The LM2575 is not a drop-in substitute -- it is a switching regulator controller, just one component of a switching regulator. You still need to add an inductor, diode, and capacitors around it, and route it properly on a PCB to keep the switching loop tight, etc.
The data sheet makes it clear what extra components are required.
Just be aware that building a DC / DC converter is not simply a matter of putting the parts round it. It requires a PCB with a very critical layout requirement.
The datasheet suggests that ......
The point I am making is not that it is imposable to make your own it is just that it is not easy to get it right first time. Better men than me have failed at that.