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From: Bob Myers on 17 May 2010 17:25
On 5/17/2010 2:14 PM, aleksa wrote:
> "George Herold"<ggherold(a)gmail.com> wrote in message news:fa2a60df-7a8a-45b0-943a-d5da4e5b4594(a)s41g2000vba.googlegroups.com...
> On May 17, 3:35 am, "aleksa"<aleks...(a)gmail.com> wrote:
>
>>> If I now adjust my VCC tracks to 50mils,
>>> is there any chance of some problems?
>>>
>
>> Problems, there always seems to be problems. Wider traces may or may
>> not cure your problems.
>>
> I didn't say I *have* problems, I asked
> if widening a VCC *may make* problems.
>

Simple answer: no, not unless there are other things wrong with
the design. Having both Vcc and ground on full planes is the norm
for 4-layer-and-up boards, you know.

> The guy who suggested I should use 25mil VCC
> had an old board, with DIPs, with thick GND
> and thick VCC lines (some 100mils), with caps on
> all chips, but the board didn't work correctly.
> After he had removed the thick VCC line from
> one of the chips, and soldered a thin wire,
> the board worked correctly.
>

And at that point, SOMEONE should've thought long and
hard about just why that should be.

Bob M.

From: aleksa on 17 May 2010 18:34
Thanks


From: Tim Wescott on 17 May 2010 18:36
aleksa wrote:
> "Tim Wescott" <tim(a)seemywebsite.now> wrote in message news:UNmdnem-7tvm7WzWnZ2dnUVZ_tIAAAAA(a)web-ster.com...
>> aleksa wrote:
>>> When I started designing PCBs, I was given an advice
>>> to route GND with 50mils and VCC with 25mils.
>>>
>>> But now I read on the net that VCC should be wide, also.
>>>
>>> I make two-layer digital boards only.
>>>
>>> If I now adjust my VCC tracks to 50mils,
>>> is there any chance of some problems?
>>>
>>> And should I adjust? All prior boards work...
>>>
>>> Maybe I should note that all my previous boards
>>> were built around discreet chips, GALs, SRAM and Z80,
>>> but am now moving towards 180 MHz ARM and FPGA.
>> I need a rope to hold up a sack containing all my belongings. How thick should it be?
>>
>> What? You want to know how many belongings I have, and how much they weigh, and whether any of them are alive and may make the
>> sack bounce and jump around? Why oh why would you want to know that, just to tell me how big a cruddy rope needs to be?
>>
>> OK: I'll make a deal with you:
>>
>> _You_ tell _us_ enough about what you're doing (expected current draw, more about the parts that you're going to use, whether
>> you're running any analog parts, etc.) Then maybe _we_ will have enough information to tell _you_ the answer that you need.
>>
>> And I'll go figure out that damn rope size myself.
>
> Perhaps you can hang yourself with it?

Perhaps I could comment that there _are_ stupid questions? Stupid
questions of the first sort are ones that you already know the answer
to. Stupid questions of the second sort are the ones that are poorly asked.

I'm sorry I tried to help -- I'll remember your level of gratitude if
I'm tempted to help you in the future.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
From: George Herold on 17 May 2010 21:49
On May 17, 4:14 pm, "aleksa" <aleks...(a)gmail.com> wrote:
> "George Herold" <ggher...(a)gmail.com> wrote in messagenews:fa2a60df-7a8a-45b0-943a-d5da4e5b4594(a)s41g2000vba.googlegroups.com...
>
> On May 17, 3:35 am, "aleksa" <aleks...(a)gmail.com> wrote:
>
> >> If I now adjust my VCC tracks to 50mils,
> >> is there any chance of some problems?
> >Problems, there always seems to be problems.  Wider traces may or may
> >not cure your problems.
>
> I didn't say I *have* problems, I asked
> if widening a VCC *may make* problems.
>
> The guy who suggested I should use 25mil VCC
> had an old board, with DIPs, with thick GND
> and thick VCC lines (some 100mils), with caps on
> all chips, but the board didn't work correctly.
> After he had removed the thick VCC line from
> one of the chips, and soldered a thin wire,
> the board worked correctly.
>
> He also said something like "If VCC lines are
> not thick, device will draw spike current from caps,
> rather than the VCC line". Something like that.
> I'm no expert, and I also have to translate it to English...
>
"> Anyway, I'll rephrase the question:
> can widening a VCC line make problems?"

No that makes no sense at all.... some weird time delay thing maybe.
If you do something to your circuit and it responds in a way you don't
understand, then spend some time to understand it, else it will come
and 'bite' you in the future.

Above 100 MHz it's harder... what's the wavelength at 100MHz? (in your
circuit board)
If you are 1/10 of that distance 'strange' things can start to happen.

Tim Wescott probably knows a lot more about electronics than I do....
If you're nice he might help you.

George H.


From: John Larkin on 17 May 2010 23:33
On Mon, 17 May 2010 15:36:36 -0700, Tim Wescott <tim(a)seemywebsite.now>
wrote:

>aleksa wrote:
>> "Tim Wescott" <tim(a)seemywebsite.now> wrote in message news:UNmdnem-7tvm7WzWnZ2dnUVZ_tIAAAAA(a)web-ster.com...
>>> aleksa wrote:
>>>> When I started designing PCBs, I was given an advice
>>>> to route GND with 50mils and VCC with 25mils.
>>>>
>>>> But now I read on the net that VCC should be wide, also.
>>>>
>>>> I make two-layer digital boards only.
>>>>
>>>> If I now adjust my VCC tracks to 50mils,
>>>> is there any chance of some problems?
>>>>
>>>> And should I adjust? All prior boards work...
>>>>
>>>> Maybe I should note that all my previous boards
>>>> were built around discreet chips, GALs, SRAM and Z80,
>>>> but am now moving towards 180 MHz ARM and FPGA.
>>> I need a rope to hold up a sack containing all my belongings. How thick should it be?
>>>
>>> What? You want to know how many belongings I have, and how much they weigh, and whether any of them are alive and may make the
>>> sack bounce and jump around? Why oh why would you want to know that, just to tell me how big a cruddy rope needs to be?
>>>
>>> OK: I'll make a deal with you:
>>>
>>> _You_ tell _us_ enough about what you're doing (expected current draw, more about the parts that you're going to use, whether
>>> you're running any analog parts, etc.) Then maybe _we_ will have enough information to tell _you_ the answer that you need.
>>>
>>> And I'll go figure out that damn rope size myself.
>>
>> Perhaps you can hang yourself with it?
>
>Perhaps I could comment that there _are_ stupid questions?


There are no stupid questions, only stupid people.

John

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