It is my understanding that the burndown chart is specific to the current sprint, and doesn't apply anywhere else in Scrum. If you are trying to have separate charts for separate teams (or projects), then you are encouraged to create a new team (or a new project) and manage the two separately.
One way to achive this is to (re)structure al the development task in a single project and the rest as a Miscellaneous project then you can see the burndownchart of each project