ZHCSJW0D June 2019 – March 2020 TPS62840
The TPS6284x integrates a current limit on the high-side as well as on the low-side MOSFETs to protect the device against overload or short circuit conditions. The current in the switches is monitored cycle-by-cycle. If the high-side MOSFET current limit (ILIMF) trips, the high-side MOSFET is turned off and the low-side MOSFET is turned on to ramp the inductor current down. Once the inductor current decreases below the low-side current limit (ILIMF), the low-side MOSFET turns off and the high-side MOSFET turns on again.
During soft start, the current limit is reduced to ILIMF_SS. After soft start has finished, the current limit value increases to the normal value ILIMF.
Due to internal propagation delay, the actual inductor current can exceed the static current limit during that time. The dynamic current limit can be calculated as follows:
In forced PWM mode, 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.