LTSpice SEPIC design low freq ringing
After much tweaking of the C4, L1 &amp; L2 values and the slope compensation components, I managed to get waveforms that have much less low frequency component.
I have settled on slightly more L (27uH), slightly less C (2u2) and much the same C8 &amp; R6.
It would be nice if LT offered a design solution that helped with these calcs!



Note these waveforms are with a sine output load at 400Hz not the step shown in the original post. Green is OP voltage, Blue inductor current and red load current.