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The LT4356 also features an accurate current limiting circuit that protects against short circuits or excessive load current. During an overcurrent event, an active current limiting loop regulates the voltage measured across an external resistor (RSENSE) to 50mV while at the same time charging the timer capacitor. The fault timer charging current is five times larger for overcurrent faults, since more power is dissipated in the pass transistor during this condition. After timeout, the pass transistor turns off and remains off until the overcurrent condition has passed and a cool down period has elapsed. During overcurrent conditions, the MOSFET stress increases as the drain-source voltage increases. The LT4356 monitors the voltage across the external MOSFET and shortens the timer interval in proportion to the increasing drain-source voltage. This way a minor overload may persist for a longer time interval than a highly stressful short circuit condition, ensuring the MOSFET operates within its safe operating area under all conditions. While MOSFET protection is important, the real benefit of current limiting is the protection of the upstream fuse which otherwise would open and would need to be replaced.
