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MLCC experience/suggestions?

Discussion in 'Electronic Design' started by starfire, Jun 23, 2007.

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  1. starfire

    starfire Guest

    Does anyone have any experiences (good or bad) with using MLCC-type caps for
    input power / voltage regulator applications? I'm using 22uF Tantalums
    right now and have reduced (but not eliminated) some heavy switching
    transients. The MLCC looks good in terms of no polarization and reduced
    package size for the capacitance rating.

    Is there a source for these caps (in 47uF or 100uF flavors) at prices lower
    than DigiKey? DigiKey wants $23.48 for ten 100uF, 6.3V caps. I realize
    this is a relatively new technology but has anyone run across a more
    inexpensive source?

    Thanks.

    Dave
     
  2. Eeyore

    Eeyore Guest

    There's nothing new about MLCCs !

    What do you want 100uF for ?

    Graham
     
  3. Nico Coesel

    Nico Coesel Guest

    Perhaps smaller sizes are cheaper in the end. I've been using MLCC for
    several years now. They work fine and I like the fact MLCC is not
    prone to burn a hole in the PCB. Another positive thing about MLCC is
    that they are better for the environment. Mining tantalum does a lot
    of damage to the plants and animals.
     
  4. Eeyore

    Eeyore Guest

    Does it ?

    Can you explain how it does that ?

    Graham
     
  5. John Larkin

    John Larkin Guest

    Ceramics are great, and values like 10 or 22 uF are affordable. But a
    lot of regulators will oscillate into a big ceramic load, including
    most LDOs and LM337.

    John
     
  6. Nico Coesel

    Nico Coesel Guest

    I can't understand why I even bother to post this *, but here it goes:
    First hit with Google:

    http://www.cellular-news.com/coltan/

    * I must be in a really good mood since we're about to have lasanga
    for dinner.
     
  7. Eeyore

    Eeyore Guest

    Poor gorillas.

    I've never specced a tantalum cap in my life. I've always been slightly puzzled
    why they're so popular in cellphones.

    Graham
     
  8. starfire

    starfire Guest

    Now that's EXACTLY the kind of information I was looking for! Thank you!

    So often people get sidetracked by picking on the exact verbiage used to
    format the questions that they overlook the context of the question...

    I had a problem with switching transients on an LDO which a larger input
    capacitor seemed to reduce. I had been using a 1uF ceramic on the
    input-side and a 1uF ceramic on the output-side of a TC1108 LDO regulator.
    Max current draw at 3.3VDC was about 100mA. Per great suggestions form this
    group, I inserted a larger 22uF Tantalum on the input-side and the problem
    was significantly reduced. While the switching transient was reduced to the
    point of not causing a problem with board operation, it was still there, but
    greatly reduced in amplitude. The voltage dip only dropped to about 2.5VDC
    from the nominal 3.6VDC input and there was virtually no overshoot when the
    transient ended about 2usec later. I had thought to increase the size of
    the input cap to 47uF, 68uF, or even 100uF. I also just found out about
    MLCC caps (I'm sorry... I must have been living a sheltered life:) ) and
    saw the reduced size for the footprint as well as the non-polarized
    components.

    Since these components are relatively high cost ($23.48 for 10 parts from
    DigiKey), would I be wasting time and money to try something like the 100uF
    1206 device for the input-side LDO filtering?

    Thanks.

    Dave
     
  9. Eeyore

    Eeyore Guest

    Why a tantalum ?

    Graham
     
  10. Winfield

    Winfield Guest

    You can solve that problem by adding a little series resistance.
    DigiKey has a good stock of multiple sizes of SMD resistors with
    resistances of 5, 10, 20, or 50 milli-ohms, or whatever your choice.
     
  11. starfire

    starfire Guest

    small size. only needed 6.3v working volts but needed small footprint.

    Dave
     
  12. starfire

    starfire Guest

    Is this to compensate for the lower ESR of the MLCC devices?

    Dave
     
  13. Matt

    Matt Guest

    This paper may be of interest:

    http://dkc1.digikey.com/us/en/mkt/NewT043/Panasonic/MLCC_whitepaper_081004.pdf
    The datasheets for National LM3670 and LM3671 (LDO efficient DC-DC
    regulators) have reference designs that call for MLCCs, and they provide
    part numbers.
     
  14. starfire

    starfire Guest

  15. John Larkin

    John Larkin Guest

    I want a cap to have a low AC impedance, so it seems silly to add
    another component just to make esr worse. It's better to use
    regulators that are stable with low-z loads.

    John
     
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