unable to write a text file larger than 10Mb

Hello All, This is very imp and urgent for me. I've a very large db on my remote website. I want to get a backup of that db. phpmyadmin is installed on the server..but if failed to create the backup (may b coz of the time outs). so i wrote my own class to get the backup. Its working fine except that PHP is not able to write a file larger than 10Mb. I've tried to export the data to Excel...The same problem repeated again. Is there any parameters to change in php to make it write larger files...??? /sagar