TPS54620: Overload Protect for TPS54620

Saber,

Tye TPS54620 has cycle by cycle over current limit. During the on time, the switch current is increasing. When the current reaches 11 A typical (8 A minimum) the on time is terminated and the off time begins. During the off time, the switch current is decreasing. The TPS54620 monitors the low side switch current at the end of the off time. If the current is above the low side source current limit of 10 A typical (7 A minimum), the on time is delayed and teh low side switch stays on until the switch current is below the limit, then the next switching cycle begins. The effect of this limiting action is to reduce the duty cycle below that which would normally be required for regulation, so the output voltage will fall back.

In your case, you have increased the current beyond the rating for the inductor. You have probably caused it to saturate. Proper operation of the current limit function requires that the switch current, which is the same as the inductor current have the normal ramp characteristic.