STM32 gotchas
209.ADC/DAC readings don't correspond to VREFBUF setting, due to VREF+ being connected to external voltage source

While the internal reference VREFINT present in all STM32 is not usable as direct ADC (or other analog functionality) reference, newer STM32 families have an internal reference source with a buffer, VREFBUF, which can be used in such capacity.

Many users don't realize, that even in those families, it's still the VREF+ pin which is the ADC reference input, and that the VREFBUF output is connected directly to VREF+ pin. This has several consequences:

In most boards like Nucleo or Disco, VREF+ is connected to VDDA, either directly or through a solder bridge/resistor/jumper. If a user unaware of the latter requirement uses such board, the ADC outputs values which are surprisingly different (usually lower) than what would be expected due to the VREFBUF setting.

In a certain way, this is an opposite case to g208; but the corollary is the same: always start with checking VREF+ when using ADC (or other analog functionality).