GSENSOR_3V3 voltage drop

Álvaro Lopes alvieboy at
Sun Aug 23 15:27:08 CEST 2009

Christoph Mair wrote:
> Hello,
> I have some questions regarding the GSENSOR_3V3 line:
> Under normal conditions I measured 2.8V. 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?
> How much current should I be able to get from this line? I connected the 
> three-axis magnetometer HMC5843 which works fine when the phone is powered on. 
> It even takes measurements in suspend, but then the voltage drops down to 
> 1.76V when a measurement takes place (every second for 4ms).
> Can someone explain how this is supposed to work?

Hi Chris,

Although I'm not directly involved in GTA02, I am in gta02-core, and I might be able to answer some of your questions.

GSENSOR_3V3 is generated from one of PMU LDO (LDO1). Output voltage is controlled by software, in 100mV increments. Max. output current from this LDO is 50mA.

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.

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), a shortened caps (C1718), broken LIS203DL...

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 ?



> Thank you,
>   Christoph
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