UCC28600 soft start calculation

this equation calculates the minimum time required for soft start progamming so that the output capacitor bank is completely charged before the controller is fully running.  R_LOAD(ss) is the output load (Vout/Ioutmax) that the converter has to start into, delta Vout(step) is the allowable output voltage step change, and P_{OUT(max)limit} is the maximum output power that would trigger a power limit fault. 

This equation is derived from the capacitor charge equation of V(t) = Vo(1-e^-t/RC) allowing for 2 time constants (so 2t/RC is used).  This equation calculates the MINIMUM recommended capacitor that would result in the time required to allow the output capacitors to charge without the charge current surge triggering an overload response.  If the soft start time was less than the time it takes for the output capacitor bank to charge, the peak current on the primary side would be detected by the controller (because SS is over) and the increase in current due to the added capacitor charging current, would trigger a current limit response.