DRV8301 Fault pin problem

Hi all

I have a custom board with a DRV8301 driving a 3-phase PMSM motor.

When I apply 50% duty-cycle pwm to the three phases, that is, motor is stoped,

fault pin goes high and low

however, when  pwm duty-cycle is not 50% ,  that is, motor is rotated,

fault pin goes high, no problem.

and  OCTW pin goes always high.

there are operation information of my custom board here:

PWM frequency : 10KHz

PVDD : 24V

GVDD : about 10V

FET : CSD18533Q5A, Qg=29nC

there are schematic and layout here:

and there is snap shot :

where :

1: GH_B

2: GL_B

3: /Fault

4: GVDD

Do you have any idea what I should try?

thanks for reading.