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More filter cap nonsense...

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By roach
-  Fri Sep 22, 2006 7:38 am #19399
Philba wrote:I use a 100n bypass cap for each IC I use. I never combine them. It's cheap insurance against really hard to track down problems.
Right. My specific concern here is that the reference design for the VS10XX family of MP3 decoders (available here) states that there should be a seperate 100n bypass cap on each supply pin. Since there are 10 supply pins (4 x CVDD, 3 x IOVDD, 3 x AVDD), that ends up taking a lot of space on the PCB. I had noticed that Sparfun's (Olimex's?) design for the VS1002 breakouts and dev boards that they had combined the caps into a single 10u cap for each signal, and wondered if this was a common practice. Since there is an additional signal (CVDD) on the vs1033, I was hoping to use this "capacitor merging" technique in my vs1033 design. I don't want to remove the bypass caps altogether, just want them to take less space on the board...

So far, I still don't know whether that's possible or not...

By Philba
-  Fri Sep 22, 2006 8:53 am #19402
ah, sorry for not understanding. I don't get why they are using a 10 uF in place of 10 .1 uF caps. If you are doing surface mount, it's not so bad to put the caps there. I don't think I would join the 3 voltages together (IOVDD, CVDD and AVDD). Maybe join each with a single cap - i.e. all IOVdd pins share a 330n. This presumes that the 3 Vdds are in fact handled seperately in the chip.
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By roach
-  Fri Sep 22, 2006 9:05 am #19404
Philba wrote:I don't think I would join the 3 voltages together (IOVDD, CVDD and AVDD). Maybe join each with a single cap - i.e. all IOVdd pins share a 330n.
This is exactly what I'm trying to do, but want to make sure I don't smoke the chip.

By reklipz
-  Fri Sep 22, 2006 10:46 am #19406
The vs1002 datasheet shows only one set of caps per supply.
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By roach
-  Fri Sep 22, 2006 11:09 am #19407
reklipz wrote:The vs1002 datasheet shows only one set of caps per supply.
Hmm. So it does... I was focussing on the Application note (linked above) that supposedly describes a typical application across a bunch of VS10XX products, including the 1002 and 1033. The datasheet for the 1033 has almost the exact same schematic as in the 1002, but with seperate caps for each supply pin (10 in total).

I guess that answers that question...

By Philba
-  Fri Sep 22, 2006 12:44 pm #19411
you wouldn't smoke the chip, but you would get maddening glitches...
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