Are you referring to the line frequency or pwm frequency?The IC is optimized for typical line frequency of 50 Hz and 60 Hz and was not evaluated to work at 400 Hz line. I did a quick bench verification and while there is a slight increase in output current regulation, the PF is severely degraded.

I was referring to a line frequency of 400Hz. I assume you checked an existing circuit that was already optimized for 60Hz operation and applied 400Hz. Is it possible to modify it to work at 400Hz so the PF is greater than 0.9? 

If you have an existing board, you may try to reduce the input capacitor and see if it improves. But then, there are other things you need to check like EMI and output regulation.

I don't have anything on a board at this point. I'm just trying to determine if this IC will work for my application, but it's looking like it will not. There's just not enough information for me to determine if it will, so I will need to look elsewhere.