We have a web application that does time-tracking, payroll, and HR. As a result, we have to write a lot of fixed-width data files for export into other systems (state tax filing
Perhaps the dbase functions are what you want to use. They are not OOP, but it probably would not be too difficult to build a class that would act on the functions provided in the dbase set.
Take a look at the link below for details on dbase functionality available in PHP. If you're just looking to create a file for import into another system, these functions should work for you. Just make sure you pay attention to the warnings. Some of the key warnings are:
http://php.net/manual/en/book.dbase.php