge & USB Host mode simultaneously?

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OP mvmacd

mvmacd

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Posted 20 July 2012 - 12:37 PM #1

I wanna get a Nexus tablet, but I'm afraid that I won't be able to access my USB hdd and charge the device at the same time. Can someone confirm if it's possible? I asked over at xda forums, but I didn't get a solution.

could I perhaps use a USB OTG cable and a Y-cable with a USB charger? or even if I had to get a usb hub, I would, I just need to get some clarity.
Thanks!
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sfreemanoh

sfreemanoh

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Posted 20 July 2012 - 01:18 PM #2

I doubt it. However, the battery life on this thing is really pretty good. From Tuesday around 5PM until mid Thursday, I used it for maybe 3 hours of screen-on time and had it unplugged the entire time. I watched some Youtube, flashed some a couple ROM's, blah blah blah, and the battery was around 65%.
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OP mvmacd

mvmacd

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Posted 20 July 2012 - 09:49 PM #3

Hmm.. Well, if it's impossible, is it hardware or software limitation?

Picture this, i plug in a powered USB hub, into the otg cable, except I cut out the 5v wires before it reaches the hub, then apply my own 5v from a separate charger. Would it charge upon receiving the voltage? Or would it ignore it cuz its in host mode?

Pardon the grammar I'm on my phone
Thx
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OP mvmacd

mvmacd

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Posted 22 July 2012 - 08:27 PM #4

bump.
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OP mvmacd

mvmacd

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Posted 31 July 2012 - 03:21 PM #5

another bump
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AlexanderT

AlexanderT

Average Android

Posted 01 August 2012 - 12:15 PM #6

I don't think it would ignore the charge if it has enough power getting to it.
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packruler

packruler

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Posted 01 August 2012 - 07:28 PM #7

FYI http://www.ti.com/li...ao5/slusao5.pdf
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I like to think I know what I'm talking about don't burst my bubble

dansan

dansan

Android Apprentice

Posted 02 August 2012 - 10:23 AM #8

FYI http://www.ti.com/li...ao5/slusao5.pdf


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spbogie

spbogie

Average Android

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Posted 03 August 2012 - 10:34 AM #9

Assuming that is the charge controller used in the n7...

Short Answer: No

Long Answer: When the device detects that it has entered USB Host Mode (OTG) the charge controller switches from charge mode to boost mode. In effect it reverses the charge circuitry (not exactly, but close enough for this explanation) so that instead of charging the battery it draws power from the battery to power whatever device is connected. When in Boost mode, the controller will not charge the battery from the VBUS (USB) input. In theory, there are 2 ways in which host mode + charging could be accomplished. Method 1 (Hardware): The charge controller has an additional VIN connection intended for use with an AC adapter which should be able to continue charging the battery even when VBUS is in Boost mode. However, given the WCSP package (Surface mount connections under the chip itself, no exposed pins) this chip uses, connecting to this pin would be virtually impossible if it is not broken out somewhere on the circuit board. Method 2 (Software): The controller has an I2C interface used to control its operation. This interface should be connected and being controlled by a kernel driver. If this driver is accessible, it should be possible to tell the charge controller not to enter Boost mode, and thus allow charging to continue while the USB interface is in host mode. This would allow charging, but also require an external source to power any attached usb devices. Note, this is all heavily dependent on the assumptions of the charge controller being used, and configuration it is in. In other words, Maybe...
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dcplaya

dcplaya

Android Beginner

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Posted 03 August 2012 - 11:33 AM #10

Assuming that is the charge controller used in the n7...

Short Answer: No

Long Answer: When the device detects that it has entered USB Host Mode (OTG) the charge controller switches from charge mode to boost mode. In effect it reverses the charge circuitry (not exactly, but close enough for this explanation) so that instead of charging the battery it draws power from the battery to power whatever device is connected. When in Boost mode, the controller will not charge the battery from the VBUS (USB) input. In theory, there are 2 ways in which host mode + charging could be accomplished. Method 1 (Hardware): The charge controller has an additional VIN connection intended for use with an AC adapter which should be able to continue charging the battery even when VBUS is in Boost mode. However, given the WCSP package (Surface mount connections under the chip itself, no exposed pins) this chip uses, connecting to this pin would be virtually impossible if it is not broken out somewhere on the circuit board. Method 2 (Software): The controller has an I2C interface used to control its operation. This interface should be connected and being controlled by a kernel driver. If this driver is accessible, it should be possible to tell the charge controller not to enter Boost mode, and thus allow charging to continue while the USB interface is in host mode. This would allow charging, but also require an external source to power any attached usb devices. Note, this is all heavily dependent on the assumptions of the charge controller being used, and configuration it is in. In other words, Maybe...


I havent looked at that spec sheet but I just went over the USB OTG spec and the spec has details on how to get it to work. Charging the A-Device while connecting to the B-device is possible with a resistance between the ID pin and ground as well as power. Both devices get power from the charger. There is just no SRP support but also isnt needed since "VBUS is already asserted at both the OTG Port and Accessory Port."
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