DRV8307: The 8307 driver is assering faultn low for approx. 160 us when the PWM DC is changed from 0% to any % during initial turn on.

Part Number:DRV8307

We are using the 8307 driver to interface to a  reciprocating piston pump. To turn on the pump when we change the PWM DC from 0% to 20% or 0%to 50 % or 0% to 100% or 0% to any %, faultn is asserted low for approx. 160 us .We want to know why the fault is  asserted during pump initial turn on? The fault is never asserted once the pump is turned on and PWM DC is changed.