GSENSOR_3V3 voltage drop
joerg at openmoko.org
Sun Aug 23 22:30:48 CEST 2009
[Christoph Mair So 23. August 2009]:
> > 2009/8/23 Christoph Mair <ml at chonyota.net>:
> > > The voltage is now between 3.32V and 3.44V which seems to be ok,
> > Nice.
> > > but after
> > > suspending it still drops to 2.44V Vmax and 1.78V Vmin (when the compass
> > > starts a measurement).
> > Just to make sure I got you right: You enable the "g-sensor" and get about
> > then you suspend and _while suspended_ you get 2.4V and 1.8V respectively?
> > What happens when you resume? Do you get back 3.3V? If this is the case
> > probably don't set GPD12/13 (CS), GPG7 (CLK), GPG6 (MOSI) to 0 and GPG5
> > to pulldown during suspend and leak the voltage from the CPU. Can you
> > make sure you set those pins during suspend!
> I switch my Neo on, and the line goes immediately to 3.3V (I'm using Qi, if
> that matters). After SHR started (but with andy-tracking-kernel) I take the
> first measurement which results in 3.3V. I never explicitely enabled the g-
> sensor. Then I suspend the device which results in the voltage drop down to
> 2.4 (normally) or 1.8 (only if my chip draws some current, I think 1mA max,
> but I did not check this yet).
> Right after resuming the voltage rises to 3.3V again.
> I never touch the other pins since the compass chip has a I²C interface. I
> just use GSENSOR_3V3 as power supply, because it is easily accessible at
As suspected in my other posting, and explained by Sven, the GSENSOR_3V3 rail
may see "phantom"-feeding by the data(MOSI)/clk-lines if those are at 3V3
while LDO in PMU is powered down, during suspend. It doesn't matter if *you*
touch those lines, the feeding may take a path thru the gmeters (the clamp
diodes there) so you see some voltage of 3V3 - (voltage-drop on diode).
Please check as suggested by Sven
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