Decoupling caps-Alternatives to tantalum capacitors in digital circuits? - diyAudio
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Old 4th February 2005, 12:18 PM   #1
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Default Decoupling caps-Alternatives to tantalum capacitors in digital circuits?

All,

While tantalums appear to do a great job of decoupling power supplies in digital circuits, we have all heard of the disasters associated with cpas that appear to have shorted out etc. I have an old but great DAC and want to replace the tants decoupling the DAC.

Anyone with any ideas on caps that could be used to replace the tants? No black-gates please-they're outside the fiscal abilities of this diyer!
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Old 4th February 2005, 12:45 PM   #2
Werner is offline Werner  Europe
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Rubycon ZA?
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Old 4th February 2005, 01:15 PM   #3
hifi is offline hifi  Sweden
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Oscon SA/SC/SH
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Old 4th February 2005, 01:31 PM   #4
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Default Many options

The multi layer ceramics work great, but they are small value and expensive. I like using the Siemens style naked stacked film and foil caps, the largest are 2.2 ufd.
The Oscon listed above are perfect. I picked up some 6.3 v, 390 ufd SP series from www.capacitorsplus.com. These are very small and extremely low impedance. They ared better than the BG for this application and are much cheaper.

George
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Old 4th February 2005, 03:14 PM   #5
gmarsh is offline gmarsh  Canada
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What's wrong with tantalums? They're very reliable, assuming you design a circuit correctly and pick the correct part.

Tantalums do *not* like excessive voltage, negative voltage, or excessive current beyond their ratings. And when they fail, often times they'll short the rail (discharging every other capacitor on the rail into themselves) blow their case open and let air in - then the tantalum element of the capacitor will (literally) burn.

If you have only a few 6.3V tantalums decoupling a lot of high speed 5V logic, it's very possible to see fires happen, and I've seen this first-hand. But for someting as simple as a DAC, there's really nothing to worry about.

I'd leave them in there if the DAC works just fine. But if you insist on replacing them...

My "favorite decoupling capacitors of all time" are the X5R, 47/100uF, 6.3V, 1210 multilayer ceramics made by Panasonic, AVX, Murata, etc... they have absolutely incredible ESL and ESR numbers, and plenty of capacitance. These have exploded in popularity with new multi-MHz/multi-phase switching power designs, and they're becoming very cheap.

And for large uF, low-volts decoupling, you can't beat OS-CON, AO-CAP, KO-CAP or any other organic semiconductor/specialty polymer capacitor. Almost every capacitor company makes these now.
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Old 4th February 2005, 04:29 PM   #6
jcx is offline jcx  United States
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Default tantalum mining is bad for environment

I don't design in tantalum any more:

http://www.diyaudio.com/forums/showt...ht=#post555995

however i wouldn't bother replacing ps bypass tants, unlike al electros they don't dry out so life should be near infinite

the new high valued ceramics should be checked for piezo response, i have heard them scream in sw ps
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Old 4th February 2005, 04:43 PM   #7
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Running a 6.3 V tantalum at 5 V is asking for problems. I would not use anything less than 15 V in that application. You can not chose voltage rating in the same manner as you do a conventional electrolytic.

Jocko
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Old 4th February 2005, 06:56 PM   #8
gmarsh is offline gmarsh  Canada
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Quote:
Originally posted by Jocko Homo
Running a 6.3 V tantalum at 5 V is asking for problems. I would not use anything less than 15 V in that application. You can not chose voltage rating in the same manner as you do a conventional electrolytic.

Jocko
On the contrary, many commodity half/quarter-brick power supplies use 6.3 volt tantalums as the output filter capacitors on 5 volt outputs. They're pushed close to their current ratings and voltage ratings at high temperatures. And they work great...

And the reason they work great is because power conversion companies don't just throw parts at boards, they analyze the hell out of everything they make to ensure sure it will work beyond spec. They might pick 10 different capacitors, find a good one, then redesign the rest of a power supply to suit that capacitor. And then they'll analyze/test everything all over again.

Reliability data for tantalum capacitors (as well as electrolytic, ceramic and so forth) has been extremely well studied.

And you can't just "up the voltage ratings" and expect instant safety - a 15V tantalum typically has higher ESR than a similar 6.3V tantalum from the same part series and manufacturer. Which means that in a high current 5V application, the 6.3V part might work just fine but the 15V part might get hotter from I2R loss and fail prematurely...

The only bad thing about tantalums which I've read about, is that people that work in tantalum mines hunt endangered monkeys near the mines for their meat.
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Old 4th February 2005, 07:17 PM   #9
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BG nx-hiq sounds best - why not just use them........?
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Old 4th February 2005, 08:17 PM   #10
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Quote:
Originally posted by gmarsh
The only bad thing about tantalums which I've read about, is that people that work in tantalum mines hunt endangered monkeys near the mines for their meat. [/B]
FYI (not trying to convince) -- http://www.heise.de/tp/r4/artikel/12/12860/1.html

Regards
theduke
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