The switch current limit prevents the device from drawing excessive current in case of externally-caused overcurrent or short circuit condition. Due to an internal propagation delay (typically 60 ns), the actual AC peak current can exceed the static current limit during that time.
If the current limit threshold is reached, the device delivers its maximum output current. Detecting this condition for 32 switching cycles (about 13 μs), the device turns off the high-side MOSFET for about 100 μs which allows the inductor current to decrease through the low-side MOSFET's body diode and then restarts again with a soft start cycle. As long as the overload condition is present, the device hiccups that way, limiting the output power.
In forced PWM devices, a negative current limit (ILIMN) is enabled to prevent excessive current flowing backwards to the input. When the inductor current reaches ILIMN, the low-side MOSFET turns off and the high-side MOSFET turns on and kept on until TON time expires.