1
\$\begingroup\$

I am searching an suitable input and output capacitor (for example MLCC) for following Low Dropout Regulator (LDO): Analog ADP151.

The datasheet says that the ESR of the caps should be between 0.001 and 0.2 Ω.

I know the ESR vs. Frequency graphs on the capacitor manufacturer pages, but at which frequency do I have to look to find a suitable capacitor?

\$\endgroup\$
  • 3
    \$\begingroup\$ Possible duplicate of Choosing capacitors for a linear voltage regulator \$\endgroup\$ – Artūras Jonkus Jan 12 '17 at 21:02
  • 1
    \$\begingroup\$ @ArtūrasJonkus - I don't see anything on that page that answers OP's question. They have similar titles yes, but they are very different questions if you bother to read them. \$\endgroup\$ – I. Wolfe Jan 12 '17 at 21:10
  • \$\begingroup\$ They are similar - person wants to choose capacitor. Only this time he thinks that ESR is kind of crucial. Anyway, if people don't think I'm right they won't flag it \$\endgroup\$ – Artūras Jonkus Jan 12 '17 at 21:20
  • \$\begingroup\$ When ESR is too low, the linear amp has too low phase margin with a capacitive load. When ESR is too high step loads causes excessive ripple due to insufficient gain to correct voltage error at max slew rate. <1mohm is possible but hard to achieve except in metal film.(plastic). but they are $$$ . So 1uF X7R or X5R as stated (in spec) is ideal \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jan 12 '17 at 22:35
4
\$\begingroup\$

Specification says, p.12

"A minimum of 1 µF capacitance with an ESR of 1 Ω or less is recommended to ensure the stability of the ADP151"

and

"Any good quality ceramic capacitor can be used with the ADP151, as long as it meets the minimum capacitance and maximum ESR requirements"

You will be very-very hard pressed to find a 1uF small ceramic cap with 1mOhm ESR, so you can safely ignore the contradictory statements from ADP151 specifications.

So the answer is: any ceramic cap will do the job, just as spec said.

\$\endgroup\$
  • \$\begingroup\$ beaten to the post, +1 for agility \$\endgroup\$ – Neil_UK Jan 12 '17 at 21:39
  • \$\begingroup\$ Any 1uF ceramic cap except Y5V and Z5U !! and not electrolytic unless ultra low ESR type and definitely not plastic. (too low ESR) \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jan 12 '17 at 22:28
  • \$\begingroup\$ And how about the max. rating of 0.2 Ω? Is this a problem with a ceramic X7R or X5R? Can I find those values in the datasheets of the cap or somewhere else? \$\endgroup\$ – I0BitMore Jan 14 '17 at 10:04
  • \$\begingroup\$ @I0BitMore: Yes, every reputable manufacturer (Murata, Kemet, TDK, Yageo, Panasonic, Vishay, etc.) do have ESR data charts for each capacitor over a range of frequencies. Example: psearch.en.murata.com/capacitor/product/… More data can be found here, mouser.com/ds/2/281/c02e-2905.pdf \$\endgroup\$ – Ale..chenski Jan 14 '17 at 17:04
0
\$\begingroup\$

ADP151 is an excellent regulator. Low noise, high PSRR...

I did transient response and impedance tests to check for output caps:

  • 1µF MLCC X7R will work fine, like datasheet says.
  • 10µF MLCC does offer improved transient response at minimal extra cost.
  • Going higher is only necessary for paranoid audiophiles.

This regulator isn't picky. FYI it has about 0.1 ohm output impedance and it begins to rise above 10kHz.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.