Inserting text in TinyMCE Editor where the cursor is

I've been trying to insert text into the TinyMCE Editor at the focused paragraph element (<p>) exactly where the cursor is but got no luck!!

var elem = tinyMCE.activeEditor.dom.get('tinymce');
var child = elem.firstChild;
while (child) {
    if (child.focused) {
        $(child).insertAtCaret("some text");
    }
    child = child.nextSibling;
}

If anyone has any idea on how to solve this I'll be very thankful.