$this->load->library('excel');
$file_name = 'Demo';
$arrHeader = array('Name', 'Mobile');
$arrRows = array(0=>array('Name'=>'Jayant','Mobile'=>54545), 1=>array('Name'=>'Jayant1', 'Mobile'=>44454), 2=>array('Name'=>'Jayant2','Mobile'=>111222), 3=>array('Name'=>'Jayant3', 'Mobile'=>99999));
$this->excel->getActiveSheet()->fromArray($arrHeader,'','A1');
$this->excel->getActiveSheet()->fromArray($arrRows);
header('Content-Type: application/vnd.ms-excel'); //mime type
header('Content-Disposition: attachment;filename="'.$file_name.'"'); //tell browser what's the file name
header('Cache-Control: max-age=0'); //no cache
$objWriter = PHPExcel_IOFactory::createWriter($this->excel, 'Excel5');
$objWriter->save('php://output');