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wrong temperature measurement STM32U585 when ADC_CR_ADCALLIN is set

martinhaefner9
Associate II

Hello everybody,

i have a strange behavior when doing the linear calibration in ADC1 of the STM32U585.

When the bit is not set while calibrating the ADC the result is pretty good. 
I average the DR value 16 times and the average result is about 3698 which results in a temperature of about 32.21°C

So far so good. Unfortunately when the ADC_CR_CALLIN bit is set the measurement result is "wrong" what means the average is about 1643. The resulting temperature is -142 °C, which is wrong.

 

Anyone an idea why this fails ?

I compared the registers before measurement and they are pretty much the same except the CALLIN bit.

Side note: this is a custom board where VDDA and VREF+ pins are connected to a 3.3V source.

Thanks in advance.

 

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