Want some help about L297 chip

Hello users
I am using L297 in my project for first time,therefore i
want some help.I want to set it's chopping frequency to 20Khz so
which values should be used for resistor and capacitor?
I see its formula but i can't solves it :( .
another thing is i use four IRF540 mosfets with L297 and i set L297
chopper mode to phase type not (INH)type so did it works with 8AMP
stepper motor? also i don't uses INH1 INH2 outputs but i use sense
inputs.
please reply me soon and give me some help.

bye all :)

SALMAN HAMEED.