[gta02-core] Calypso's last dance

Dave Ball openmoko at underhand.org
Mon Jul 27 02:21:15 CEST 2009

Werner Almesberger wrote:
> Alvaro Lopes wrote:
>> [I'm investigating how to get those 3A peak
>> without disturbing the PMU too much, in case we go after option's chip]
> I think something like the current arrangement, with going directly
> to the battery and without the PMU knowing any of this, is be the
> canonical way to solve this.
> This means that the PMU will have misleading information about battery
> current and even charging state, but this seems unavoidable.
> Thinking about it ... there might actually be a possibility to do
> better. If we tapped into Vsys instead of Vbat, the PMU would know
> what we're doing. This would limit the available current to 2.2 A
> (50633 manual, table 91, Ilim(BAT-SYS)), so either some buffering
> would be needed for the peaks, or an external "ideal diode" from
> Vbat to Vsys to boost the one inside the PMU (figure 38).

It might be slim, but there is the possibility that the 3A peaks only 
occur in certain conditions that we can design not to hit.  As an 
example, it might be a sensible design compromise to only use 3G in a 
low-power mode, if one is available and that makes integrating a calypso 
replacement easier.  Or if we decide we're not using the diversity 
reciever or other elements of the chip, there should be some impact on 
power consumption.

Always good to explore the options though (no pun intended)


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