Hi Dan,
PVIN is the supply for the powerstage, while VIN is the supply for the rest of the IC. In the real device this is done to minimize the effect of switching noise on other circuitry. In the model it does not matter if the PVIN and VIN pins are connected together since all the voltage sources are ideal.
If you would still like to, you can connect PVIN and VIN pins to two different voltage sources. Hope that answers your question.
Regards,
Lakshmi