The decoupling capacitor…is it really necessary?

RE: The decoupling capacitor…is it really necessary?

Art Kay — Thu, 06 Sep 2018 22:05:35 GMT

Venkatesh P17,

I am usually very conservative when it comes to choosing the voltage rating on capacitors. I choose the rating to be at lease 2x the maximum expected voltage on the capacitor. So for example, if I am using a 15V supply I will make sure the capacitor is rated for 30V or more. Generally, it is easy to find a 0.1uF X7R capacitor in a small package (e.g. 0603, or 0508) that will meet my requirements. The voltage rating has three main concerns. 1) exceeding it can damage the capacitor, 2) approaching the rating can de-rate the capacitance value, 3) the voltage rating may be de-rated over temperature. In cases where you cannot use the conservative approach you need to get detailed specifications on the capacitor and understand if the rating will work for your application over termperature.

RE: The decoupling capacitor…is it really necessary?

Venkatesh P17 — Mon, 03 Sep 2018 07:54:42 GMT

Thank you for very useful data., How to choose voltage rating of the capacitor? Because I heard different answers from different people.

RE: The decoupling capacitor…is it really necessary?

Art Kay — Mon, 17 Mar 2014 22:23:45 GMT

Natallia,

I wrote a text book on noise "Operational Amplifier Noise, by Art Kay". Also, below is a link to a short video on the subject. I will probably do some further blogs on this subject.

Art

www.youtube.com/watch

RE: The decoupling capacitor…is it really necessary?

Natallia Holubeva1 — Mon, 17 Mar 2014 17:03:27 GMT

Dear Art,

Thank you for the post. I was wondering if you have other useful posts regarding low noise design?

Tahnk you,

Natallia

RE: The decoupling capacitor…is it really necessary?

Seong-Yeol Choi — Mon, 02 Sep 2013 00:38:22 GMT

Dear Art,

This experiment data is very useful for junior engineer. Thank you very much.

RE: The decoupling capacitor…is it really necessary?

Jeff Louis — Mon, 02 Sep 2013 00:07:13 GMT

Another perspective is to treat the opamp as being supplied mostly from the decoupling capacitor; that the PCB power traces (due to their length) are only for d.c. supply and are sized just for low resistive drop. Depends on the load current and size and number of capacitors you can place next to the opamp though, but for driving ADC inputs the load is often very light at d.c.. Taking it further, you can even insert a resistor or inductor in the power supply trace as a cheap form of isolation from the system supply if you can't afford a local regulator.

RE: The decoupling capacitor…is it really necessary?

Iljoski Emilijan — Sun, 01 Sep 2013 13:15:50 GMT

Dear Art,

In this occasion, I will just say that this subject is much more complex than you presented it here!