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turboscrew
turboscrew
Senior III
June 3, 2021
Solved

Can VREF+ be zero?

  • June 3, 2021
  • 14 replies
  • 3334 views

In STM32F437 data sheet it says VDDA - VREF+ < 1.2 V.

Is that a "global" limitation or just a working limitation?

If VDDA is 3.3V and VREF+ is 0V, can that harm the chip, or is it just that the conversions don't work right?

This topic has been closed for replies.
Best answer by turboscrew

OK. Our client got the answer from STM in another way.

"I confirm VREF+ could be grounded when ADC and DAC are not active but you need to make sure that the VREF is stabilized before to start the ADC conversion. About VDDA should be connected as soon you have VDDa pin on the MCU because it is the power supply for all the analogue parts of the MCU - Reset blocks, RCs and PLL. "

14 replies

Javier1
Javier1
Principal
June 3, 2021

You could disable VREF pin i believe... (never done it myself)

Looks like you cannot:

@Community member​ >You cannot disable the connection between VREF+ pin and the analog circuitry which uses it (ADC/DAC).

HALD_ADCEx_EnableVREFINT()

Similar topic question

https://community.st.com/s/question/0D50X00009XkWMj/vref-output-for-external-ic

hit me up in https://www.linkedin.com/in/javiermuñoz/
Imen GH
Imen GH
ST Employee
June 3, 2021

Hello,

It is a working condition for ADC conversions.

On your side, will you use analog  peripherals (ADC or DAC)? 

Imen

turboscrew
turboscrewAuthor
Senior III
June 3, 2021

Yes, but for sleeping, I'd like to turn the VREF+ voltage off. It doesn't come from the same power as VDDA, but a different better regulated power.

That same power is used by some other devices that are monitored with the ADC.

Imen GH
Imen GH
ST Employee
June 3, 2021

The VREF pin is kept as floating or if it is really connected to GND?  

waclawek.jan
waclawek.jan
Super User
June 3, 2021

> You could disable VREF pin i believe...

You cannot disable the connection between VREF+ pin and the analog circuitry which uses it (ADC/DAC).

That Cube/HAL function presumably disables the connection between internal VREFBUF and VREF+ pin. There's no VREFBUF in 'F4, though; that function is available only for some newer families.

JW

turboscrew
turboscrewAuthor
Senior III
June 3, 2021

I have some kind of memory trace that it selects the reference for the internal channels: Vbat and temp.

Imen GH
Imen GH
ST Employee
June 4, 2021

Could you please give us the device number for the reference voltage generator, just for checking 

waclawek.jan
waclawek.jan
Super User
June 3, 2021

Hi Imen,

> It is a working condition for ADC conversions.

So, does this mean that there is no damage to the chip, if VREF+ = 0V?

Can this fact please be explicitly stated in the datasheets of all related STM32 (i.e. at least all STM32F4xx)?

Thanks,

Jan

@Imen GH​ 

turboscrew
turboscrewAuthor
Senior III
June 5, 2021

I guess I need to add the second "like" textually.

turboscrew
turboscrewAuthorBest answer
Senior III
June 8, 2021

OK. Our client got the answer from STM in another way.

"I confirm VREF+ could be grounded when ADC and DAC are not active but you need to make sure that the VREF is stabilized before to start the ADC conversion. About VDDA should be connected as soon you have VDDa pin on the MCU because it is the power supply for all the analogue parts of the MCU - Reset blocks, RCs and PLL. "

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