JAJSNY9B September 2022 – February 2023 TPSM365R3 , TPSM365R6
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 the minimum off-time. After this limit is reached as shown in Figure 9-18 if clock frequency was to be maintained, the output voltage can fall. Instead of allowing the output voltage to drop, the TPSM365Rx 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 9-17 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 back to Section 9.3.12.1.