STM32L082KZ ADC load resistance

[JWeij.1]

I am trying to create a voltage divider to read a battery voltage of 2.5 - 3.8 V using a STM32L082KZ with a Vref of 1.8V. While calculating the required division to measure the range i wanted to include the influence the ADC measurement/loading has on my division but am unable to find a specification that shows this value.

 

My question is, how high is the ADC resistance loading? I can see it is a SAR ADC so i would expect only parasitic resistance, but is this in the order of tens of kilo ohms or mega ohms?

[TDK]

Generally, it's on the order of 50 kOhm, but it depends.

If you are sampling quickly, it can be much less.

See details in the datasheet.

stm32l082kb.pdf

[STOne-32]

Dear @JWeij.1  @TDK 

infomation is inside our datasheets and in particular in your case the impacting factor is the internal leakage as you are measuring a static voltage of battery that change very slowly. figure 29 - in range of 50nA ..

then you can put and select your right resistance values to minimize battery draw and have good accuracy of measurement.

Hope it helps you 

STOne-32