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The LM1117 voltage regulator datasheet recommends using tantalum capacitors on the input and output. What is the reason for this? What advantage does tantalum have over a ceramic capacitor?

A 10μF tantalum capacitor costs about 21 cents, while a 10μF ceramic capacitor costs about 3 cents. The ceramic capacitor is also a bit smaller physically. Plus, you don't have to worry about getting the polarity wrong on a ceramic capacitor. I believe there is also less concern about conflict minerals with ceramic capacitors.

What advantage does the tantalum capacitor offer, and why does the datasheet recommend tantalum for the input and output capacitors of the voltage regulator? What exactly would happen if a ceramic capacitor was used instead?

Note: To everyone who's claiming this is a duplicate of Why does the LM1117 data sheet specifically specify tantalum capacitors?, that question is about tantalum versus electrolytic capacitors, while my question is about tantalum versus ceramic capacitors. Related, but not the same.

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    \$\begingroup\$ Good question, but it has been asked before. You can find some info on this particular site too. There are very few reasons to use tantalum in any design and it's very good that you ask this question before blindly following the datasheet (like a lot of designers do). See electronics.stackexchange.com/questions/199479/… \$\endgroup\$ – LukeHappyValley Mar 29 at 9:12
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    \$\begingroup\$ You need to consider when the '1117 was introduced. Back then 10 uF ceramic capacitors were a) huge b) ureliable c) more expensive. \$\endgroup\$ – The Photon Mar 29 at 15:30
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  • \$\begingroup\$ Tantalum caps are definitely way more fun to work with than any other caps. No MLCC will catch fire all of a sudden just because you looked at it the wrong way. ;-) \$\endgroup\$ – TooTea Mar 30 at 12:16
  • \$\begingroup\$ @DmitryGrigoryev Sort of. The first link is about tantalum versus electrolytic capacitors, and does not mention ceramic, which is what my question was about. The second link is pretty close, although it is about a switching regulator rather than an LDO. \$\endgroup\$ – user31708 Mar 30 at 22:59
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The important part of the data sheet to read is this: -

enter image description here

So, if you choose a ceramic capacitor for the output, you might create instability in the LM1117 because a ceramic capacitor will likely have an ESR that is below 0.3 Ω.

This doesn't mean you can't use a ceramic capacitor - providing you are prepared to add a small value series resistor it will be fine. Generally, this "rule" applies on light loading scenarios. On medium to heavy loading, the load itself will "damp" the potential of the LM1117 to go unstable.

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The LM1117 is at least 15 years old, if not 20.

Back then large ceramic capacitors such as 10uF were not as common and cheap as they are now.

The chip output requires a capacitor with certain amount of minimum capacitance and certain range of ESR to work in stable operating conditions. Too low or high ESR and the regulator turns into an oscillator.

A tantalum capacitor fits this perfectly, and the chip might be even be designed to operate with a tantalum capacitor because they were common back then. Tantalums were the logical choise as they typically were smaller, had lower ESR and longer lifetime than typical electrolytic caps of the era.

Basically, large enough ceramics did not exist so they were more expensive. Electrolytics with their large ESR can be a problem. And using a modern ceramic cap can have too low ESR.

If you look at updated LM1117 datasheets from other manufacturers, such as OnSemi, they incude ceramic and aluminum electrolytic capacitors in the list of suitable caps, as long as they meet the capacitance and ESR requirements.

If you want to use modern ceramic caps with a regulator, don't use an old regulator that is not stable with ceramic caps.Instead, use a modern regulator that is made to work with ceramic caps.

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  • \$\begingroup\$ So... the long and the short of it is lower parts count. It's always about money. \$\endgroup\$ – Peter Wone Mar 31 at 0:25
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    \$\begingroup\$ @PeterWone No, not really about low part count as everything is a compromise you must weigh if it is worth it or not. Using tantalums allows for smaller product with wider temperature range that uses more expensive capacitors. Using electrolytics might be cheaper, but it makes the product larger which adds cost in PCB area of course, but due to ESR the temperature range is narrower. But that only applies if you need and LDO like 1117, it will be even cheaper if you don't need an LDO and use another regulator. \$\endgroup\$ – Justme Mar 31 at 4:42
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These day is quite rare to see recommended a tantalum over a ceramic. If it's an old regulator (like the 1117) it is possible that it needs some ESR to work, due to how the control loop is established: the load contributes to the pole/zero situation and the output filter is actually part of the loop compensation, it's not only there to supply transient.

