External voltage reference on Nucleo-F072RB

[Teun888]

Hi,
I wanted to use an external voltage reference of +2.048V on the Nucleo Board. To do so I removed SB57 as dictated in UM1724 document: 
SB57 (VDDA/VREF+)
ON VDDA/VREF+ on STM32 is connected to VDD.
OFF VDDA/VREF+ on STM32 is not connected to VDD and can be provided from
pin 8 of CN5 (Used for external VREF+ provided by ARDUINO® shield)

The Absolute Maximum Ratings for STM32F072xB (table 21) give the following:
VDD–VDDA Allowed voltage difference for VDD > VDDA - 0.4 V

Does this mean I am bound to a 3.3V reference and can not use lower voltages?

On Arduino boards these normally accept other voltages.

[MasterT]

It says on front page:

Digital and I/O supply: VDD = 2.0 V to 3.6 V
– Analog supply: VDDA = VDD to 3.6 V
And page 14

The VDDA voltage level must be always greater or equal to the VDD voltage level and must be established first.

https://www.st.com/resource/en/datasheet/stm32f072c8.pdf 

Choose another nucleo, like nucleo-G474re 

[Andrew Neil]

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@MasterT wrote:

The VDDA voltage level must be always greater or equal to the VDD voltage level and must be established first.

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Note that the "must be established first (sic)" is a bit misleading: 

STM32F030 datasheet: Misleading VDDA vs VDD sequencing description?

[Andrew Neil]

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@Teun888 wrote:

On Arduino boards these normally accept other voltages.

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Well, Arduino boards are not STM32-based - the requirements of their various microcontrollers may well be different.

In particular, many Arduinos are 5V - not 3V

Or are you talking about the IOREF or AREF pins on the shields ?

[Ozone]

I think you need to check the schematics again, and the DS and pinout of the specific package (I don't know the F072 Nucleo).
You most probably want separate VDDA and VRef pins, which not all packages have.
Smaller ones have only VDD and VDDA separate, with VRef is derived from VDDA.

And the tiny packages like TSSOP20 have only one single pin for VDD and VDDA.

Many smaller Nucleos use QFP32 packages, with no separate VRef pin.

[TDK]

> Does this mean I am bound to a 3.3V reference and can not use lower voltages?

For this chip, yes. Other STM32 are more lenient.