Alternatively we can use Rj from the same graph, to can calculate maximum power dissipation at room temperature:
Pdmax = (Tjmax - Ta) / Rja = (175C - 25C) / 100 = 1.5WImax = Pdmax / Vdrop = 1.5W / (12V-5V) = 214mA
Personally I have been able to draw up 250mA through the regulator before it started shutting down, which matches the above math.
Do you know how hot 175 degC is? You're talking about the outer limits here. That's
why I mentioned "getting rather hot". I still think 0.5W is a more reasonable value.
The obvious way to increase loading capability is to use a lower value of Vin. With
Vin = 7V, 250 mA is more realistic.