I would like to use the MP4430 for my 0.9V/3A rail with input range of 6V-19V and switch at 2.1MHz to reduce the inductor and capacitor sizes. Is this doable? If not, what are the limitations?
The buck power stage on-time at Vin = 19V, Vout = 0.9V, and Fsw = 2.1MHz is 22.6ns which is shorter than the MPQ4430 min on-time of 80ns (typical) so switching at 2.1MHz will not work. Reduce the switching frequency until the buck power stage on-time is longer than 80ns. 470kHz switching frequency is a good starting point as the buck on-time will be 100.8ns.