STM32H747 ADC reading isuue

[SPate.11]

Hi STM team,

We are using stm32h747, with CM7 we are reading ADC value in polling mode, when source is not conneted still we are reading 0.5 to 1.8 volts, when the temperature increases from 40 C to 60 C this ADC voltage reading increase with rise in temperature till 14V. 

We have also try to do ADC calibration on every 5 degree rise in temperature but still we are reading ADC voltage value where it should be near 0V as the ADC input was not connected.

 

Regards,

Snehal

[mƎALLEm]

Hello,

If you intend by "when source is not connected" : keeping ADC input floating ... is not a good idea and you don't expect to have 0 V as a reading value!

[SPate.11]

Hi There,

We are working on a locomotive control system where we have the main supply and backup supply, we are monitoring these supplies using ADC. 

In this particular case when where there is no input to ADC we observed a very high 14V voltage, ideally it should be 0V but in a practical scenario some minor leakage or noise on ADC reading between 0 to 1V is acceptable.

schematic point of view this ADC pin is not floating when there is no input, below is the portion of the schematic, 24V_0_MON connected to ADC3_INP9 (PF4) pin of STM32H747.

We also try to add filter capacitors across R54 and R55 but that is not helping.

 

Regards,

Snehal

[mƎALLEm]

Hello,

Did you test with just a DC source (0 to VREF) connected directly to the ADC input and see what happens?