This code will export the current map as a dwg of the same name as the current drawing, but with "_FDO" appended. It saves the new drawing to the same folder as the current drawing. You might want to remove the alert. I put it there so the user will be told what file is being saved, but it's not critical. And, of course, you will want to change my c:whatever nomenclature to a name that makes sense to you.
Is this what you were looking to do? If you don't know how to put this on a button, read up on the CUI, including how to create a new command and how to add a command to a ribbon panel.
Tim Corey, Owner Delta Engineering Systems Redding, CA Autodesk Authorized Value-Added Reseller