My question is whether it's reasonable to expect reliable MCU operation with the supply voltage going from a minimum of say 2.7V to 5V, and then back, or is this just a Very Bad Idea?
I'd clock the MCU at 8MHz so it was always in the safe operating area regardless of Vcc.
if the transient is not too bad, it should work.i would, however, split the rail: using the 2.7v to power the mcu and the dc/dc converter for the 5v device.
I would think it should work ok. The only caveat I can think of is that the brown out voltage detector reset might have to be disabled or set to a value lower then 2.7?
I can't think of anything in the datasheet that contradicts what you want to do. Seems like a good idea to me.
If the processor will spend anytime polling 1 MHz (or even 128 KHz) may be a better choice.
Certainly the battery will have some juice left at 2.7V, so it may be worth trying 1.8V.
QuoteIf the processor will spend anytime polling 1 MHz (or even 128 KHz) may be a better choice.Probably not much if any, but are you thinking more from a power conservation standpoint, or immunity to the Vcc fluctuation?
The Rayovac alkaline batteries I've been using have enough life down to 0.8 volts (each times 2 batteries for 1.6V) to keep an ATtiny85 running reliably. In other words, I believe 1.8V is a good threshold for AA alkaline batteries.
so there are now two of those in my fridge
but then I may have to level shift signals between the MCU and sensors, I'd prefer to avoid that if possible.
Quotebut then I may have to level shift signals between the MCU and sensors, I'd prefer to avoid that if possible.Put a pull-up resistor there.