Volt-reg capacitors

Discussion in 'General Electronics Chat' started by kgstewar, Jun 4, 2014.

  1. kgstewar

    Thread Starter Member

    Apr 5, 2012
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    I have a project where I am using the Ti UA78M33 voltage regulator and I'm trying to figure out which capacitors to use. On the webpage that I linked, in the table labeled "Parametrics" under "Output Capacitor Type" it says "Cap Free non-ceramic". Any ideas what that means?

    In the datasheet there is no example circuit, but in footnote (1) on page 4 it talks about a 0.33uF cap on the input and a 0.1uF cap on the output. Other regulators I have used specify these same values.

    Am I correct that I should use non-ceramic caps (mylar? tantalum?) with this chip, based on the "non-ceramic" statement, or am I misreading that? On other regulators I have used ceramic for the output cap with no ill effects. The regulator is supplying voltage to a MSP430G2452 microcontroller.

    Thanks!

    Kevin
     
  2. ronv

    AAC Fanatic!

    Nov 12, 2008
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  3. kgstewar

    Thread Starter Member

    Apr 5, 2012
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    Thanks, very useful app note! So, it appears that some regulators have built-in circuitry that allows use of ceramic output caps, but based on the "non-ceramic" statement on the webpage, I'll assume that the UA78M33 is not one of them.

    I'm hoping to use SMD caps, and I assume tantalum would be a good choice for 0.33 and 0.1?

    Also, on the first page of the datasheet, one of the bulletted features that is touted for this regulator is:

    • No External Components
    Any idea what that means? The lack of an example circuit showing input and output caps at first led me to think that this statement meant that the regulator didn't require caps, but the footnote that mentions 0.33 and 0.1 caps seems to contradict that notion. This thing needs caps, right?


    Thanks!


    Kevin
     
  4. alfacliff

    Well-Known Member

    Dec 13, 2013
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    "no external componants" means the regulator needs no external componants. there is no circuitry on earth that "allows the use of ceramic caps". ceramic caps are normally used for the input and outpput caps because they have low internal inductance, and help bypass the input and outputs to prevent oscilation of the high gain internal amplifier. mylar caps usually have significant internal inductance.
     
  5. kgstewar

    Thread Starter Member

    Apr 5, 2012
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    Sorry, I'm not sure I follow. The tech note I just read states that ceramic caps are to be avoided, I believe.
     
  6. alfacliff

    Well-Known Member

    Dec 13, 2013
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    the no external componantrs is there because some earilier regulators required external resistors or diodes, or pass transistors, these do not require anything except the bypass caps which do not have anything to do with regulating the voltage, only to stop oscilations that might occur. the no ceramics makes no sense. unless it is talking about the packagng of the regulator.
     
  7. ronv

    AAC Fanatic!

    Nov 12, 2008
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    Better isn't always better. You have to read the app note.
     
  8. kgstewar

    Thread Starter Member

    Apr 5, 2012
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    App note seems to indicate that tantalum caps work well with this regulator, so that's what I'll go with. Thanks all!
     
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