So I was playing around with an ATTiny 13a and noticed in the datasheet that, at 2Vin and 1MHz, the supply current is a Maximum of 350uA.

If one uses an ultra-low dropout regulator, say the STLQ50 @ 3uA Iq and 400mV Vdo @ >25mA, not counting any other components in the circuit, that's a whopping maximum 353uA draw, and even less with the Tiny in Sleep/Power-down mode. Changing components/voltages slightly would probably result in no more than 5-600uA unless some really bad choices were made!

Do LDOs suffer at these ultra low power levels? I've never considered the question until now, everyone is typically concerned with maximums...

I know some SMPS ICs will lose efficiency drastically at the low end of their current range, even those with PFM, is there any similar phenomenon with LDO's at supply currents in the hundreds of microamp range? It seems to me that the dropout voltage would be ultra-low at those levels, but I am only speculating?

Can anyone speak to this?

TIA, Cheers!