ADC stability

[kkhli.1]

"I used the STM32F746ZG to read the current from an ACS712 sensor, but the problem is that the ADC is not stable. I tried using an STM32F466RE to measure the same current, and this time the ADC is stable. I don't understand why, despite the ADC characteristics of the two STM32 being similar. Is there an explanation for this?"please see the two images below

[AScha.3]

ADC is not stable ... did you calibrate adc first ? ( HAL_ADCEx_Calibration_Start(...) )

+

set same/similar sampling time and conversion speed ?

[kkhli.1]

yes i setted the same sampling time 480 cycle with ADCCLOCK 36 MHz

i did not calibrate the adc  because i do no how , i tryed to call HAL_ADCEx_Calibration_Start but i did not found this in hal librarry 

[AScha.3]

just look at ..Drivers/STM32Fxx_HAL_Driver/Src/stm32h7xx_hal_adc_ex.c

-- what is there..with xxxcalibrat...

(some series have auto-calibration at start , most not -> then you need to call calibration for adc running as it should. )

 

[raptorhal2]

Just in case the problem is some unknown effect of the F7 interacting with the sensor board, try the Application 7 noise attenuation method provided in the ACS712 data sheet page 13.

As a further note to Ascha's response, the ACS712 has a low impedance op amp output. Large (480) sampling cycles should not be required, his 15 or 28 cycles likely all that is required.