Many of the recent Microchip PIC power-on-resets use a digital counter internally. I'm guessing that they're working within confines similar to what you have and also they're trying to keep power consumption while asleep to a minimum and deal with brownout recovery. I don't know the details but they must be taking on-chip clock in the 10's or
100's of kHz to tick everything along.What requirements do you have regarding power consumption while asleep, brownout recovery, ?
Tim.