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

Werner Almesberger werner at openmoko.org
Mon Jun 22 14:13:48 CEST 2009

?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.

- IO_1V8 comes from a step-down converter, which is more efficient
  than an LDO. So if GPS draws a significant current on its 1.8 V
  rail, that may make a difference.

Ideally, someone with a bit of spare time on their hands would measure
GPS performance and power consumption on a GTA02, then rework it to
use IO_1V8 instead of the internal LDO, and then measure again, and
also check what happens if RF_3V is cut.

- Werner

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