SNVSB70F May 2019 – June 2021 LM61460-Q1
PRODUCTION DATA
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, if clock frequency were maintained, output voltage would fall. Instead of allowing the output voltage to drop, the LM61460-Q1 extends on-time past the end of the clock cycle until 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. 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, VDROP1. For additional information on recovery from dropout, reference Figure 9-9.