GSENSOR_3V3 voltage drop

Christoph Mair ml at
Sun Aug 23 20:39:53 CEST 2009

> [Álvaro Lopes So  23. August 2009]:
> > Christoph Mair wrote:
> > > Hello,
> > > 
> > > I have some questions regarding the GSENSOR_3V3 line:
> > > Under normal conditions I measured 2.8V. 
> We need to check what's the correct setting for LDO1 voltage, in PMU.
> 2.8 sounds fishy.
FIxed with kernel patch. Now i get ~3.4V which seems to be ok.

> > > In suspend, the voltage drops to  
> > > 2.4V. I thought the the line would carry 3.3V when powered on and ~0V in 
> > > suspend. Why isn't that the case?
> ACK.
> For suspend I suspect a reverse feed thru SPI_MOSI1 and/or SPI_CLK1 lines 
> which might be at high (1) level even though LDO1 is powered down. If that's 
> the case then it needs a fix urgently. Some of he kernel guys need to check 
> that.
> Another more unlikely scenario is suspend reprograms LDO1 out voltage to 
> Even more unlikely seems you overload the powerrail (>50mA) during suspend 
> only.


> > Suspend is also defined by software. Typically this would be set to GPIO1 
> input, which is controlled by CPU (PWREN signal). Maybe someone can confirm 
> this.
> I'm not completely convinced about that. Alas we have no generic application 
> notes for GTA02-hw, so you can only guess what's the supposed way to manage 
> things. My guess however would be to switch LDO1 down directly via 
> PMU-register by writing over I2C. The purpose of PWNEN is a little bit
> cloudy to me.
There is some communication on the I2C bus approx. 13ms before the voltage 
drop. The last message starts with:
11100110<ACK>00000111<ACK>10110011<ACK>11111101<ACK> ..
0x6E, 0x07, 0xB3, 0xFD ..
And is therefore addressed to the PMU. I can try to decode the rest, if it may 
be useful.
(The actual decoding was done in my head, so there may be some bit errors ;) )

> > This line powers two LIS302DL accelerometers, which draw 0.4mA max each. 
> This gives less than 1mA. This gives enough room for power output, so either 
> your
> > problem lies in VB_SYS (not enough current to feed the LDOs),
> unlikely, FR wouldn't work at all of that was the case I guess.
> > a shortened caps (C1718), broken LIS203DL... 
> hmm, doesn't make a good story with the whole bunch of observed strange 
> behaviour
> > 
> > What voltage do you see in VB_SYS, on those scenarios ? Can you also check 
> voltahe PMU GPIO1 pin (TP1740) when phone is in suspend mode ?

I will check the voltage at TP1704 now.

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