low esr capacitors

Discussion in 'General Electronics Chat' started by johnkaz77, Sep 22, 2010.

  1. johnkaz77

    Thread Starter Active Member

    Sep 20, 2010
    Hi,i am using TPS76918 voltage regulator and i noticed that it requires low esr capacitors at the output.What does it mean and what kind of capacitors i have to use?With what specifications?
  2. marshallf3

    Well-Known Member

    Jul 26, 2010
    There's no real "standard" regarding what can be called low ESR, all you can do is believe what they claim.

    They're probably trying to keep you away from just putting a 0.1 uF or something on the output.

    I notice they recommend a 4.7 uF with a maximum ESR or 0.2 ohms. Those shouldn't be hard to find, or you can just use a slightly larger cap to meet the ESR requirements.
    Last edited: Sep 22, 2010
  3. retched

    AAC Fanatic!

    Dec 5, 2009
    Just about anything you buy new. ;)

    Tantalum caps and even ceramic caps are low-esr.

    Electrolytic caps have the highest esr that I know of, and you can find special marked "LOW-ESR" electrolytic caps.

    If you are using the caps for decoupling and/or to prevent oscillation, ceramic will be just fine.
  4. tom66

    Senior Member

    May 9, 2009
    Sometimes low ESR capacitors are called low impedence.

    If you are using ceramic capacitors, the ESR for ceramic caps is usually so small it can be neglected. If you are using electrolytic capacitors, it is important.

    The line is blurred between low ESR and normal caps - there is no definite point at which a capacitor is low ESR or not.

    A low ESR capacitor basically means the capacitor has low equivalent series resistance. Think of a parasitic resistor in series with the cap. If you try and draw current from the capacitor, this resistor produces heat. It also increases ripple voltage.
  5. beenthere

    Retired Moderator

    Apr 20, 2004
  6. marshallf3

    Well-Known Member

    Jul 26, 2010
    Yea, you can enter the ESR as a filter in Mouser's drill down selection database too.

    Remember that you're working with low voltages, the selection of leaded electrolytics in that area have dwindled but you can find about anything in surface mount.

    They list several options in the datasheet as acceptable:
  7. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    You can also put a ceramic (say 0.1 uF) in parallel with an electrolytic of 4.7 uF to have a similar effect as a low esr capacitor of 4.7 uF. A lot of datasheets will show multiple capacitors in parallel instead of a single larger one.

  8. The Electrician

    AAC Fanatic!

    Oct 9, 2007
    They recommend a minimum ESR of 0.2 ohms, and a maximum of 10 ohms.

    This is typical of low dropout regulators--the ESR can't be too low.
  9. gootee

    Senior Member

    Apr 24, 2007
    Exactly right. Use a cheapo electrolytic.
  10. marshallf3

    Well-Known Member

    Jul 26, 2010
    Gotcha, need some sort of impedance o the circuit.
  11. The Electrician

    AAC Fanatic!

    Oct 9, 2007