Electronic – Choosing a large, reliable input capacitor for switching regulator

capacitorswitching-regulator

A project I am designing has to be reliable for many years. I have a switching power supply using a LM2596S-5.0/TR

I am having trouble deciding on the capacitors. I have placed a tantalum 10v 220 uF on the output but on the input I am having trouble.

The datasheet says:

A low ESR aluminum or tantalum bypass capacitor is needed between the input pin and ground pin.

The example application lists a 660uF.

Looking on LCSC, I can only find a couple of SMD capacitors at 50V, 660 uF and they don't mention their ESR.
It doesn't help that the datasheets are in Chinese.

I can't seem to find tantalums of this size and voltage either.

Can anyone recommend the types I could use here? Favouring reliability if possible.

Best Answer

For a buck converter like this, it is very important to have a low ESR ceramic capacitor directly at the input of the converter. Otherwise you will have EMI problems.

So it is a common practice to put a small (10nF) ceramic cap directly at the input. For the bulk capacitance, you can then use the proposed 680uF (low cost) aluminium capacitor. (I would not recommend a tantalum capacitor for this).