output_csv.php

public function exportCsvAction()
    {
        $data = [];
        $filename = "export_filename_" . date("Y_m_d_His") . ".csv";
        $response = $this->render('BBITAdminBundle:Csv:entity.csv.twig', array('data' => $data));

        $response->setStatusCode(200);
        $response->headers->set('Content-Type', 'text/csv');
        $response->headers->set('Content-Description', 'Filename description');
        $response->headers->set('Content-Disposition', 'attachment; filename=' . $filename);
        $response->headers->set('Content-Transfer-Encoding', 'binary');
        $response->headers->set('Pragma', 'no-cache');
        $response->headers->set('Expires', '0');

        $response->sendHeaders();

        return $response;
    }