Backspace not working on Input tag

I have an Input tag of type "Text" where I want the user to enter only in uppercase , hence I am using liveChange event for this. But for some reason, the backspace on the keypad is not working. Not able to understand why.

    <Input

                liveChange="handleChange"

                id="userName"

                type="Text" />   

    handleChange : function(){

  var userName=this.getView().byId("userName").getValue();

  userName=userName.toUpperCase();

    this.getView().byId("userName").setValue(userName);

  }

Please help. Thanks