<asp:TextBox ID="txtDate" runat="server" AutoPostBack="true" OnTextChanged="txtDate_TextChanged"></asp:TextBox>
<asp:CalendarExtender ID="txtDate_CalendarExtender" runat="server" Enabled="True"
TargetControlID="txtDate" Format="dd.MM.yyyy">
</asp:CalendarExtender>

i am using Calendarextender and i OnTextChanged event. In C# code (Page_Load) i am calling

txtDate.Text = DateTime.Today.ToShortDateString();

becouse of this i get postback after page is loaded (page is loaded 2 times). How can i prevent postbak in calendar extender after page is loaded for first time?