Tantalum Capacitors - Doubt

Discussion in 'General Electronics Chat' started by mak., Apr 26, 2012.

  1. mak.

    Thread Starter New Member

    Apr 26, 2012
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    Hi All

    Tantalum capacitors are subject to Dead Short failure mechanism ie when a single capacitor fails, the entire drive will become dead. How to overcome this dead short failure ?
     
  2. #12

    Expert

    Nov 30, 2010
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    Don't apply more than the voltage the capacitor is rated for.

    For better answers, provide a drawing of the circuit the capacitor is used in.
     
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  3. MrChips

    Moderator

    Oct 2, 2009
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    Make sure you use good quality tantalum capacitors that are rated with a substantial voltage margin above the operating voltage.
     
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  4. mak.

    Thread Starter New Member

    Apr 26, 2012
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    Thanks for the instant reply. Great forum indeed.
    One more query.

    I read that tantalum capacitors are not tolerant of heavy charge and discharge currents. Can someone please quantify(average) the currents they are capable of handling
     
  5. #12

    Expert

    Nov 30, 2010
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    This comes down to heat. It can best be quantified by starting with the size of the capacitor in microfarads and physical size, and considering the frequency it will operate with. Again, the quality of the capacitor is a factor because equivalent series resistance is important.

    This datasheet can be very helpful.
     
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  6. mak.

    Thread Starter New Member

    Apr 26, 2012
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    Capacitor size : 33 microfarad, 3.2 X 1.6 mm (physical size)
    ESR : 3 ohm

    What could the charge and discharge current for this tantalum cap ?

    @ #12 .. Yeah, the datasheet was quite helpful..
     
    Last edited: Apr 26, 2012
  7. #12

    Expert

    Nov 30, 2010
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    On that datasheet I posted, this is a size A case with half the ESR of your capacitor.
    The datasheet shows .41 amps at 100 KHz so you might guess .205 amps at 100 KHz or find the datasheet for YOUR capacitor. Then you have to calculate for the frequency you are actually using. I'd expect a linear relationship for frequency.
     
  8. Wendy

    Moderator

    Mar 24, 2008
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    Tantalum caps have superior characteristics. Before they fail they can get noisy however. I was troubleshooting a fixture that was noisy when one of the caps went up like a match head. I had a can of cold spray in my hand, it made an impromptu fire extinguisher. Appropriate, since that was shorted it in the first place.
     
  9. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    Incorrect. Tantalums can still be blown up applying less than rated voltage because of inrush current. You have to limit the current to protect them. This is why the military does not allow solid tantulums unless such current limiting is provided. They did allow the use of high ESR wet slug Tantalums, which have poor electrical characteristics compared to solid tantalum.

    The surge current failure mechanism of solid Tants is not a quality issue, it's an inherent weakness of the type of cap. We actually had to pay the cap maker to surge test them on one military design we did to make sure they could handle the surge current in the design. They blew about 2/3 of the caps they tested to get enough for our need (small quantity) and then charged us for the blown ones as well..... turned out to be expensive.



    http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20080039306_2008037499.pdf

    Effect of Surge Current Testing on Reliability of Solid Tantalum Capacitors
    Alexander Teverovsky
    Perot Systems
    Code 562, NASA GSFC, Greenbelt, MD 2077 1
    A1exander.A.Teverovskv. 1 @gsfc.nasa.gov

    I. Introduction.
    Tantalum capacitors manufactured per military specifications (MIL-PRF-55365) are established reliability
    components and have less than 0.001% of failures per 1000 hours (the failure rate is less than 10 FIT) for grades D or
    S, thus positioning these parts among electronic components with the highest reliability characteristics. Still, failures
    of tantalum capacitors do happen and when it occurs it might have catastrophic consequences for the system. This is
    due to a short-circuit failure mode, which might be damaging to a power supply
    , and also to the capability of tantalum
    capacitors with manganese cathodes to self-ignite. During such a failure, a substantial amount of energy is released
    by exothermic reaction of the tantalum pellet with oxygen generated by the overheated manganese oxide cathode,
    resulting not only in destruction of the part, but also in damage of the board and surrounding components.

    A risk of using of an electronic component, and a tantalum capacitor in particular, can be defined as a product of the
    probability of failure and consequences (expressed for example as the cost of rework, retesting, redesign, project
    delays, etc.). In this regard, tantalum capacitors can be considered as low failure rate parts with a high risk of
    application. To reduce this risk, further development of a screening and qualification system with special attention to
    the possible deficiencies in the existing procedures is necessary.

    A specific feature of tantalum capacitors is so-called surge current or turn-on failures when the board is first powered
    up.
    The mechanism of surge current failures has not been understood completely yet, and different hypotheses were
    discussed in relevant literature. These include a sustained scintillation breakdown model [l-31; electrical oscillations
    in circuits with a relatively high inductance [4-61; local overheating of the cathode [5, 7, 81; mechanical damage to
    tantalum pentoxide dielectric caused by the impact of Mn02 crystals [I, 9, 101; or stress-induced-generation of
    electron traps caused by electromagnetic forces developed during current spikes [l I].
     
    Last edited: Apr 26, 2012
  10. #12

    Expert

    Nov 30, 2010
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    Don't apply more voltage than the capacitor is rated for.

    Glad you could clear that up for us.
     
  11. mak.

    Thread Starter New Member

    Apr 26, 2012
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    I have another query though not related to tantalum capacitors.

    What could be the access time for a 512 GB NAND flash operating at a temperature of 70 degree Celsius ?
     
  12. MrChips

    Moderator

    Oct 2, 2009
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    You should start a new thread.
     
  13. Wendy

    Moderator

    Mar 24, 2008
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    Agreed. But since this is also his thread I'll let it go.
     
  14. hgmjr

    Moderator

    Jan 28, 2005
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    This is just the type of information that a manufacturer typically puts in their datasheet for the part.

    hgmjr
     
  15. mak.

    Thread Starter New Member

    Apr 26, 2012
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    Is there any temperature Vs lifetime correlation for Tantalum Capacitors ? Can somebody please explain how reliable the Tantalum Capacitors are at higher temperatures (> 60 ⁰ C)

    Thanks
     
  16. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    Life does drop at higher temps. I don't know if there are reduction curves available, but 60C is pretty hot for a capacitor. This is unrelated to surge current failures which has nothing to do with temperature.
     
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  17. mak.

    Thread Starter New Member

    Apr 26, 2012
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    Can somebody help me get the Temperature Vs Lifetime curve for Tantalum Capacitor. That would help me a lot in my analysis.

    Thanks
     
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