Delayed shutdown upon overcurrent. A capacitor and a resistor are connected from this pin
to GND to set both the maximum duration of an overcurrent condition before the IC stops
switching and the delay after which the IC restarts switching. Every time the voltage on the
ISEN pin exceeds 0.8 V the capacitor is charged by an internal 150μA current generator and
is slowly discharged by the external resistor. If the voltage on the pin reaches 2 V, the soft
start capacitor is completely discharged so that the switching frequency is pushed to its
maximum value and the 150 μA is kept always on. As the voltage on the pin exceeds 3.5 V
the IC stops switching and the internal generator is turned OFF, so that the voltage on the
pin will decay because of the external resistor. The IC will be soft-restarted as the voltage
drops below 0.3V. In this way, under short circuit conditions, the converter will work
intermittently with very low input average power.