GTA02 USB and battery current profile

[Felipe Balbi]

On Sat, Mar 08, 2008 at 08:11:12PM -0300, Werner Almesberger wrote:
> 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).

It doesn't depend only on usb power constraints, it has more to do with
your pm chip.

I had a device that could charge with up to 1A if connected to a
dedicated charger, although we can charge with up to 2.5A in that
situation.

-- 
Best Regards,

Felipe Balbi
me at felipebalbi.com
http://blog.felipebalbi.com