Hi there,
We use a STM32F777VIT6 in our application.
We tried to use the internal ADC to monitor the voltage of the backup battery.
In principle, this works, but we noticed two effects that we cannot explain.
The data sheet for the STM32F7 states that VBAT on the ADC is divided by an internal 1/3 voltage divider. But it turns out that the ratio 1/4 must be used to calculate the correct voltage. In addition, if the VBAT pin is pulled to ground, approximately 0.8 volts are still measured. However, other voltages such as 2 volts are measured correctly.
Why is the voltage division ratio different than in the data sheet and why are the 0 volts measured as 0.8 volts? Are we doing something fundamentally wrong here?
The F777 data sheets shows a ratio of 1/4 from what I see. Perhaps you have an outdated version? Or another chip?
The VBAT measurement has a minimum sampling duration of 5 us. Are you satisfying that? Use the largest sampling time possible for the most accurate result.
