numericupdown control cannot apply on textbox (AutoPostback=true)

Hi guys, my page will keep refresh if I set AutoPostback = true to my textbox. Please advise. TQ

<asp:DataGrid ID="MyDataGrid" runat="server" DataKeyField="PID"><Columns><asp:TemplateColumn HeaderText="Qty."><ItemTemplate><asp:TextBox ID="txt_quantity" runat="server" Text='<%#Container.DataItem("quantity")%>' AutoPostBack="True" OnTextChanged="QuantityChanged"></asp:TextBox><cc1:numericupdownextender ID="nude_quantity" runat="server" TargetControlID="txt_quantity" width="70" minimum="1" maximum="99" /></ItemTemplate></asp:TemplateColumn></asp:DataGrid>