The ADT7411 combines a 10-bit temperature-to-digital
converter and a 10-bit 8-channel ADC in a 16-lead QSOP. This includes a band gap temperature sensor...
ADT7411 on Analog.com
The part is trimmed at 2.28V, thus internal reference to use for calculation should be 2.28V.
Moved this Q&A to FAQ's section:
(+) ADT7411: What is the typical internal reference of ADT7411? - Documents - Temperature Sensors - EngineerZone (analog.com)