Circuitry for the DRV8840 Motor Driver
As there is no sense resistor connected between the ISEN pins and ground there will be no current chopping at a set value.  Depending on the characteristics of the DC motor you are driving, enabling the device could ramp current above the internal current limit and thereby cause the open-collector fault line to be enabled.

As you have tied the fault line to 5V this could pull down this rail and possibly disable the device by cycling nSLEEP, nRESET, etc.