Looking at the datasheet for the MC33880:
In Table 4: Static Electrical Characteristics, the Output Fault Detect Threshold VOUTth(F) is given as 1.0V minimum to 3.0V maximum. This is the threshold for the Output OFF Open Load Fault detection which is explained on Page 17. The description is:
“An output off open load fault is indicated when the drain-to-source voltage is less than the output threshold voltage (VTHRES) of 1.0 V to 3.0 V. Hence, the 33880 will declare the load open in the OFF state when the VDS is less than 1.0 V.”
Please advise if there is any hysteresis on this threshold or any noise filtering that might stop the fault detection circuit from chattering away on a noisy signal.