Even the 20-pin TPS74801 QFN variant will probably overheat with the load proposed.
E.g.
Vin=5V, Vout=1.1V, Iout=1A (assuming "average") -> (5-1.1)*1 = 3.9W
3.9W * 35.6C/W + 30C ambient = 168C
Absolute max is 150C, probably want to keep it under 100C if you want to operate for a long period of time.
It would probably work if you could get a TO220 LDO regulator like a LT3080 and put it on a small heatsink.
In that case I think a LDO is much simpler and cheaper. Just find one that can down to 0.8V and re-cycle the 1.2V application schematic
You guys are 100% percent correct, my calculations were based on dynamic power, however I never considered what happens if I ran the core continuously with some lengthy floating point computations
I I will settle for a buck then, that ST1S10 looks nice and simple (thanks!), however now im spoiled for choice
maybe a dual (with integrated FETS) 1.1v @2A, and 3.3V @ 1A will be better, I can then eliminate my 3.3V LDO and slip one solution..