The FAULT pin provides the user with flexibility to implement additional protections for the converter, such as input overcurrent protection or overvoltage protection, if desired. This pin can also be utilized in the event that the user desires more stringent protections than what is offered by the controller (i.e. thermal shutdown). The user can design external logic circuitry to generate the signal necessary to drive this pin based on the protection function. If the voltage on the FAULT pin exceeds 0.6 V (typical) for a duration specified by the FAULT minimum pulse width, a fault shutdown will occur. This FAULT minimum pulse width duration, which is between 0.4 µs and 1.4 µs, is intended to prevent any spurious triggering due to short-term transients. Since any short-term transient event detected on this pin that is less than 1.4 µs in duration may not activate the FAULT pin, these events should be properly evaluated by the user in order to determine the impact to the overall system. Once the fault is detected, the SS pin is discharged and the controller outputs stop switching and stay low as long as the rising threshold is exceeded on the pin. Once the fault has subsided and the voltage of FAULT falls below the falling threshold of 0.5 V (typical), the TPS7H500x-SEP enters a delay period that is dependent on the switching frequency. This delay is appoximately equal to 15 switching frequency cycles in addition to an internal logic delay. The soft-start sequence is again initiated after the delay period has finished. Equation 15 can be used to determine the length of the fault delay.

In this equation:

• t_dFLT is the fault delay duration in μs
• f_sw is the switching frequency in kHz

If the FAULT threshold is exceeded during the delay, the entire sequence is started again. Figure 8-16 shows the switching waveforms when the fault mode has been activated in the controller. Note that OUTB waveforms are only applicable for TPS7H5005-SEP and TPS7H5008-SEP.

Figure 8-16 Switching Waveforms During Fault Mode