voltage regulator - How to choose the transistor and the resistors connected to it

I am using the regulator TL497 in the case of I(pk)>500mA so I need an external transistor for that but in the datasheet they don't mention how to choose the transistor and its resistors does anyone has an idea about that ? Datasheet:http://www.mouser.com/ds/2/405/tl497a-405896.pdf