Generate file ".sql" from CODEIGNITER

How about, someone who can help me generate a file ".sql" a backup of my database from php using codeigniter, which are only some tables which are in an array

$ tables = array (                 "table1", "table2", "table3");

and that the file is saved in an example project folder

http://127.0.0.1/nomProyecto/index.php/assets/backups/archivo.sql