8.3.5.2 Bootstrap Voltage (CB)

The LMR16006 device has an integrated bootstrap regulator, and requires a small ceramic capacitor between the CB and SW pins to provide the gate drive voltage for the high-side MOSFET. The CB capacitor is refreshed when the high-side MOSFET is off and the low-side diode conducts. To improve dropout, the LMR16006 device is designed to operate at 100% duty cycle as long as the CB to SW pin voltage is greater than 3 V. When the voltage from the CB to SW pin drops to less than 3 V, the high-side MOSFET turns off using a UVLO circuit which lets the low-side diode conduct and refresh the charge on the CB capacitor. Because the supply current sourced from the CB capacitor is low, the high-side MOSFET can stay on for more switching cycles than are required to refresh the capacitor. Therefore, the effective duty cycle of the switching regulator is high. Attention must be given in maximum duty-cycle applications with a light load. To make sure the SW pin can be pulled to ground to refresh the CB capacitor, an internal circuit charges the CB capacitor when the load is light or the device is working in dropout condition.