The TPS548C26 device is a synchronous buck converter, thus the current can flow from the device to the load or from the load into the device through SW node. When the current is flowing from the device SW node to the load the device is said to be sourcing current and the output current declared to be positive. When the current is flowing into the device SW node from the load, the device is said to be sinking current and the current is declared to be negative.

The device offers a fixed, cycle-by-cycle negative overcurrent (NOC) limit which is set to −16 A. Similar with the positive overcurrent limit, the inductor current is monitored during the low-side FET on period. To prevent too large negative current and a damage of low-side FET, the device turns off the low-side FET after the detected negative current through the low-side FET exceeds the NOC limit. And then the high-side FET is turned on for an on-time determined by PVIN, VOUT, and f_SW setting. After the high-side FET on-time expires, the low-side FET turns on again.

The device is unlikely to trigger the −16-A negative current limit during the nominal operation unless too small inductor value is chosen or the inductor becomes saturated. This NOC operation feature is used to discharge output capacitors during an overvoltage event.