How to get Vrefint out from STM32F334 for precision temperature measurement with RTD ?

[Manu Abraham]

Hi,

Looking at

http://ww1.microchip.com/downloads/en/appnotes/00687c.pdf

to implement a RTD temperature sensor and the onboard ADC on the STM32F334, trying to get the ADC Vref out to the constant current generator opamp. I can use an external Vref for the RTD current, but then that would not be in sync with the ADC reference.

So, the proper solution is to use a common Voltage reference for the Current Source as well as the ADC.

I have the following 2 options:

(1) Use the STM32F334 internal Vref and an external unity gain buffer, as a reference for the constant current source.

(2) Use an external precision reference as a reference for both the ADC and the Current source.

Option (1) seems to be a better choice, but I am struggling to think of an option how to get Vrefint out. Even option (2) is viable, but then it does not appear to be possible to provide any external reference to the STM32F334. Or is it possible ?

I would like to know what you folks think about it.

Thanks,

Manu

[Uwe Bonnes]

Provide VDDA by an external reference as analog supply and reference. I do this to evaluate PT1000 sensors. I use a good 1k resistor to VDDA connected to the PT1000 , with the PT1000 connected to ground and use the PT1000 voltage buffered by an 100n capacitor direct as input to the ADC. I add some measurements for noise reduction. Calculating with the well known PT formulas and testing against another 1k resistor, typical error is below 2 Kelvin and values are stable within 20 milliKelvin.

[Manu Abraham]

Hi Uwe,

Thanks for the pointer. What external reference do you suggest and the voltage ?

Cheers,

Manu