SNVSBV1D February 2022 – November 2024 LMQ66410-Q1 , LMQ66420-Q1 , LMQ66430-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 the duty cycle is limited by minimum off time. After this limit is reached, as shown in Figure 7-21, and the clock frequency was to be maintained, the output voltage can fall. Instead of allowing the output voltage to drop, the device 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 after peak inductor current is achieved or after a pre-determined maximum on time, tON-MAX, of approximately 9 µs passes. As a result, after 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 7-20, 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 VDROP1. For additional information on recovery from dropout, refer to Figure 7-10.