I am required to design a circuit which regulate the voltage (3.3v) coming for a Master microcontroller pin to not more than 3v and restrict the current to 2uA. This in order to fulfill safety circuit constrains, then the output has to power on a slave Microcontroller which most of the time will be in sleep mode and will wake up about every 200ms do few tasks and go back to sleep again.
So far I have this circuit using Zener diodes with 3v breakdown voltage, having ~2uA across R2.
There is no problem to operate the slave microcontroller in sleep mode with this current because I have chosen the EFM8SB2 "sleepy bee" with the following features:
The problem is in the active mode where I require minimum 170uA. Since the microcontroller will be in active mode max every 200ms for a really short time (only send 8 bits to master and read a value from an odometer magnetic sensor ) I though about a capacitor which would charge while the microcontroller is in sleep mode and discharge when the microcontroller is active mode to provide enough power to operate.
My first question is. Is it actually realistic to go for this approach? If so, how would the circuit design looks like?Perhaps I have to use sort of a switch to change from the sleep mode to active mode configuration.
I have read about the charge-pump approach but I do not know if that would be the solution for my problem.
I would really appreciate any hint or references about this matter.