I'm looking for a movie from the old series "DuckTales".

The only thing I can remember is that Scrooge, Donald and his nephews where looking for a Mayan city. They had a gold coin similar to the gold coin from Pirates of the Caribbean, except that this one didn't had a skull, it had a sun.

Anyone knows the name of that movie?

Sounds like part of the pilot, collectively titled "The treasure of the Golden Suns"

Treasure of the Golden Suns Season Episode Guide on TV.com