For a buck converter, during the on-time of the high-side MOSFET, the switch current increases at a linear rate determined by the input voltage, output voltage, on-time, and output inductor value. During the on-time of the low-side MOSFET, the current decreases linearly. The average value of the switch current equals the load current.

The output overcurrent limit (OCL) in the device is implemented using a cycle-by-cycle valley current detect control circuit. The inductor current is monitored during the on-time of the low-side MOSFET by measuring the low-side MOSFET drain-to-source current. If the measured drain-to-source current of the low-side MOSFET is above the current limit threshold, the low-side MOSFET stays ON until the current level becomes lower than the current limit threshold. This type of behavior reduces the average output current sourced by the device.

During an overcurrent condition, the current to the load exceeds the current to the output capacitors. Thus, the output voltage tends to decrease. Eventually, when the output voltage falls below the undervoltage-protection threshold (80%), the UVP comparator detects the fall and shuts down the device after a wait time of 70 µs. Depending on the fault recovery configuration, the device either hiccups or latches off, as described in Overvoltage and Undervoltage Protection.

Please see Section 7.3.3 for more information on setting the currently limit protection threshold.