I'm really surprised no one has referenced this yet, but there *is* an
official USB dedicated charger and detection method specification:

http://www.usb.org/developers/devclass_docs

(see Battery Charging section)

Almost every commercial high volume USB device I've seen manufactured in
the last 2 or 3 years has been "charge-only" adapter aware in one way or
another.

A lot of device ports have the "charger only" connection detection circuits
built-in now (think SOCs used by smart phones, etc.). If not, the units
I've looked at roll their own. Regardless, the conditions for detecting an
external "charger only" connection are clearly spelled out in the above
specification. Also note that the specification covers input voltage ranges
and other pertinent details.

Matt Pobursky
Maximum Performance Systems

On Fri, 10 Dec 2010 03:58:34 +1300, RussellMc wrote:
>> A question: Since the data lines have to be set at a certain voltage
>> (with resistor voltage dividers), and the battery pack voltage will
>> vary between 4.4 - 5.6 volts, how would I get a steady voltage on the
>> data lines to tell the iPhone to draw 1 Amp? Would I need to just stick
>> a low power voltage regulator at around 3.0 or 3.3 volts and create a
>> divider from there?
>>
>
> Consider:
>
> -Read the article/s referenced here (by me and others) that told what
> they did and provided circuits.
>
> - Do what they did.
>
>
> Russell

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