The UCC33420-Q1 has a fault reporting mechanism that can alert a system level MCU or monitoring circuitry of faulty onditions on the device that resulted in a shutdown. If an input over-voltage , over-temperature or output under voltage protection faults occur. The primary-side controller and fault monitoring system will enable a current source that will sink I_Fault current for t_Fault duration. If a resistor >18kΩ is connected between the MCU and the EN/FLT pin, the V_FLT will be pulled low for the same t_Fault duration whenever one of the abovementioned faults occur that resulted in a shutdown of the device as shown in Figure 6-2. If the fault reporting mechanism is not required on the system, the EN/FLT pin can be connected directly to the enable source voltage without the 18kΩ resistor.

The device has a auto-restart feature that occur after the device is shutdown only due to when output under-voltage or over-temperature faults occur. After the t_Fault time expires, a 160ms timer will start and the part will attemp a new soft-start sequence as shown in Figure 6-3. If the fault has been removed, the VCC will soft-start to regulation successfully. If the fault remains , the part will shutdown again and report the fault. The device can continuously operate safely in hiccup mode as long as the fault occurs.

Figure 6-2 Fault Reporting Mechanism

Figure 6-3 Auto-restart operation