public function export_data($data = array())
{
# code...
include_once(APP_PATH.'Tools/PHPExcel/Classes/PHPExcel/Writer/IWriter.PHP') ;
include_once(APP_PATH.'Tools/PHPExcel/Classes/PHPExcel/Writer/Excel5.PHP') ;
include_once(APP_PATH.'Tools/PHPExcel/Classes/PHPExcel.PHP') ;
include_once(APP_PATH.'Tools/PHPExcel/Classes/PHPExcel/IOFactory.PHP') ;
$obj_PHPexcel = new PHPExcel();
$obj_PHPexcel->getActiveSheet()->setCellValue('a1','Key');
$obj_PHPexcel->getActiveSheet()->setCellValue('b1','Value');
if($data){
$i =2;
foreach ($data as $key => $value) {
# code...
$obj_PHPexcel->getActiveSheet()->setCellValue('a'.$i,$value);
$i++;
}
}

$obj_Writer = PHPExcel_IOFactory::createWriter($obj_PHPexcel,'Excel5');
$filename = "outexcel.xls"; header("Content-Type: application/force-download");
header("Content-Type: application/octet-stream");
header("Content-Type: application/download");
header('Content-Disposition:inline;filename="'.$filename.'"');
header("Content-Transfer-Encoding: binary");
header("Last-Modified: " . gmdate("D,d M Y H:i:s") . " GMT");
header("Cache-Control: must-revalidate,post-check=0,pre-check=0");
header("Pragma: no-cache");
$obj_Writer->save('PHP://output');
}