[FAQ] TPS2595: How eFuse internal FET operation in SOA is ensured?

                                                                  Built-in Thermal Protection circuit in eFuse ensures FET operation within SOA

Please refer this application note for detailed understanding.  Following is a top level summary.

• The internal FET of the eFuse devices are stressed under conditions like startup into capacitive load, limiting overcurrent, startup into output short circuit. It is important that the internal FET is not stressed beyond the SOA limits of the FET during stressful conditions so as to avoid any damage to the FET
  
  
• Over-temperature Protection (TSD) scheme is implemented in TI’s eFuse to ensure the FET is not stressed beyond its SOA limits. During stressful events there would power loss across the FET which increases the junction temperature of the eFuse. The eFuse is turned OFF when the junction exceeds the thermal shutdown threshold to protect the FET. For example, the Thermal Shutdown threshold for TPS2595 is at 157ᵒC.

• Figure below , shows Over-temperature Protection scheme turn OFF the IC to protect the FET in ‘Wake Up With Output Short to GND’ condition.

                       Wake Up With Output Short to GND

• For the same power dissipation, higher ambient temperature turns OFF the FET faster . As shown in below figure, for 10W power time to shutdown t2 at 85C is lower as compared to t1 at 25C.

                             Thermal Shutdown Time vs Power Dissipation

• To verify the robustness of our thermal protection scheme during startup in the worst case condition, wake up into short test is performed a million time.

• All our eFuse devices are designed to protect the internal FET under fault conditions as long as the device is operated within its recommended operating conditions. The robustness of the eFuse devices under conditions like overload that can stress FET is also tested during the UL 2367 evaluation process. Refer this link for more info on eFuse safety certification: www.ti.com/.../slvaeo5.pdf