[gta02-core] GTA02 GPS chip (ATR0635) VDD 1.8 power rail

Rene Harder rehar at saweb.de
Mon Jun 22 17:22:49 CEST 2009

Werner Almesberger wrote:
> ?lvaro Lopes wrote:
>> * Why was this chosen over PMU 1.8 power rail (IO_1V8) (or the other
>> way around) ?
> I could see the following consequences of connecting GPS to IO_1V8:
> - this may create an EMI path, so at least a bead should be there.
>   (I.e., instead of R7601)
> - IO_1V8 stays on in suspend while RF_3V (VDDIO, VCCx, VBP) can be
>   cut. Not sure if this is an operating condition the ATR0635 would
>   be happy in.

I see a big problem with shutting down the RF_3V, we'll shutdown the
VBAT as well. That means no SRAM and backup RTC. Without backup RTC
we'll increase the start up time.

The good news is we do not need to shutdown RF_3V because if you bring
the GPS chip into standby mode, NSHDN connected to LDO_EN will go down
and will shutdown the internal 1.8V LDO as well.

One of the more important questions is, if you shutdown the chip by
software, does the core shutdown as well or is it still running if
VDD1.8V is active.
I'm not sure but i guess it will only go into sleep mode where it still
needs more power than in shutdown mode.


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