[gta02-core] USB schematics

[Rene Harder]

Werner Almesberger wrote:
> 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 ?
>   

A cap would make sense for decoupling the USB_VBUS line, well a varistor
has a capacitance as well but this one is quite small. ;-)

>   
>> 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.
>   
No, I mean if you click on a varistor you'll get the full description.
In the description it's a 2.4V varistor which is wrong.
> 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
>
>