From the datasheet I read, ***The feedback input circuit at the FEEDBACK pin consists of a low impedance source follower output set at 1.65 V.***

My guess is  this FB is used to provide a gain ratio to multiply Vref to the output , (Rf+Rs)/Rs * Vref = (13k+2.05k)/2.05k * 1.65 = 12.375V  But the Si diode drop must be added.  But the App Note ought to give better info.