It's impossible. For the low-speed oscillation frequency, the built-in temperature sensor is A/D converted with the internal reference voltage (about 1.55V), and that value is used for correction. In addition, table data etc. are created based on the internal reference voltage (about 1.55V). Therefore, if you change the voltage input from the VREF pin or VDD as a reference, the A/D conversion value of the temperature sensor will change and the correction will not be normal.
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