Well, the internal temperature sensor is based on a pn junction through which a constant current flows and whose temperature coefficient of approx. -2mV/K is used to determine the current chip temperature. However, even after calibration, its accuracy cannot be compared with that of an external temperature sensor.
Depending on your requirements for "precise temperature measurement", an external sensor may be the only option, or alternatively the STM32G071, whose value is measured for TS_CAL2.
Regards
/Peter
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