Alt-BEAM Archive

Message #11964



To: beam@sgiblab.sgi.com
From: "Sathe Dilip" sathe_dilip@bah.com
Date: Thu, 16 Mar 2000 14:56:08 -0500
Subject: [alt-beam] Re: power filter caps question




> "Jeffrey B. Williams" wrote:

> 1) Does the cap, in parralell to the power pins of the IC filter all
> the variations (AC current) through it to the ground rail so that they
> do not influence the chip? (In other words, I'm clueless and would
> like an idea on why it works..)

More or less. The value of the capacitor decides what frequencies will
be sent to the ground. Smaller the capacitor, higher is the cut off
frequency beyond which it will be effective in sending the
variations/spikes/noise to ground. The type of the capacitor also
matters. An electrolytic capacitor will not do as good a job as a
ceramic in this situation

> 2. Can a put a single capacitor in parralell to a series of chips,
> cores, ....whatever to stabilize them, instead of a cap per chip.

No. Distributed is the word. One cap per chip (particularly the ones
that contribute to the spikes/noise and the ones that are susceptible to
the spikes/noise. The reason is, the cap has to be as close to the
source/target (of noise) as possible to be effective. Even the lead
length matters in severe cases. (PCB track/wire inductance and to a
lesser extent resistance helps noise in its dirty work)

> 3. What's a good size for these beasts. To be honest a single .22uf
> worked to stabilize my walker, but I still don't have that warm fuzzy
> feeling that tells me its not just waiting to go up in flames. I
> have the impression that they should be larger, but what is too large?

One 10kpF to 100kpF ceramic (monolithic chip ceramic - MLC is also fine)
capacitor per chip is generally good enough.

> Now that it's tamed, I don't know why its called a walker.... The
> thing runs and scampers pretty darn quick...

May be its practicing race walking? :-)

Dilip
--
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The early bird may get the worm, but the second mouse gets the cheese.
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11965 Thu, 16 Mar 2000 13:43:53 -0600 [alt-beam] FW: ....microcore question.... "BEAM Mailing List (E-mail)" "Scolman,Jim"




> Hi, the enclosed circuit is described as a master/slave bicore.......it
> seems more like a microcore, not like other master/slave bicores I have
> seen??......I'm new soooooo in this diagram where does the power go? If
> I want to leave off the sensor for now, are the two sensor pins connected?
> What do you think about this circuit and servo motors and a solar
> cell?......thanks....JWS.
> <>
> Jim Scolman
> AMS Services, Inc.
> Bothell, WA
> 425-402-1000 x353
> 206-910-6095
> scolmaji@amsworld.com
> Network Administrator
>



Attachment: WalkerCircuit.jpg

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