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Old 19th September 2005, 11:33 AM   #1
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Default High capacitance from small packages for analog decoupling?

I am currently building a project where I have trouble finding room for all the capacitors I require. I am most worried about the analog section where the datasheet suggests I need 10-50uF in places. The vendor's evaluation module uses high quality through-hole Electrolytics, but due to the geometry of my layout I need to use SMD.

High capacitance from small packages is what I need. I have found film devices which offer up to 1uF in SMD1210. However stacking 10 such units is not desirable so my current plan is to stack say:

1. Silver Mica SMD1210 device
2. two film SMD1210 devices on top
3. one AVC TacMicrochip device on top of that again for the bulk capacitance. http://www.avxcorp.com/docs/catalogs/taclp.pdf

The AVX device seems to offer very high capacitance, low volume, low leakage and reasonable impedances and 15uF in 10V (I operate at 5V analog). What I am not so sure about is the dielectric loss.

In the past, Tantalum capacitors seemed to be shunned by users due to their failure modes (short) and often catastrophic failures. What I have yet to find is a consideration of how well these units perform in audio. These units seem ideal for my needs - your comments on this matter would be greatly appreciated.

Petter
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Old 20th September 2005, 03:09 PM   #2
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From elsewhere someone recommended Panasonic SP (Specialty Polymer). These seem like fine units but are rather large at SMD 7343 (7.3mm by 4.3mm). I have found film devices I could use beneath such units but with limited capacitance of a few uF.

I would still be pleased for other suggestions.
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Old 21st September 2005, 11:08 AM   #3
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Try the murata GRM32ER60J107ME20

Ceramic, 100uF, 6.3V, X5R, 1210
ESR=1mOhm, ESL=2nH, fres=400Khz

TDK makes a similar devise, but I can not remember the product number.

I hope this helps you

\Jens
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Old 21st September 2005, 12:50 PM   #4
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More info here:

http://ur-group.co.uk/artesyn/cd/pdf...n_pth12050.pdf

\Jens
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Old 21st September 2005, 01:35 PM   #5
Loial is offline Loial  Sweden
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Why not use SMD electrolytics?
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Old 23rd September 2005, 02:25 PM   #6
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I am using ceramics on the digital side, but am worried about them for the analog side, particularly the low capacitance units.

SMD electrolytics work, but I was looking for something even smaller + they seem harder to handsolder.

Petter
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Old 23rd September 2005, 05:38 PM   #7
Loial is offline Loial  Sweden
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I agree small SMD electrolytics are a real pain in the *** to solder ( and desolder is eaven more tricky... )

I just remembered that I've got a bunch of 6,8 uF 50V ceramic caps ( actually two caps in one ), measuring approx. 5*7*5 mm.
Really easy to solder, I attached an image of it.
Petter - I could send you a few if you'd like, for some coffe-money 5-10 pcs? Where in scandinavia do you live?

By the way... with "small packages" - how small do you mean?
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Old 25th September 2005, 08:43 AM   #8
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How small:

SMD1206 or 1210 would be really good for me but if really large film units can be found, larger is OK. The only problem is that the 1210 units I plan to use are 1uF and the largest "normal" SMD sticks I have seen (in film) have been only a couple of uF thus not really worth the effort as stacking 5 of the small ones is probably just as good as using the big ones + don't cause the same layout issues give that things are getting so tight.

Petter
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