I think it is basically an industry-adopted hack.  If the pullups from=20
D+/D- to the USB +5V are certain values, it means the device "requests"=20
(or maybe just says "I know what I'm doing" for) an increased max=20
current, so please mr. USB host, don't cut me off as a Bad Device when I=20
pull 1amp or 2...

I'm sure there is a wiki somewhere about all this tomfoolery.  It does=20
make it confusing to users, and I have USB cables that don't work for=20
data that of course look just like regular ones.  Makes debugging USB=20
devices all that much more hair-pulling.

With the size of batteries in smartphones and in particular tablets 1amp=20
or even 2amp @ 5V is still under 1C going into the battery...

J


Ryan O'Connor wrote:
> But surely charger circuits inside phones have current limiting for
> the charging cycle? So it wouldn't make a difference...
>
--=20
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