Why does my DS18B20 not work in external power mode? Connected to Arduino UNO and 3.3V power it heats up but in parasite mode its fine?

The Arduino UNO operates at 5V logic, if the DS18B20 V_DD is connected to 3.3V and Pin DQ is connected directly to the Arduino UNO then damage may occur as these pins need to be within 0.3V of one another at maximum. Connect V_DD to the 5V pin of the Arduino UNO to prevent this issue, or use a 3.3V microcontroller for data and power.