The current rating of the part cannot be extended by using an external mosfet.
The current is limited or set by resistance across the SETI pin. The resistance value should be chosen less than 6kohm correponding to 6.3A (resistance vs current values are mentioned in page18 of the datasheet).
The part has some internal logic drive circuits and a maximum power dissipation limit that could be exceeded through external components, violating the recommendations made in the datasheet.