STM32U575 ADC4 unable to set AUTOFF bit

[Tomas Hamouz]

I am unable to switch on the AUTOFF bit in ADC4.

DS reads about ADC_PWRR/AUTOFF: The software is allowed to write this bit only when ADEN bit is cleared to 0 (this ensures that no conversion is ongoing).

But if this bit is set, the ADC doesn't set ADRDY flag if enabled.

LL_ADC_SetLPModeAutoPowerOff(ADC4, LL_ADC_LP_AUTOPOWEROFF_ENABLE);

LL_ADC_ClearFlag_ADRDY(ADC4);
LL_ADC_Enable(ADC4);

while(!LL_ADC_IsActiveFlag_ADRDY(ADC4)) {}   // here waits forever

If I omit the ADRDY check and simply wait some time and then I start the conversion, the ADC works and converts inputs correctly.

If I omit the AUTOFF setting, the code works ok. If I try to set the bit after enable, the bit remain unchanged (acording to DS)..

My question is: How to set the AUTOFF bit? Isn't it a bug in silicon?

[Amel NASRI]

Hi @Tomas Hamouz,

Coming back to your question, I hope it was solved since the time you asked it. That would be interesting to share your findings.

On my side, I have following 2 proposals:

• did you tried using the HAL driver instead of LL functions?
• In the implementation of ADC_Enable (https://github.com/STMicroelectronics/stm32u5xx_hal_driver/blob/5313c6919f88e8ec4212da91bbe1146d4262d44c/Src/stm32u5xx_hal_adc.c), it continues to enable ADEN until ADRDY becomes 1. Can you make a similar implementation?

-Amel