Capacitor selection with current rating for switching regulator

Question

The example design parameters in the TPS54332 datasheet are as follows:

In the input capacitor selection section, the values confused me.

Selected capacitors parameters are 10uF, ceramic X5R, 25V, 3mΩ ESR, 3A current rating.

But in ceremic capacitors these parameters are not specified and I am not sure if they can meet these values.

Although these values are specified in electrolytic capacitors, they do not meet these values. I can only see these values on polymer capacitors but I don't want to use them.

I'm having the same confusion for the output capacitor. Is there something I got wrong? Would it be a critical mistake to make a design by ignoring the capacitor's ESR and ripple current?

Answer 1

The info is a bit hard to find.

For Murata, you can use their website (click on ceramic capacitors).

Then, picking a capacitor, you can plot "Temp rise" (orange button) which will tell you how much hotter above ambient the capacitor will be depending on ripple current.

You can also plot its ESR by clicking "Frequency characteristic" tab, then "R" button.

The "Product details" page will also give useful curves. Here's an example. It's quite convenient that your 1MHz DC-DC frequency corresponds to the minimum impedance point of these 10µF caps, which is also their ESR.

Would it be a critical mistake to make a design by ignoring the capacitor's ESR and ripple current?

Yes, always. If it's an electrolytic, it can pop from overheating, and if it's a tantalum, it can roast your board. But ceramics tend to have ridiculously good ESR and ripple current rating for the size, so in this case it's pretty easy.

In addition, the capacitor will have several vias to the ground plane, and most likely either a power plane or copper pour attached to it. Both act as heat sinks, making a tiny cap able to dissipate a surprising amount of power. At this current, make sure you don't use tiny traces, not just for heat, but you need the low impedance of a large copper area.

If you're worried, put several in parallel.