MOSFET overheats and results in short circuit
With a 4.5V gate drive this MOSFET has a maximum Rds(on) of about 10m\$\Omega\$ at 25°C, perhaps as much as 15m\$\Omega\$ at a safe higher junction temperature. If we use that value, power dissipation can be in the 10W range. See the datasheet. 

That's rather high for such a tiny package and may be virtually impossible to achieve with a reasonable setup. At the reference 50°C/W (see below note as to specifics- that's 1 square inch of 2 ounce copper- not insignificant) it obviously will burn out rather quickly (500°C rise is not going to be possible). At 125°C/W (second layout below) it will probably fry in seconds.  

You need a MOSFET with much lower Rds(on) and/or a MOSFET that is in a package capable of dissipating more power. 

Note that if you're feeling fooled by the datasheet- that is an 'absolute maximum' rating- not something you should be designing to. Constraints often turn out to be other than the first number you run across- in this case it's thermal. All constraints must be simultaneously respected or you may have a bad day. 


  (2) Device mounted on FR4 material with 1-inch2 (6.45-cm2), 2-oz. (0.071-mm thick) Cu.