Cool thread, let me put my 2 cents:
In Puma, there is a SMPS to step down vbat to 5.75v. This way, regulators doesn't get hot, and they (or at least the big one) attenuate the SMPS ripple by 30dB or more. Its capable of handling 30v inputs, but I can't see if it can work at 1 or 2 mA loads. Also, I have the *impression* that switching things shouldn't be supplying analog circuitry or sensors, but its mostly a prejudice.
Unfortunately, input voltage can't be under the specified output voltage (5.75v). That output voltage could be lower, though.
btw, design considerations demand to have 2 sources of 5v, at least on boards that follows the "always on" strategy.
This is an app that jharvey has found, and you can see the actual values I'm using
A quite important note:
Simulators like these aren't wise enough to suggest stocked items. I spent some hours with iterations like:
START
does it work?
is it the best combination so far?
are components available? -> yes -> DONE (ha! never happened)
are there similar components? -> no -> goto START
| yes
DONE
I checked the components suggested by National, and you have to get them from different distributors. Another restraint was the 85°C temperature limit. Not a big deal, I guess you can pick other components if they are similar enough.
In the original design calculated by ST I got 9mV of ripple. After playing around it went down to 7mv or so (jharvey got 4mV for a 5v output). It was a shame that the output capacitor and inductor weren't available. With similar and available components the best I had was a 14mV ripple at a 14V input (0.24%).
The moral is: keep in mind availability :-)
And, according to simulations, ripple doesn't depend on load, but in input voltage. Power losses are mostly load-dependent.