SNVSB79B November 2018 – May 2020 LM25180
In case of an overcurrent condition on the isolated output(s), the output voltage drops lower than the regulation level since the maximum power delivered is limited by the peak current capability on the primary side. The peak primary current is maintained at 1.5 A (plus an amount related to the 100-ns propagation delay of the current limit comparator) until the output decreases to the secondary diode voltage drop to impact the reflected signal on the primary side. At this point, the LM25180 assumes the output cannot be recovered and re-calibrates its switching frequency to 9 kHz until the overload condition is removed. The LM25180 responds with similar behavior to an output short circuit condition.
A failsafe current limit set at 2.4 A, or 1.6 times the nominal peak current limit, provides redundant fault protection in case of transformer short circuit or saturation effects. This initiates a 7.5-ms hiccup interval after eight overcurrent events.