STM32L4 VREFBUF. Cant select internal 2.5v voltage reference for ADC.

[Scott Dev]

Hi

I am using the STM32L433 100 pin which has the internal 2.5v vref buffer for the ADC. I am getting readings, not accurate, from the adc . Looking at the data sheet the internal vrefbuf is tied directly to the VREF+ pin, and when I measure that pin it is 3v. I am doing the following to select the 2.5v, can any think of what I am doing wrong?

ADC1->CR |= 1 << 28; //enable voltage reference

VREFBUF->CSR = 0b101; //2.5v ref selected and Internal voltage reference enabled

Many Thanks

Scott

[waclawek.jan]

And how do you have pin 21 connected?

JW

[Scott Dev]

I have a jumper where I can select an external 2.5v supply. Its a test board, but would like to use the internal 2.5v reference to reduce chip count.

I also have VDDA to 3.3v, Vref- and VSSA to 0v,

Regards

Scott

[waclawek.jan]

OK so if you have an unprogrammed mcu or you hold in it reset, what do you measure on that pin?

Or, in other words, under what circumstances did you measure 3V on it?

JW

[Scott Dev · Accepted solution]

Its working fine now, I am getting 2.5v on the pin. I dont know what happened when I previously tested it.

Thanks again 🙂

Scott