trying to write an array to a text file, but it is failed, can anybody say, WHY?

    $filename= 't12a';


  for ($pnum = 1; $pnum <= 15; $pnum++){
                $bbal = 3;
                $ipmnt = 14 * 5;
                $ppmnt = 26 - 7;
                $ebal = 48 - 4;
                $ccint = 54 + 45;
                $cpmnt = 25 + 54;


                $db_data_txt[] = array('pn' => $pnum, 'bb' => sprintf("%01.2f",$bbal),'ip'=>sprintf("%01.2f",$ipmnt),'pp'=>sprintf("%01.2f",$ppmnt),'eb'=>sprintf("%01.2f",$ebal),'ci'=>sprintf("%01.2f",$ccint),'cp'=>sprintf("%01.2f",$cpmnt));



  }


 $con= $db_data_txt;


if ( ! write_file("./files/{$filename}.doc", $con))
{
     echo 'Unable to write the file';
}
else
{
     echo 'File written!';
}