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I'm looking for a capacitor to use as the output capacitor with the LDO regulator SP6205EM5-L-3-3. It says it requires a 2.2 µF capacitor, with an ESR less than 0.5 ohm.

I've found the TCJA106M010R0300 type of tantalum capactior would suffice.

However, these are quite expensive, almost half the cost of the regulator... I wondered if ceramics of type C3216Y5V1H225Z/0.85 (in the specification it says ceramics are allowed) would have the low ESR required (they say 'Low ESR', but it does not have a value specified).

What does low ESR mean at the frequencies involved with this regulator?

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The part's datasheet says "Unconditionally Stable with 2.2μF Ceramic", so I think you're good.

(Ceramics have lower ESR than tantalum or aluminum electrolytics.)

Notice the note about increasing the capacitance if you decouple the BYP pin.

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  • \$\begingroup\$ Hi Mark, So the ceramics I've now linked too (needed more rep) will have lower ESR than the 300mOhm tantalums ones? Thats great - I just didnt understand what 'Low ESR' means... yep I've included the 10nF bypass cap - how high should I go with the ceramic in this case? Thank you! \$\endgroup\$ – James Apr 25 '11 at 8:21
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The ESR of a ceramic capacitor is so low it is fairly common to disregard it altogether for practical purposes in DC regulators. The main reason I find to use tantalum instead of ceramics as output caps is if you have problems with piezoelectric ringing in the ceramic caps.

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  • \$\begingroup\$ Hmm... how often is the ringing you mention a real problem? Will it add noise or cause the whole thing to go unstable? (LDO) If a datasheet has a example circuit with tantalum, should I take that as a requirement? Many times I think they're just arbitrarily showing you what someone's done before with the chip. \$\endgroup\$ – darron Apr 26 '11 at 19:30
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    \$\begingroup\$ Ringing is fairly common for ceramic output caps. It can help to change to a higher spec part (higher voltage or better dielectric) or a different package size. Tantalum is an easy fix as they are not prone to microphonics. \$\endgroup\$ – morten Apr 27 '11 at 6:53
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    \$\begingroup\$ The ringing produces a small voltage noise, but it won't cause instability in a DC converter. I would not take tantalum output caps as a strict requirement. \$\endgroup\$ – morten Apr 27 '11 at 7:02
  • \$\begingroup\$ On the topic of replacing (or not) tantalum with ceramics, the ESR of ceramics can in fact be so low as to require a series resistor in some applications, as explained for instance in TI's app note SLVA214A "Ceramic Capacitors Replace Tantalum Capacitors in LDOs" and also at element14.com/community/community/news/blog/2012/04/30/…. \$\endgroup\$ – Fizz Dec 11 '14 at 5:19
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The linked page does specify ESR, 300 milliOhm

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    \$\begingroup\$ For the ceramic? Where? All I see is < 0.05 DF. \$\endgroup\$ – markrages Apr 25 '11 at 4:11
  • \$\begingroup\$ [link]search.digikey.com/scripts/DkSearch/… These are the ceramics, it wouldnt let me link with low rep. \$\endgroup\$ – James Apr 25 '11 at 8:22
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    \$\begingroup\$ @James: The only mention of "300" on that page is in the price. Seriously, where? :) \$\endgroup\$ – Roman Starkov Apr 25 '11 at 10:34

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