Switch voltage drop is often used in turn ratio calculations, however it is rarely specified in datasheets for converter ICs with built-in FETs. The closest I found is "Rds at Isw". Should I multiply these and use everywhere? Or should I multiply Rds by estimated Iavg or Ipeak? When Vin is low this produces rather huge difference, like 1:5 vs 1:10.
I think I found an answer on powerelectronics site:
MOSFET conduction loss PCONDmosfet = Imosfeton(avg)^2 x RDSon x D
if PCONDmosfet = Vsw * Imosfeton then Vsw = Iavg x Rds x D
Looks pretty much as I expected, except for that D multiplier.