In LM3481 datasheet, I think equation 58 for RMS current through the link capacitor (Cs) in SEPIC configuration is wrong.
It does not give the same result as the equation suggested in TI article "Designing DC/DC converters based on
SEPIC topology" from Analog Application Journal Q4 2008.
During Ton, current through the capacitor is the current through L2.
During Toff, it is the current through L1.
RMS value I find using the full integral formula on that piecewise function is always very near Iin*sqrt((1-D)/D) as suggested in the article. Therefore, it looks right to me.
I am not quite sure where eq 58 comes from but it does not look right.
Frederic