7.3.12 Overcurrent and Short-Circuit Protection

The LM46001 is protected from overcurrent conditions by cycle-by-cycle current limiting on both peak and valley of the inductor current. Hiccup mode is activated to prevent overheating if a fault condition persists.

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 set blanking time. The HS switch current is compared to the output of the error amplifier (EA) minus slope compensation every switching cycle. See Functional Block Diagram for more details. The peak current of the HS switch is limited by the maximum EA output voltage minus the slope compensation at every switching cycle. The slope compensation magnitude at the peak current is proportional to the duty cycle.

When the LS switch is turned on, the current going through it is also sensed and monitored. The LS switch is turned OFF at the end of a switching cycle if its current is above the LS current limit I_LS-LIMIT. The LS switch is kept ON so that inductor current keeps ramping down, until the inductor current ramps below I_LS-LIMIT. Then the LS switch is turned OFF, and the HS switch is turned on after a dead time. If the current of the LS switch is higher than the LS current limit for 32 consecutive cycles and the power-good flag is low, hiccup current protection mode is activated. In hiccup mode, the regulator is shut down and kept off for 5.5 ms typically before the LM46001 tries to start again. If over-current or short-circuit fault condition still exist, hiccup repeats until the fault condition is removed. Hiccup mode reduces power dissipation under severe over-current conditions, preventing over heating and potential damage to the device.

Hiccup is only activated when the power-good flag is low. Under non-severe overcurrent conditions when V_OUT has not fallen outside of the PGOOD tolerance band, the LM46001 reduces the switching frequency and keep the inductor current valley clamped at the LS current limit level. This operation mode allows slight over current operation during load transients without tripping hiccup. If the power-good flag becomes low, hiccup operation starts after LS current limit is tripped 32 consecutive cycles.