ASP.Net AJAX UpdatePanel does postback twice

I have a page on which there is a textbox that is in update panel and has text changed event and autopostback=true. On the same page there is a 'Retrieve' button(inside repeater control) outside the updatepanel. Now what is happening is if user inputs data in the textbox and clicks retreive button page_load event is firing twice which is not what should be happening, one time its the partial postback due to the text changed event and second time is the page post back. I would like to restrict the second postback.