GTA02 USB and battery current profile

joerg joerg.twinklephone at gmx.de
Sun Mar 9 02:29:49 CET 2008


Am So  9. März 2008 schrieb Werner Almesberger:
> In order to better understand what's happening with our power management,
> I profiled USB and battery current during the boot process:
> 
> http://people.openmoko.org/werner/usb-batt.html
> 
> (USB on top, battery below.)
> 
> This is GTA02v5 without SIM card running roughly the daily build from
> about one week ago.  At the end, I let the system sit still for a moment
> so that it would begin to charge the battery, then I logged in with SSH
> and suspended it.
> 
> Negative battery current means that we're charging, positive that we're
> discharging. The unloaded (simulated) battery voltage is 3.6V throughout
> all this. (Inner resistance is ~600mOhm - about twice than a real
> battery.)
> 
> The x axis counts samples. Note that one of the two meters is a bit
> slower than the other. The y axis shows amperes. Integration time is
> 4ms, so we'll miss any really fast transients.
> 
> What's interesting here is that we only draw a maximum of about 290mA
> from USB, which is quite conservative (that is, if we're cleared to get
> 500mA).

Yep, this is either 190mA too much, or 210mA low. It seems there is quite some 
setting that needs to be tuned in 50633. The setting for max usb current is 
neither 100mA nor 500mA, max charge current seems like someone should check 
it, and it's not very clear whether this CV or CC mode for charging.
Even when we assume the registers of 50633 to be set at a very late point 
during boot, the end of the plot still doesn't look better than the 
beginning.

jOERG




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