SLVSDV8 July 2017 TPS54424
While the low-side MOSFET is turned on the current through it is monitored. During normal operation the low-side MOSFET sources current to the load. At the end of every clock cycle, the low-side MOSFET sourcing current is compared to the internally set low-side sourcing current limit. If the low-side sourcing current is exceeded the high-side MOSFET is not turned on and the low-side MOSFET stays on for the next cycle. The high-side MOSFET is turned on again when the low-side current is below the low-side sourcing current limit at the start of a cycle. The low-side sourcing current limit prevents current runaway.
The low-side MOSFET may also sink current from the load. If the low-side sinking current limit is exceeded the low-side MOSFET is turned off immediately for the rest of that clock cycle. In this scenario both MOSFETs are off until the start of the next cycle. If the low-side MOSFET turns off due to sinking current limit protection, the low-side MOSFET can only turn on again after the high-side MOSFET turns on then off or if the device enters BOOT UVLO.