This article explains the exact behavior of the fault output under unexpected (no fault) conditions
1. Condition 1
When device doesn't receive DIM for a while, this device is designed to go into low DIM mode which disables the internal LDO for the device to save energy.
When the device is off by not having DIM signal for a while (~few tens of ms), you will see FLTB flags.
2. Condition 2
When device is not enabled, FLTB always flags.
Reason :
When internal LDO is off, FLTB is designed to flag. Thus whenever EN goes low or by entering low DIM mode, you will see FLTB flags.