I am designing a "smart charger" for my personal Android phone. I would like it to be able to adjust the amount of (or turn off) power going to the phone.

Planned Implementation:

The "smart" features would be implemented on the phone, and all communications handled by a device such as the MAX3421E (Ie. Android ADK).

Here's a block diagram: Block Diagram


What is the proper way to communicate with the phone so that the phone's charge circuitry takes as much power as possible (Is this even possible with the Maxim chip)?


10 to 1, your phone uses some variation of the USB Battery Charging standard. That is to say, by changing what the phone sees on the usb D+ and D- pins, it changes ho it should charge. Connecting D+ to D- (shorting them together) indicates high speed charging. Connecting them to ground is another, as is leaving them floating (dumb charger) which indicates 500mA draw only.

It can also respond to the Appl standard, where a resistor voltage divider from VUSB to D+ or D- to ground creates a specific voltage on the d+ and d- line, indicating 1.0A charger, or 2.1A charger.

But the Android ADK is an active USB host, like a computer. The usb data lines are in active use. This prevents the phone from seeing the line as a charger, so you can't do any of that.

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