Verpflichtungserklärung needed or not?

[Schickelgruber]

Hey guys.

I am going to Germany in December and I have all my papers in order. I am going to be staying with my uncle at his own house but he is not covering my trip financially. I have sufficient funds to travel and afford the holiday.

Do I need a Verpflichtungserklärung or will an informal letter from my uncle be enough? Since he is not paying for my ticket etc..

URGENT HELP GUYS!