The TPS544C26 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 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 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 programmable, cycle-by-cycle negative overcurrent (NOC) limit through (B4h) IOUT_NOC_LIMIT register. The available NOC thresholds which scale with ICC_MAX setting (see ICC_MAX) are shown in Table 7-10. Similar with the positive overcurrent limit, the inductor current is monitored during the low-side MOSFET ON period. To prevent too large negative current and a damage of low-side MOSFET, the device turns off the low-side MOSFET after the detected on the low-side MOSFET exceeds the selected NOC limit. And then the high-side FET is turned on for an on-time determined by PVIN, SEL_NOC_TON bit (see (ADh) COMP3) and f_SW setting).

The NOC operation usually happens after an overvoltage event but can also happen during VOUT step-down transition with fast slew rate.