Can VREF+ be zero?

turboscrew · ‎2021-06-02

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?

turboscrew · ‎2021-06-07

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. "

View solution in original post

Javier1 · ‎2021-06-03

~~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

we dont need to firmware by ourselves, lets talk

Imen GH · ‎2021-06-03

Hello,

It is a working condition for ADC conversions.

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

Imen

waclawek.jan · ‎2021-06-03

> 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

waclawek.jan · ‎2021-06-03

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 · ‎2021-06-03

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.

turboscrew · ‎2021-06-03

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

Imen GH · ‎2021-06-03

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

turboscrew · ‎2021-06-04

I'm really not sure, but I think, when a PSU is turned off, the output gets grounded. Especially when the output of that PSU is fed to a linear regulator whose output is connected to VREF+.

I'd be interested in both cases.

Imen GH · ‎2021-06-04

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