I have always used just a battery and a LDO in applications where noise is inportant but obviously battery and LDO means really awful battery life and low effeciency overall.
I would like to implement a switching pre regulator , followed by a filter (ferrites and capacitors) and then the LDO. I have searched quite a bit on google but didn't find anything other than control the output of the regulator with something like a dac or digital pot but that's not ideal.
Is there a way to have the output of the LDO in the feedback loop of the pre regulator so adjusting the output of the LDO, automatically adjusts the switching regulator?