In constant peak current (CPC) mode, the zero crossing detect (ZCD) on the BSW pin is critical to trigger the switching instant of the next cycle, so the missing ZCD timeout feature can avoid the risk of inability to sense ZCD in a given switching cycle. The normal peak current threshold is approx. 0.33 A for every BSW switching cycle. In DCM operation of the CPC mode, the ZCD detection is enabled to allow the boost inductor current to decay to zero before the next switching cycle. The internal detection network compares the V_BSW and V_BIN to qualify for a valid ZCD event. If the ZCD event can not be detected for a given cycle, a 700-µs timer is enabled and then the next switching cycle occurs after the 700-µs has expired.

Figure 8-36 Operation Principle of Over Current Protection in Boost Mode

In constant off time (COT) mode, it is critical to prevent the inductor from reaching the saturation limit. Due to the CCM operation of COT mode, if the peak current is higher than 0.33 A after the 190-ns leading edge blank time, a 4.35-µs timer is enabled and then the next switching cycle cannot be initiated until after the 4.35 µs has elapsed. The operating principle is shown in Figure 8-36. This built-in over current protection prevents the chance of accumulated peak current overshoot in CCM, so the risk of boost inductor saturation can be eliminated.