SMD capacitors for decoupling
Mar 15, 2006 at 1:22 PM Thread Starter Post #1 of 14

Alf

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I am looking for the best 0805 100nF capacitors for decoupling. Any recommendations would be much appreciated. Manufacturer? Series? Dielectric type? Something else?
 
Mar 15, 2006 at 4:20 PM Post #2 of 14

jcx

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you can get many different types in this size

in ceramic you should use X7R/BK7 - the lower "k" of the high K ceramics - the very high k types have huge V and T dependence and can be audibly piezoelectric (in switching supplies), go for the highest V rating you can find to reduce V related C nonlinearity

panasonic has 25 V film caps in this size - probably pen, a mylar relative

many data sheets still recommend large tantalum caps in addition, I would use polymer electrolyte Al in most of those apps today

a peculiarity of bypass/decoupling is that paralleling caps can produce resonant peaks in the impedance between the well separated srf impedance dips of each different size bypass cap - sometimes the better option is to use higher esr caps (~ 1 Ohm) to damp the peaks
 
Mar 15, 2006 at 5:09 PM Post #3 of 14

peranders

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I use X7R 100 nF 0805 in all my stuff.

The lastest one here: Current feedback with four super regulators.
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qrv08r0_overview.jpg
 
Mar 15, 2006 at 5:18 PM Post #5 of 14

rickcr42

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Quote:

I am looking for the best 0805 100nF capacitors for decoupling. Any recommendations would be much appreciated. Manufacturer? Series? Dielectric type? Something else?


AVX stacked film ceramics
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Mar 15, 2006 at 9:40 PM Post #9 of 14

Alf

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Quote:

Originally Posted by 00940
Speaking of smd decoupling caps, has anyone read that ? http://focus.ti.com/lit/an/sloa069/sloa069.pdf

On p.6 they advise to not put the caps flat on the pcb but to rotate them by 90°, in order to minimize resonances.




It is an interesting article. They recommend to use COG/NPO capacitors and ditch the rest.

Also the idea of vertical mounting is rather unusual. I have never seen this kind of mounting before.
 
Mar 16, 2006 at 4:34 AM Post #10 of 14

jcx

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the ti app note is about really high frequency (plate resonance graph is in GHz!) the highest frequencies head-fiyers are likely to encounter would be a tpa6120 cfa which might have a unity gain of 300 MHz if you select rf for some peaking

but while the principles are useful the specific recommendations aren't so practical for ~ 10 MHz gbw op amps running at gains of several as are common in audio apps

np0/c0g type ceramic simply aren't available in 100nF, you could solder up a stick like the smps guys do but it won't be 0805

BK7 / X7R should be fine in bypass appications and the larger C is useful when you don't require srf > 10s of MHz
 
Mar 16, 2006 at 5:34 AM Post #12 of 14

jcx

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Digi-Key Part Number 445-2672-1-ND
Manufacturer Part Number C2012C0G1E103J
Description CAP CER 10000PF 25V C0G 5% 0805

100nF = 100,000pF

I regularly spec this type of 10nF C0G cap, some Cap manufacturer's catalogues claim 22 & 33nF C0G have been made but they are not easily found in distribution

[edit: I thought I made a mistake once, but i was wrong - actually the previous link to AVX' catalog gives C0G sizes on pg 7,8]
 

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