DRV8353RH-EVM: nFAULT have 20us pull low, which protection is it?

Tool/software:

Hi TI,

I use DRV8353RH-EVM to drive motor and I only modify MODE on EVM (connect MODE to GND and set 6x PWM mode).

When I drive motor with heavy loading, I find a 20us pull low signal on nFAULT pin every 3~10 second.

I won't find this condition on light loading.

I can't find any protection which will pull low for 20us in datasheet.

Please refer to the waveform below.

C1: DC Bus, C2: nFAULT, C4: motor phase current