7.3.12 Overcurrent and Short-Circuit Protection

The LM76002/LM76003 is protected from overcurrent conditions by cycle-by-cycle current limiting on both peak and valley of the inductor current. Hiccup mode is activated if a fault condition persists to prevent overheating.

High-side MOSFET overcurrent protection is implemented by the nature of the peak current-mode control. The HS switch current is sensed when the HS is turned on after a blanking time. The HS switch current is compared to the either the minimum of a fixed current set point (I_SC) or the output of the voltage regulation loop minus slope compensation every switching cycle. The slope compensation increases with duty cycle and tends to lower the HS current limit above 60% duty cycle as it lowers below I_SC. See Typical Characteristics.

When the LS switch is turned on, the current going through it is also sensed and monitored. Before turning off the LS switch at the end of every clock cycle, the LS current is compared to the LS current limit. If the LS current limit is exceeded, the LS MOSFET stays on, and the HS switch is not turned on. The LS switch is kept ON so that inductor current keeps ramping down, until the inductor current ramps below I_LSLIMIT. The LS switch is turned off once the LS current falls below the limit, and the HS switch is turned on again after a dead time.

If the current of the LS switch is higher than the LS current limit for 128 consecutive cycles, and the feedback voltage falls 60% below regulation, hiccup current-protection mode is activated. In hiccup mode, the regulator is shut down and kept off for 40 ms typically before the LM76002/LM76003 tries to start again. If overcurrent or a short-circuit fault condition still exists, hiccup repeats until the fault condition is removed. Hiccup mode reduces power dissipation under severe overcurrent conditions, and prevents overheating and potential damage to the device. Under non-severe overcurrent conditions when the feedback voltage has not fallen 60% below regulation, the LM76002/LM76003 reduces the switching frequency and keeps the inductor current valley clamped at the LS current limit level. This operation mode allows slight overcurrent operation during load transients without tripping hiccup.

If tracking was used for initial sequencing the device attempts to restart using the internal soft-start circuit until the tracking voltage is reached.