Know the ADC vRef? For ADC LSB to mV ratio


#1

What is the ADC input vRef voltage?

Spec sheet (https://raw.github.com/spark/core/master/Datasheets/ST_STM32F103CB.pdf) says between 2.4 and the actual Vdda / VIN with a max of 3.6v.

This matters as the spec sheet calls out the ADC divides up it’s LSBs based on the “ideal” formula of vRef / 4096. I’m taking that with a shaker full of salt as most of the TI range of ADCs don’t have a self correcting vREF external reference, ADS1119 is a new example of one that does.

Knowing the theoretical LSB / mV ratio (with gain/offset calcs) makes it easier to map exactly the ADC result to mV and then to resistance for temperature sensing.


#2

Are you refering to a particular Particle device?
For Core, Photon and Electron Vref is the output voltage of the onboard 3.3V regulator.
For calibration you can measure the 3v3 voltage and insert that into your calculations.


#3

Hah! Thanks ScruffR. Brain fart. For some reason I thought the P1 had an internal LDO, I should have checked the functional diagram on the datasheet. As you say, I can just validate that my external LDO is actually 3.30v