SNVS983A April 2024 – August 2024 TPS7H4011-SP
PRODMIX
Refer to the PDF data sheet for device specific package drawings
Since the voltage on the COMP pin is proportional to the device output current, by clamping the COMP voltage, another method is achieved to protect the device from overcurrent events. Specifically, if COMP rises above COMPSHDN (typically 1.9V), the part will shutdown after a small delay time, tCOMP(delay).
This feature is a complement to the HS1 and HS2 current limits. Since the slew rate of COMP is limited by the overall loop bandwidth and by the drive strength of the error amplifier, the time it takes COMP to reach COMPSHDN during a fault depends on the loop compensation and specific type of fault. During most faults, HS1 will be reached before COMP reaches COMPSHDN. HS2 will often be reached before COMP reaches COMPSHDN; however depending on the fault type, COMP may reach COMPSHDN and disable the part before HS2 is reached. Consequently, COMPSHDN can be thought of as a type of fail-safe.
After COMP reaches COMPSHDN and tCOMP(delay) passes, the device stops switching and begins discharging the SS_TR pin through a pull-down resistance, RSS(discharge) (typically 442Ω). The part will not attempt a restart until SS_TR has discharged to SSstartup (typically 20mV). This provides a cool down period for the TPS7H4011. Note that this discharge time is directly dependent upon the value of the soft start capacitor, CSS. An example of the COMP shutdown functionality is shown in the simplified waveforms of Figure 8-17.
Additionally, COMP may reach COMPSHDN if an aggressive load step is applied to the output load and a high loop bandwidth is utilized. This is because in this situation, COMP can slew higher faster than the load can respond. This can be avoided through a compensation network that is appropriately designed for the worse case load step.