STM32L011F4 drooping supply rail where as STM32L031F6 doesn't on the same board

[kudale]

Hey,

I am using STM32L011F4 with an external ADC & DAC connected via SPI bus.

I have 3.3V & 5V rails on the board, 5V regulator (internal to an IC) can only supply 10mA max current.

Controller when unprogrammed droops the 3.3V & 5V rail. If powered externally i.e. higher current capacity, the controller gets programmed and works as expected with no issue even after removing the external power source i.e. no longer droops the rails.

Removing ADC when controller is unprogrammed also solves the issue or keeping the ADC and removing the controller also solves the issue (rail drooping issue).

When the controller replaced with STM32L031F6 also solves the issue.

Has anyone faced this issue or can help me understand why this might be happening?

[waclawek.jan]

Sounds like ADC pins "fighting" with mcu or DAC pins - maybe ADC or DAC chipselect is not driven properly?

JW

[kudale]

....

[kudale]

Yeah there are no pull up or pull downs on the chip selects pins but I have similar circuit on other board which works fine without pull up or pull down.

And as the voltage is drooping I am unable to program the microcontroller