[gta02-core] ECN0044: Current rating of backlight LED inductor (L1704)

[Werner Almesberger]

We have a new ECN: the inductor (L1704) of the boost converter feeding
the backlight LED has an odd specification that makes it hard to source.

We can either lower the current rating (see the ECN for why this should
be okay) or increase the footprint (which would also lower the
resistance and save a bit of power.)

I've tentatively changed the current rating of L1704 to 600 mA to let
the BOM system pick up a suitable part.

Further details in
http://svn.openmoko.org/trunk/gta02-core/docs/ecn/ecn0044.txt

Comments ?


By the way, the BOM system now supports not component parameters
that are identical to some specified value but also parameters
that are below or above some value. E.g., one can now specify the
voltage rating of a capacitor as 20 V and the BOM system will
automatically pick a 25 V part, if available.

The rules for this are defined in gta02-core.sub E.g., in the
above example, C1764 has a parameter "V" with a value of 20V.
This gets translated by the rule  FN=*V -> V=>=$FN  to V=>=20V,
which in turn matches the V=25V of
TAIYO-YUDEN TMK316BJ106KL T=C   M=X5R   C=10uF  TOL=10% V=25V   FP=1206

This is much cleaner than relying on footprint sizes to force
selection of parts with the right parameters.

- Werner