ADK Power query

Hi

I'm using an asus transformer tablet with an ADK board and everything is working well apart from the powering of the tablet. The ADK board isn't capable of supplying of enough current to keep the battery charged. I would like to separate the power supplies so that the tablet is supplied via its own original charger and the ADK is powered by a separate 9v supply. I bought a USB Y cable which has 2 USB A plugs and 1 USB A socket but this doesn't work as the tablet no longer sees the ADK board.

Any ideas of how to connect this ? I have USB connectors and could make a custom cable if required

Cheers

Paul

Hi

I have found the Battery Charging specification for USB devices and I think what I need is an “Accessory Charger Adapter” mentioned on page 38.
Does anyone know if one exists? I couldn’t find any on-line. If they don’t exist would it be possible to make something from the information in this document?

Cheers

Paul

batt_charging_1_1_FINAL.pdf (389 KB)

Hi

Does the USB Controller on the ADK limit the current to 750mA? In my set-up I'm not using the on board power for " any actuators and sensors attached to the board" so couldn't the whole 1500mA be made available to the tablet for charging?

“Because the ADK is a USB Host, the phone will attempt to draw power from it when it needs to charge. When the ADK is powered over USB, 500mA total is available for the phone and board.The external power regulator can supply up to 1500mA. 750mA is available for the phone and ADK board. An additional 750mA is allocated for any actuators and sensors attached to the board. A power supply must be capable of providing 1.5A to use this much current.
The board can operate on an external supply of 5.5 to 16 volts. If supplied with less than 7V, however, the 5V pin may supply less than five volts and the board may be unstable. If using more than 12V, the voltage regulator may overheat and damage the board. The recommended range is 7 to 12 volts.”

http://arduino.cc/en/Main/ArduinoBoardADK

Hi AmbiLobe

Thanks for the reply , but I think you have missed the point of my question.
I want to know if the usb controller on the ADK is the limiting factor? Is there a 750mA limit set in the firmware in this micro?
If it is set in the firmware for the usb controller could it be changed to allow 1500mA to be available for charging of the device?

Cheers

Paul

I have now resolved the problem I was having. As far as I can tell the max charging current for a phone/tablet connected to the ADK is limited by IC2 (LM2736Y) to 750mA.

However the problem I was having is caused by the ASUS tablet not using a standard 4 pin usb cable see here for more info http://www.transformerforums.com/forum/asus-transformer-tf101-help/12490-alternative-usb-based-charging-methods-tf101-besides-using-asus-supplied-charger.html

Basically the ASUS tablets use an extra 15v pin in the original chargers to charge the tablet at a much higher rate. I have now made a Y cable to suit and can confirm it works well.

Paul