Why recommend tantalum over ceramic capacitor for voltage regulator? [duplicate]

Question

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.

Answer 1

The important part of the data sheet to read is this: -

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.

Answer 2

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.

Answer 3

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

Answer 4

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.

Answer 5

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).

Answer 6

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.