SNVS783K January 2012 – August 2021 LM5017
The LM5017 device contains an intelligent current limit off-timer. If the current in the buck switch exceeds 1.02 A, the present cycle is immediately terminated, and a non-resetable off-timer is initiated. The length of the off-time is controlled by the FB voltage and the input voltage VIN. As an example, when FB = 0 V and VIN = 48 V, the off-time is set to 16 μs. This condition occurs when the output is shorted and during the initial part of start-up. This VIN dependent off-time ensures safe short circuit operation up to the maximum input voltage of 100 V.
In cases of overload where the FB voltage is above zero volts (not a short circuit) the current limit off-time is reduced. Reducing the off-time during less severe overloads reduces the amount of foldback, recovery time, and start-up time. The off-time is calculated from Equation 4.
The current limit protection feature is peak limited. The maximum average output current will be less than the peak.