I'm making a K60, TQFP144 board with ethernet, SD card and a whole lot of other stuff that uses 3.3V. I need to power the MCU from a 12V battery (let's say range 10 - 14.4V). Most of the time, board will be in power down mode, where I would like to have the power consumption under 100uA. The board needs to be able to wake-up by it self regularly (let's say a few times a day). My problem is designing a power supply for the MCU.
In very low leakage modes the MCU burns a few uA, so that would suggest a low power LDO from 12V to 3.3V. But at run mode, it can consume about 100mA, which is too much for any low power LDO, hence a buck converter should be used. I could use both, but switching between the two would not be easy. I could use a buck and a LDO and two diodes, but that would make the 3.3V line poorly regulated; and I don't want that. A solution is also to use an auxilary KL05 MCU , powered by a LDO, to turn on the buck converter for the K60, but that kinda complicates things too much.
Can anyone suggest a power supply solution for my situation?
Thanks in advance