DRV8899-Q1: Mosfet PWM switching frequency

Tool/software:

Hi,

Could you please let us know the below queries
1) Whether the Mosfet PWM switching frequency : 30kHz is fixed? 
2) If it is not fixed, how to calculate the PWM frequency which is required to calculate the power dissipation of IC
3) Any internal dependency between Step frequency & Mosfet PWM frequency?

Regards
Soumya