Buck converter calculations

Hey All,
couple of questions regarding the ADP1850 buck converter.
Under ‘Setting the current sense gain’ calculating V_CSMAX requires the Rdson_MIN and MAX resistance. Is this RDSon value from the datasheet of the mosfet or something else. The max is not defined so i presume it is the same like MIN.Then there V_COMMAX where the ton is required. How can i calculate this ?

The duty cycle is Vout/Vin = 8.1/12 = .675 which is 67.5%. So the high side mosfet is ON 67.5% of the time.