Asynchronous Post Back on TextBox TextChanged

I have an update panel and I want to trigger asynchronous TextChanged event from TextBox. If I add event handler to TextBox, set AutoPostBack="true" and TextBox ID to Triggers in Update Panel, then nothing is happening.

<asp:TextBox ID="TextBox1" runat="server" OnTextChanged="TextBox1_TextChanged" Width="250px" AutoCompleteType="none" AutoPostBack="true"></asp:TextBox><asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="conditional" ChildrenAsTriggers="false"><Triggers><asp:AsyncPostBackTrigger ControlID="TextBox1" /></Triggers><ContentTemplate>
         ...</ContentTemplate></asp:UpdatePanel>

I found to way to accomplish my task with hidden button, but it doesn't look like right solution. Am I missing something?