high voltage monitoring for AD8212

Hi there,

I have some question's about AD8212 for monitoring high voltage.

According to the datasheet, it says that "7 V to >500 V with external pass transistor ".

#1,Why is the common voltage  limited upt to >500V ?

#2,Is it possible to use this device to monitor high voltage like 1500V?

If it's okay, what designer should consider?

And the datasheet example is using PNP transistor.

#3,Instead of PNP transistor,does the circuit work when Nch-IGBT like GT40WR21 is used?

Thanks in advance.

Best regards,