I want to use an STM32F0x to interface a i2c sensor via USB. Reading the sensor is triggered by an interrupt.

If I don't do any ADC I should be fine with connecting VDD and VDDA right?

I know this reference circuit for separate VDD and VDDA. How would this look if I connect them to the same source? Will I just bridge VDD and VDDA and keep all 5 caps in parallel or would I change something here?

enter image description here

STM also recommends to use an external filter circuit if VDD and VDDA are connected. I guess this is just adds an inductor between VDDA and the decoupling capacitors?!

For my application this should also not be necessary.


1 Answer 1


Normally, there's no problem with shorting VDD and VDDA. But there are few things to consider:

  • I don't know what the actual MCU you use is but for most of them, AFAIK, even if you are not using ADC or related blocks, VDDA should always be greater than or equal to VDD (VDD ≤ VDDA ≤ 3.6V) and VDD can't be no more than 400 mV greater than VDDA. It's also a requirement for the MCU to see VDDA first before VDD during POR (power-on reset). Shorting them will probably ensure these.
  • If you have to use same rail for both VDD and VDDA, it's always good to provide a separate path for VDDA in order for the ADC to use a cleaner supply (If you don't use ADC it can be omitted):


simulate this circuit – Schematic created using CircuitLab

  • 1
    \$\begingroup\$ Depending on what you are doing, filtering VDDA may be a good idea, since there are many other important blocks inside the MCU than just the ADC that use the VDDA. For example, all the internal oscillators, supply supervisors, DAC, and comparator circuits depend on stable VDDA. \$\endgroup\$
    – Justme
    Oct 20, 2023 at 9:08

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