USB current limit when phone off
cedric.berger74 at gmail.com
Thu Feb 5 09:24:20 CET 2009
I was surprised about the current used by my freerunner when off, from
a dumb USB charger, that seems to have been more than 100mA.
I have yet to do more tests because I am not really sure how much
power was drawn...
My car charger has got a led that looks (I am not sure about how it is
designed to work !) to be :
- green when nothing is draining power (unplugged or my when my phone is off).
- amber when little current is drawn (my phone plugged in, on, and
using about 100mA -so when nothing special done, and battery current
reported by phone confirmed usb current was indeed about 100mA-)
- red if more current is drawn (about 500mA, forced via
usb_chage_limit_dangerous -battery charge current confirmed it was
using about 500mA-)
I wanted to charge my phone :
- if plugged when off (ex. pulling bat to shutdown since plugging usb
starts the phone...), led was green : no current. ok (that's sad but
- starting phone : led amber, from beginning to even after end of boot
(ok. 100mA as expected)
- NOR uboot : led amber... 100mA ok.
- off after NOR uboot (menu "off") -> green, no current. (I used to
use this uboot off to have phone off with 100mA charge, but was with
- from Android (so was using 100mA from charger) : shutdown..... and
led went red ! (sometimes turned to amber for about one minute, then
back to red). Battery charge went from 13% to 36% in about 30 minutes,
so looks like it was indeed more than 100mA (?)
=> So it looks like shutting down from Android (where I did not force
higher current), I could get in a forbidden state where USB current
was more than 100mA ?!
(well it was good for me since I wanted to charge my phone, but anormal...)
It was with Qi from a few days ago, and Michaels Trimarchi kernel v10
(most recent one).
I did not test yet with another distro.
Of course I have not much real current measuments, and am not sure
either that my charger have not some resistance that could have made
the phone believe it was the wall charger... (but usually, if I do not
force it, it never uses more than 100mA)
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