As a part of a PCB, I want to use this AMS1117-3.3 voltage regulator with 22uF input and output capacitors as follows:

enter image description here

As for the exact part for the capacitors, I was planning to use this X7R capacitor for both input and output, but the voltage regulator's datasheet says:

The circuit design used in the AMS1117 series requires the use of an output capacitor as part of the device frequency compensation. The addition of 22µF solid tantalum on the output will ensure stability for all operating conditions.

Does that mean I cas use 22uF X7R as the input capacitor but I should use a 22uF tantalum type for the output?

I also saw a discussion on another question here.

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    \$\begingroup\$ are you really going to exclusively attach an LED, or will there be a dynamic load? note that the document you quote says "stability for all operating conditions", i.e., even under worst case oscillations of the load. An LED doesn't draw an oscillating current, AND you won't notice some ripple either, so your regulator has a far far easier job than if there's something attached that has a rapidly changing load current and requires good voltage regulation. \$\endgroup\$ Commented Jul 10 at 12:02
  • \$\begingroup\$ There will be an MCU and an SPI DAC chip and an I2C ref controlled by the MCU. But all will be powered by this regulator. LED is there just to indicate power ON. I didnt share the entire schematic. \$\endgroup\$
    – user1245
    Commented Jul 10 at 12:11
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    \$\begingroup\$ Most modern LDOs will be stable with ceramic capacitors. I'd choose a different LDO. Not following the manufacturer's recommendation is not a good habit to get into. The fact that a design may work - not fail - is a different standard of design quality than ensuring the design is robust and will always work. \$\endgroup\$
    – JkingNH
    Commented Jul 10 at 12:12
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    \$\begingroup\$ @RussellH I see thank you for this point. I guess its about inrush current when cap is high. Thanks! \$\endgroup\$
    – user1245
    Commented Jul 10 at 13:11
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    \$\begingroup\$ The AMS1117 requires a certain minimum ESR in the output for stability (I remember analysing it for a question several years ago - usually somewhere around 0.5 to a few ohms is required). When I see 'tantalum' for stability, I get suspicious. \$\endgroup\$ Commented Jul 10 at 13:17

1 Answer 1


The data sheet does not state what properties of the capacitor are important and in what range they should be.

Having said that, many older linear regulator data sheets recommend tantalum capacitors because these data sheets are from an era where tantalums were the most suitable capacitors, because they had lower ESR and worked over larger temperature range than standard electrolytics. These regulators are basically designed to be used with tantalums. Low ESR electrolytics did exist but were generally used for more expensive switch mode applications and ceramics such as X7R capacitors were not yet available in the capacities required or were expensive.

Often regulators need certain ESR range for stability of the feedback loop. Going outside the range means the regulator output will be unstable.

It is very likely that any ceramic cap you put there has way smaller ESR than the intended tantalum cap.

There are techniques that allow you to use a ceramic cap but it requires increasing the capacitor ESR by adding a small series resistor, or moving the capacitor further away from the regulator to add both ESR and ESL with the PCB wiring.

But as the ESR range is unknown, you don't know what would be a good resistor value for proper ESR range.

That does not stop from people using ceramic caps, but it may not be a good idea.

Changing one or two capacitors to tantalums just because your regulator would prefer one is also not a good idea for many reason. Tantalum caps are more expensive and less reliable, they may blow up simply because you exceeded the rated inrush current by hotplugging the USB supply to regulator input. It is also a conflict mineral.

It might be best to simply change the regulator to a more modern one which can work with simple ceramic caps, and their value will be less too.

Also note the USB interface has strict inrush energy limits and in addition to the resistive load, the capacitance cannot exceed 10uF, and likely 10uF on USB side and any capacitance on regulator output will exceed this limit. Better make it much below 10uF, the minimum you can or the regulator can tolerate.

Also cable plug/unplug events may cause large volage swings or ringing due to cable inductance and the extremely low ESR of the ceramic input cap. There could be one small 10 to 100 nF cap and the larger cap might still benefit from a damping resistor or simply use a series resistor between USB connector and regulator input with the bulk capacitor.


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