Dropout operation is defined as any input-to-output voltage ratio that requires frequency to drop to achieve the required duty cycle. At a given clock frequency, duty cycle is limited by minimum off time. Once this limit is reached as shown in Figure 8-21 if clock frequency was to be maintained, the output voltage would fall. Instead of allowing the output voltage to drop, the LMR436x0-Q1 extends the high-side switch on time past the end of the clock cycle until the needed peak inductor current is achieved. The clock is allowed to start a new cycle once peak inductor current is achieved or once a pre-determined maximum on time, tON-MAX, of approximately 9 µs passes. As a result, once the needed duty cycle cannot be achieved at the selected clock frequency due to the existence of a minimum off time, frequency drops to maintain regulation. As shown in Figure 8-20, if input voltage is low enough so that output voltage cannot be regulated even with an on time of tON-MAX, output voltage drops to slightly below the input voltage by VDROP. For additional information on recovery from dropout, refer to Figure 8-11.