WEBENCH® Tools/LM5122: how to calculate power dissipation of capacitances

You need to calculate the ripple currents, and the RMS of the ripples current multiply the ESR of the capacitor gives you the estimated power dissipation.

For the input current rms current, it is given by SQRT(1/3) x I(pk-pk) x 0.5, where I(pk-pk) is the inductor peak to peak ripple current.

Four output current rms current, it is approximate Iout / SQRT(1-D)

Hope this clarifies.

Here are the actual equations based on Youhao's description.

Thank you Gerold. Sorry my mistake for the output capacitor rms current. What I showed previously was the rms current through the rectifier. The rms current flowing into the output capacitor is approximately given by:

Iout x SQRT[ D /(1-D)]

Namely the capacitor ripple current is the rectifier current minus the load current. Sorry for the confusion.