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Old 11th March 2004, 07:47 PM   #101
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Quote:
2) Do I need to decouple digital ICs with Os-Con and ceramic capacitor in parallel?
Forget about using a ceramic cap in parallel when using OSCON. Try to place the OSCON as close to the pins as possible with short tracks.

I don't know what to answer on the first point, I use MRS 25 for everything.
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Old 11th March 2004, 07:50 PM   #102
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Originally posted by jean-paul


Forget about using a ceramic cap in parallel when using OSCON.

Why? Because it's not necessary, or because it will ring?

And will 0.1uF film caps be OK?
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Old 11th March 2004, 07:56 PM   #103
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Default Why?

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Why? Because it's not necessary, or because it will ring?
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Old 11th March 2004, 08:06 PM   #104
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As you refer to the document of Guido Tent I advise you to read it again for reference. The man knows his stuff and he also knows to explain it well. Way better than I can, I just try and test.

I like the comment of Peter Daniel on OSCON although I use them in digital circuits often. In analog I will never use them again as they are responsible for a metallic sound there as experienced by me several times. Decouple an opamp with them and you'll know OSCON has a break in period too but less than BG.
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Old 11th March 2004, 08:13 PM   #105
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Default Let me quote

Let me quote:

"When selecting an electrolytic, the series inductance must be taken into account, and properly compared with the total inductance of the supply loop the cap is in. That inductance of the (for a DIL28) package for example) is about 12nH. the ESL of the capacitor shall be relatively small compared to this value; it does not make sense to look for 2nH as the loop itself dominates!"

- i.e. the effect of a ceramic capacitor will be insignificant.
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Old 11th March 2004, 08:18 PM   #106
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Default Let me quote further...

"Modern electrolytics are far better RF performers. Their construction is such that the series inductance is very low (both films are terminated at the same side). They have very low impedance over up to 4 decades in frequency; Enough to say goodbye to the additional ceramic capacitor. It saves money and space as well and eliminates the risk of yet another resonance."

i.e. Os-Cons are good (enough) for the RF we are dealing with. Using a ceramic capacitor in parallel is asking for trouble.
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Old 11th March 2004, 08:22 PM   #107
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Could not have said it better BTW why ask if you know the answer ?
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Old 11th March 2004, 08:25 PM   #108
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Default I simply didn't believe it!

I had read Guido's words of knowledge, but I lacked confidence in applying what they were telling me. Indeed, Sanyo give PDF examples on their website where OsCons alone are used as decoupling devices.

So why do so many people believe in using ceramics and low impedance electrolytics in parallel? Are they simply wrong?

My asynchronous reclocker operates at 66Mhz. Are 0.1uF ceramic capacitors alone a better choice?
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Old 11th March 2004, 08:28 PM   #109
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If you don't believe an analog designer with a good reputation I doubt that you'll believe me ( I wouldn't ) as a DIYer so I won't comment anymore on the subject.
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Old 11th March 2004, 08:31 PM   #110
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I have used the OSCON because of Radial design and they have great ESR, also I can get them in one day. I normally use Sprague 550D low ESR tantalums which are great but cost 6 time as much as the OSCONs. I have not tried out the BG's, their are harder to get and they cost more.

Also, I have found if you running fast logic it still best to decouple with .1 or .01 on ever chip and the size depend on the ringing.

The last time I checked carbon film had a better tempco than carbon comps and I hate carbon comp's.
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