Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the usb gadget power negotation

[Pavel Machek <pavel@ucw.cz>]

Hi!

> > That's not actually 100% clear to me - for what the wm831x is doing it
> > probably *does* want the higher limit.  This is a system inflow limit
> > (as it should be for this), at least the charger will adapt to voltage
> > variations though other users in the system are much less likely to do
> > so.
> 
> Interesting ... I hadn't considered that possibility.
> 
> As long as the current remains below the maximum, the charger will
> reduce the voltage towards 2V as load increases.  Somewhere before it
> gets there, the system will not be able to make use of the power as the
> voltage will be too low to be usable. So that will naturally limit the
> current being drawn.
> 
> Not having very much electrical engineering background, I cannot say for
> sure what will happen, but it seems likely that once the voltage drops
> much below 4.75V, the charger won't be operating at peak efficiency,
> which would be a waste.
> I can easily imagine that the hardware would switch off at some voltage
> level, rather than just making do with what is there.
> So I'm skeptical of this approach, but I'm open to being corrected by
> someone more knowledgeable than I.

Devices I seen charge down to ~4.2V. This is useful thing to play
with:

dx.com: 406496
1" USB Current & Voltage Detector Tester Meter w/ Red LED Display -
Blue

Best regards,
								Pavel

-- 
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