To further protect the converter during prolonged current limit conditions, the LM51551 device option provides a hiccup mode overload protection. The internal hiccup mode fault timer of the LM51551 counts the PWM clock cycles when the cycle-by-cycle current limiting occurs. When the hiccup mode fault timer detects 64 cycles of current limiting, an internal hiccup mode off timer forces the device to stop switching and pulls down SS. Then, the device will restart after 32 768 cycles of hiccup mode off-time. The 64 cycle hiccup mode fault timer is reset if eight consecutive switching cycles occur without exceeding the current limit threshold. The soft-start time must be long enough not to trigger the hiccup mode protection during soft-start time because the hiccup mode fault timer is enabled during the soft start.
To avoid an unexpected hiccup mode operation during a harsh load transient condition, it is recommended to have more margin when programming the peak-current limit.