[Gta04-owner] [PATCH] twl4030_charger: add software controlled linear charging mode.

Andreas Kemnade andreas at kemnade.info
Tue Jun 11 18:48:01 CEST 2013


On Tue, 2013-06-11 at 16:14 +0200, Rico Rommel wrote: 
> Am Samstag, 8. Juni 2013, 18:36:16 schrieb Andreas Kemnade:
> > Note: If linear charging mode is used there should be some method of
> > stopping charging automatically. It is not a so time-critical, but
> > it is the wrong setting for leaving a charger connected for several days
> > since Lithium batteries should not be kept at 100% for longer periods.
> > Linear charging does a good job with not so reliable power sources, since
> > several voltage controlling is then often too intelligent.
> > It was used with a bike hub dynamo since a year or so. In that case there
> > are automatically charging stops when the cyclist needs a break.
> > Signed-off-by: Andreas Kemnade <andreas at kemnade.info>
> I have read the text several times but still don't understand it.
> What is linear charging and what is the difference to "normal" charging?
well, linear charging is not a usual word the contrary is some other
weird charging mode which we cannot use (which is not linear, some kind
of pulsed one).
The basics of lithium charging are:
charge with a low current until a defined voltage (<3V) (precharge is
that in the TRM called)
charge, limited by current and voltage, that means first it is limited
by current and then by voltage

That is what is done by most cheap chargers and is also done in this
linear charging mode.

Then you add some more safety stuff to it and you have the standard
automatic charging which does that without any software needs.
- end of charge detection by a low current threshold (you should not
even keep Lithium cells at 100%)
- Vbus monitoring: unplug detection, OTG stuff
- various timeouts (if not full after x minutes, ..., restart charging
if vbat < 3.9V and charger connected)

Under some circumstances, these additional things cause trouble. With
that software-controlled linear charging, you can do the items  on the
second list by yourself. 

Andreas Kemnade

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