To further protect the converter during prolonged current limit conditions, the LM51561 device option provides a hiccup mode overload protection. The internal hiccup mode fault timer of the device counts the PWM clock cycles when the cycle-by-cycle current limiting occurs after soft start is finished. 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 after the soft start is finished.

Figure 9-21 Hiccup Mode Overload Protection

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.