How to split a csv file in PHP?

I've got a large csv file that I'm creating using php.  At the end of the script, I have a single variable that contains the entire csv file contents (less the header which I have in a separate variable).  I want to run the csv file variable through a splitter that will break down the file into chunks of N lines.  I upload the files and am file size limited.  Obviously, I'd need to split the file after a /r/n so it breaks at the end of a line.  

I'd ultimately like a function that looks something like this:

$csv_array=split_csv($num_lines, $input_csv_file, $csv_header);

but if someone can get me on the right track, I'm happy to code it up and share it.