Web Forms :: Fire OnTextChanged Event For Disabled TextBox

I have 10 text box in a page like txt1,txt2...etc

In text box onchange i call the javascript function

for calculating txt5 value

i.e.

in javascript method,

txt5.value = parseFloat(txt1.value) + parseFloat(txt2.value) + parseFloat(txt3.value) + parseFloat(txt4.value);
and
text box txt5 enabled=false,autopostback is true

protected void txt5_TextChanged(object sender, EventArgs e)    {       // here based on txt5 value i getting records from database and doing some calculation and display those value in txt6,txt7
    }

The problem is the textbox txt5 can;t post back when text change from JavaScript function.

How can I do postback when text box value bind from JavaScript function and enabled=false.