IR3315 input control grounding?
The short answer is yes you can just ground the IN pin. As the last paragraph states 

As previously mentioned in the datasheet, Ifb is proportional to the power mosfet current. Thus you can assume it to be a current source. As the quote says, shutdown is the difference between the two voltages, so you can say whatever voltage you set your input control to is essentially a local ground to the current sense side of things. As the current increases, Vifb (=Ifb * Rifb + Vin)will increase until Vifb-Vin>4.7V and the entire thing turns off.

By this you can set Vinput_control to whatever voltage you want, specifically the one that will allow Vcc-Vin > 6 V (or whatever Vih actually is for your device). If 6 V is your desired turn on voltage than grounding them would work.

Finally, I hope that this is a logical exercise, or that you eventually want to use the current sense side of things, because this chip is more expensive than a PTC fuse, requires more components, and clearly is more complicated :)