DRV8884: problems with the driver

Hi 

i have problems with the DRV8884, i set the enable signal to high, and the sleep signal to high , but the signal nFault is changing over the time ,  i am not sending steps, and the direction signal is high always

my VM voltage  is 12V (never change )

my VCP voltage is 16.8V 

for my first test i dont connect the motor ( my motor is 12V @ 125 ma  )

what could be the problem? 

thanks in advance 

Víctor