The reason I need 2 stages is because I want to do parallel FET dimming for groups of leds. with all leds connected in series.
I have a 4th winding to generate 5V for a MCU which drives the FETs for dimming.
If I used the TPS92310 (single-stage) and only needed 1 led on (Vls low), the Vlaux, as well as the 4th winding voltage, would be too small (linked with the Ls voltage) and the whole system would shutdown (I guess).
That being said, I don't understand how the UCC28810 would work, provided that is also a constant current controller. And I would like to avoid opto-couplers and use Primary-Side Regulation.