I am doing some research around a portable device powered with a Li-ion sin=
gle=20
cell 750-900mAh rechargable battery. At this stage I am planning for a 1450=
0=20
size battery with built in protection. The charger circuit will handle over=
=20
voltage/charging protection but the cell itself will handle under voltage=20
protection and it is a size that will fit in a standard AA holder. The devi=
ce=20
will be connected to a PC via USB and will normally also be charged through=
 the=20
USB port.

I am planning to handle charging like this: When the unit gets connected to=
 the=20
PC via an USB-port it is also powered from here. At this point the charger =
is=20
not yet operating and the ucontroller will politely ask the USB host for hi=
gh=20
current (500mA). If granted the charger will be set for 350-400mA. If not I=
=20
will asume that there is only 100mA available and will charge at around 60-=
80mA=20
(a little depending on how much I will need for the rest of the circuit).

Now, I am wondering how to handle charging if it is connected to a stand al=
one=20
charger with a USB cable. This will not be able to communicate with the mic=
ro.=20
Does the fact that it can not communicate tell me to start high current=20
charging? How is this normally handled in phones for example? Does these US=
B=20
chargers tell the capabilities to the portable device in another way, e.g.=
=20
pullup/pulldown resistors on the D+/D- lines?=20


/Ruben

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
Ruben J=F6nsson
AB Liros Electronic
Box 9124
200 39 Malm=F6 Sweden
www.liros.se
Tel +46 40142078
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D

--=20
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