PHPExcel Memory overflow error with CI

[eluser]kissgxd[/eluser]
I'm use CI to build an report application. This application works with Excel, Then I choose PHPExcel To build or read Excel datas. But When my Excel files is larger then 2M,there will be an error occurred like this :Fatal error: Allowed memory size of 209715200 bytes exhausted (tried to allocate 45 bytes) in ...
How can I do ?