I'm looking at (the millions of) buck regulators available for a project where the board will be a host board for a Gumstix Dual Cortex A9. This can pull quite a bit of current at maximum so I was figuring 2.5A for a good bit of leeway. However it will also be battery powered so, assuming I can get the Gumstix and the rest of the equipment to sleep efficiently, the quiescent current of the regulator becomes important.
I was thinking that would mean I should use a non-synchronous regulator as, traditionally, the synchronous have been poor in low current modes. The non-sync can operate in Discontinous Current Mode due to the freewheeling diode, which the sync can't do. However, there seems to be synchronous regulators that can do it all. Looking at the LT8610 from Linear, it has high efficiency at high power and high efficiency at low power. It achieves this by using "Burst Mode" at low currents. Apparantly down to 2.5uA which is quite something.
My concern is that there may be a catch. I believe various Burst Modes can lead to chirping - that irritating squeak that comes from the bursting on-off frequency causing the capacitors/inductors to vibrate at audible frequencies. I used to hear that quite a lot, mainly from laptops, and I don't really want the same thing in my project.
The other catch of course is that the LT8610 is nearly twice the cost of a simple non-synchronous regulator like a TPS5420 and is harder to work with (16 pin MSOP vs 8 pin SOIC). I can deal with that if it's has nice features.
It is somewhat mystifying how systems like the Kindle manage to be in sleep mode to the extent that they are. Perhaps they use linear regulators... or some sort of combination