[gta02-core] USB schematics

Werner Almesberger werner at openmoko.org
Sat Jun 20 21:56:23 CEST 2009

Rene Harder wrote:
> The reference of some varistors start with C instead of D.

This appears to be a mistake. Maybe somone was fooled by seeing
the capacitance being specified in the BOM.

> Maybe there supposed to be capacitors, which actually would make sense.

Hmm, do you think we need more ?

> There are 3 varistors on the USB_VBUS line 2 of them labeled with C.
> Anyone an idea, why there are 3, I think one would be more than enough.

Hah, now that you mention it ... C4902 and C4909 do indeed look
rather useless. In GTA01, we had only one as well.

> There is an error in the om schematics, the varistors connected to the
> USB power line have an allowed dc operating voltage of 5.6V (data sheet)
> instead of 2.4V (om schematics).

Hmm, you mean the 2.4 V mentioned in the box above ? I think that's
a reference to VISA, which is 2.4 V.

With Rext -> oo, Vadc (sp!) would be VISA/(R1731+R1732)*R1731 = 1.73 V,
which is somewhat close to the 1.85 V mentioned in the box.

> Also om is using capitalized SI prefixes e.g. kilo=K, nano=N. That might
> cause confusion if you have milli=M and Mega=M. I think it's better to
> stay with the official captions  kilo=k, nano=n, mega=M etc.

Yesh, I like that better as well. It's not very likely to cause
confusion, but there might be the occasional 100 mOhm trace or
such ...

- Werner

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