Switcher pre-regulator + LDO or just switcher?

[shadewind]

I'm powering an ARM MCU (TI/Luminary LQFP thingie, among some other things) from 9V - 12V (somewhere around there) and I'm wondering what the best way is to do this. My first thought was to simply use an LM2675-3.3 switcher to simply bring that down to 3.3V. But then I'm starting to think I might want +5V on the board as well.

Is using an LM2675-5.0 for the +5V and then an LDO to 3.3V a good idea for this? If so, any LDO you can recommend? If I didn't want 5V, would there still be a point in using an LDO for cleaner power for the MCU?

[Simon]

5t all depends on the conversion efficiency you require and the current draw, if you only need a few mA at 5V then just use a regular linear reg from the 9/12V supply. more information will help make a better recommendation on your supply "logistics"

[AdShea]

Do you have analog stuff on any of the rails?  If so, I'd usually use a linear regulator and a few ferrites for those rails.

[Zero999]

Yes, it depends on what you're doing.

Where are you getting 12V from? If it's an automotive system and only powered when the engine is running and you need under 0.5A from both 3.3V and 5V, you might as well just use a linear regulator for the whole thing.