I designed and built an analogue processing circuit for measuring power quality. I believe I made some mistakes when setting up the system's power supplies and i'm looking for some advice or general standard on what to do in this situation.
The system is running off batteries (4xAA), so over time, the supply voltage drops below the minimum needed voltage. So, I placed a centralized buck-boost to provide a stable system voltage and hooked the rest of the system supplies to the buck-boost. Below is the system supplies:
As the circuit is doing percise measurement; percision LDO's where used for ADC and offset voltages (drawing a couple of mA). What I found is the Buck-Boost switching noise was leaking into the LDO's outputs (be it Microvolts - but this damaged system sensitivity). Mistakabily, I hooked up an STM32 MCU (using about 50-100mA) to the buck as well causing system strain and leaked MCU noise into thte system.
My question - with the given 'Vout' voltages required and the supply varying from 6-4V, what would be the best practice - separating precision and the (relatively) high power supplies? I was originally thinking if I supplied the MCU separately, I would be attenuating 6V to 3.3V, burning lots of power and requiring a beefier MCU supply to handle this. Advice?