Suggestion for discrete isolator between input and MCU

[FreshmanNewbie]

I have the below attached circuit where, the input voltage is voltage divided and given to the ADC input of the MCU. MCU is powered from 3.3V.
3.3V power for the MCU is also obtained by stepping down VIN to 3.3V using buck converter.

Before the 3.3V comes to the MCU, there might a leakage from this voltage divided VIN and through the ADC input pin of the MCU, through it's ESD diode and to the MCU's 3.3V rail.

Can anyone suggest a simple isolation technique to avoid the above?

 

[danadakk]

The current is so low. eg. the 470K limiting it, why do you care ?

To isolate you would have to open the path with a switch of some sort, like
a MOSFET or JFET.


Regards, Dana.

 

[KlausST]

Hi,

as Dana says .. it is a little current. Did you calculate this current? If not, do so!
Then compare this current to the maximum allowed ESD diode current (may be named differently) of your microcontroller. You need to read it´s datatsheet.
We did not get a link to it ... for a detailed discussion, nor do we hav any information about the microcontroller.

Then you say "Before" .. what does this mean? What range of time do you speak about?
What range is VIN?

So we don´t know: timing, VIN range, microcontroller type, expected accuracy, other requirements (example: max additional current drawn from VIN and 3V3)... or whatever is important ...

**
Side information:
I expect the measurement rather inaccurate because of
* high impedance resistive divider (read microcontroller datasheet)
* I guess you "compare" against an inaccurate VCC

Klaus

 

[FreshmanNewbie]

The current is so low. eg. the 470K limiting it, why do you care ?

To isolate you would have to open the path with a switch of some sort, like
a MOSFET or JFET.


Regards, Dana.

If I use a MOSFET, I need to give the Gate control signal from the MCU, correct?

 

[danadakk]

If I use a MOSFET, I need to give the Gate control signal from the MCU, correct?

Yes

Prior question asked of you -

The current is so low. eg. the 470K limiting it, why do you care ?