There is a diagram in the datasheet, specifying the temp. sensor voltage across the temperature range. (Fig.42 at page 142).
The datasheet further says:
The temperature sensor transducer uses an intrinsic pn-junction diode reference and outputs a CTAT voltage (Complement To Absolute Temperature). The output voltage varies inversely with device temperature with an absolute accuracy of better than ±5 °C over the full temperature range (-40 °C to +105 °C). The temperature sensor is only approximately linear with a slight curvature. The output voltage is measured over different ranges of temperatures and fit with linear-least-square lines.
Such p-n voltages use to differ, I suppose the given diagram is an average. So, it seems you need to calibrate it yourself (record the voltage at two or more temperatures). Or check the SDK examples, perhaps there is one for the sensor (check the ADC section).
I use such internal sensors rarely, the junction temperature inside the MCU package is of limited value (auto-heating).