In short, some regulators are simply not stable without something like 0.5 ohm of ESR, and the ceramic caps have usually no ESR to speak of. Tantalum have some (less than aluminium) so these would be stable. If this is the case you could run the regulator with a 0.47 ohm resistor in series with the output ceramic.

Another issue could be voltage derating of ceramics: as the DC bias rises on the capacitor the available capacity decreases up to 50%; it's a material issue, it depends on the dielectric (only class II have this problem, C0G and NP0 are stable with DC bias). This is simply solved using either a) a bigger capacitor (in Farads) or b) a bigger capacitor (in working voltage). With capacitors most of the time bigger is better, anyway.

There are also some other differences but I don't see how they could relate to a voltage regulator.

Also, check the datasheet date: it is also possible that at the time ceramics of the needed value weren't simply available

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  • \$\begingroup\$ With larger caps (>10uF) and in smaller packages, I've seen ceramic caps that can be reduced by 80% or more within their specified voltage ranges. ds.murata.co.jp/simsurfing/mlcc.html?lcid=en-us is an excellent detailed resource for ceramic caps and filters overall. \$\endgroup\$ – Cristobol Polychronopolis Mar 30 at 19:22
  • \$\begingroup\$ Thanks for the update, my last info was a derating of 50%. 80%? ouch \$\endgroup\$ – Lorenzo Marcantonio Mar 31 at 6:26
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Non electronic answer to compliment the others:-

It recommends Tantalum because it's old (FEBRUARY2000) and predates the ubiquity of multi layer ceramics. So then it was the go to material. Now it's widely classified as a conflict mineral, which is:-

In politically unstable areas, the minerals trade can be used to finance armed groups, fuel forced labour and other human rights abuses, and support corruption and money laundering.

These so-called 'conflict minerals' such as tin, tungsten, tantalum and gold, also referred to as 3TG, can be used in everyday products such as mobile phones and cars or in jewellery.

It is difficult for consumers to know if a product they have bought is funding violence, human rights abuses or other crimes overseas.

So now very politically incorrect. Reference from Europe. Similar (but more vague) legislation exists in the US.

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With the advent of compact inexpensive high-value (10uF and beyond, rated at 6.3, 10, 16V and so on) X5R and X7R (reasonable dielectrics) ceramic capacitors there seems to be much less reason to consider tantalum capacitors.

One of the differences is that tantalum caps have an ESR that is of the order of ohms. On some LDO regulators, that's an advantage, in that the LDO won't oscillate like a banshee. In such cases, I'd prefer to use a ceramic capacitor and a series resistor.

On some sensitive analog circuits, I think there may be an advantage to tantalums over ceramic caps in reduced microphonic (in ceramic caps, due to piezo-electric activity).

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  • \$\begingroup\$ You beat me to the comment about microphonics. A couple of years ago, we found increased noise on our signals when we closed the lid of the box. Normally you'd expect it the other way around with EMC. Turns out that some caps in the analogue side were microphonic, and they were "hearing" the fan blowing air over them. Not such an issue for digital, but it'll screw you on analogue. \$\endgroup\$ – Graham Mar 29 at 21:00
  • \$\begingroup\$ I omitted microphonics too because, well, it's not really relevant to the usual converter issues. But I have a couple of 10kHz charge pumps singing at power on \$\endgroup\$ – Lorenzo Marcantonio Mar 30 at 6:01
  • \$\begingroup\$ @LorenzoMarcantonio Yeh. My sister can hear the standby power LED on her HP laptop as it goes on and off. I can't, but we've tested it with her eyes shut. \$\endgroup\$ – Paul Uszak Apr 2 at 11:38
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Tantalum was used in the phone industry for many years.

It was the best choice in terms of capacity/volume ratio.

Tantalum ESR was and still is pretty high: 100 mOhm to 1 Ohm on the average.

There was a huge shortage of tantalum in 2000/2001 all over the world. Prices increased a lot.

Murata has been steadily working on improving the capacity/volume ratio of their ceramic capacitors and made huge steps ahead.

At the moment, the ESR of ceramic capacitors is much better than Tantalum.

To answer your question: I don't see any electrical advantage of tantalum capacitors.

I quit using them back in 2001.

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