Battery Sensing on ADC pin ?

[K_P_D]

Hello Every-One,

I am new for Battery sensing & Monitoring.

I am working on the STM32F030 MCU to sense the battery Level on the ADC pin.

Here I need to know the:

1.What is the reference voltage for the ADC pin?

2.What can be resistor value in the voltage divider circuit, if ADC has internal impedance of 50k-ohm(as mentioned in datasheet) with min current drain ? does mega ohm values of divider can match with the impedance with ADC pin.

3.If possible then also share the reference circuit or any reference document for the battery sensing on ADC ?

Thanks

[waclawek.jan]

1. ADC reference input is VREF+ which in many lower-pin-count models is internally connected to VDDA
2. Those 50kOhm is not internal impedance of ADC, the output impedance of your external circuit to achieve the 12-bit resolution. The internal impedance is in megaohms, but if your external circuit will have higher impedance than 50kOhm, that internal impedance will influence the measurement so that its deviation is more than 1/2^12 * VREF+. In other words, the battery sensing divider should be of lower impedance than megaohms and either switchable so that it loads the battery only during measurement, or be of the megaohms impedance but followed by an amplifier (voltage follower) to decrease its output impedance to below 50kOhm.

JW