The VDDQ SMPS has cycle-by-cycle overcurrent limiting protection. The inductor current is monitored during the off-state using the low-side MOSFET R_DS(on) and the controller maintains the off-state while the voltage across the low-side MOSFET is larger than the overcurrent trip level. The current monitor circuit inputs are PGND and SW pins so that those should be properly connected to the source and drain terminals of low-side MOSFET. The overcurrent trip level, V_TRIP, is determined by Equation 4.

Equation 4.

where

• R_TRIP is the value of the resistor connected between the TRIP pin and GND
• I_TRIP is the current sourced from the TRIP pin. I_TRIP is 10 μA typically at room temperature, and has 4700 ppm/°C temperature coefficient to compensate the temperature dependency of the low-side MOSFET R_DS(on).

Because the comparison is done during the off-state, V_TRIP sets the valley level of the inductor current. The load current OCL level, I_OCL, can be calculated by considering the inductor ripple current as shown in Equation 5.

Equation 5.

where

• I_IND(ripple) is inductor ripple current

In an overcurrent condition, the current to the load exceeds the current to the output capacitor, thus the output voltage tends to fall down. Eventually, it crosses the undervoltage protection threshold and shuts down.