STM32L476VCT6 VREF connection

[Alex_7777]

Hello!

In my project I'm using STM32L476VCT6. I don't want to connect external voltage reference, only internal. Could I leave floating pins VREF- and VREF +?  I saw in the datasheet that these pins could be tied internally to Vdda and Vssa correspondingly. 

[RomainR.]

Hello @Alex_7777 

If you plan to use internal VREFBUF as analog internal reference voltage for ADC or DAC, the VREF+ pin must not be connected to VDDA. Only an external capacitor of 1 μF (typical) must be connected on this pin.
The device you are using expose VREF+ on pin 21 and let you the choice to use external or internal reference.
On smaller package (LQFP64 and below) the VREF+/VREF- are not present, therefore they are connected to VDDA (VREF+) and VSSA (VREF-) internally. You cannot use the internal VREFBUF.
You can refer to the following application note:
https://www.st.com/resource/en/application_note/an4555-getting-started-with-stm32l4-series-and-stm32l4-series-hardware-development-stmicroelectronics.pdf

https://www.st.com/resource/en/application_note/an5690-vrefbuf-peripheral-applications-and-trimming-technique-stmicroelectronics.pdf

Let me know if it helps and answers to your question?

BR
romain

[Alex_7777]

Hello Romain!

could you please let me know should I tie REF- to GND or I can leave this floating for my package (100-LQFP)? 

[RomainR. · Accepted solution]

VREF- must be connected to VSSA (to GND as well), as explained in AN4555 Figure 3:

And the reference design for LQFP144.

BR,
Romain,