Any time the output voltage falls more than a few percent, output voltage ramps up slowly. This condition, called graceful recovery from dropout in this document, differs from soft start in two important ways:

• The reference voltage is set to approximately 1% above what is needed to achieve the existing output voltage.
• If the device is set to FPWM, it continues to operate in that mode during its recovery from dropout. If output voltage were to suddenly be pulled up by an external supply, the LMQ664x0 can pull down on the output. Note that all protections that are present during normal operation are in place, preventing any catastrophic failure if output is shorted to a high voltage or ground.

Figure 8-8 Recovery from Dropout

Figure 8-9 Typical Output Recovery from
Dropout from 8 V to 4 V

Whether output voltage falls due to high load or low input voltage, after the condition that causes output to fall below its set point is removed, the output climbs at the same speed as during start-up. Figure 8-9 shows an example of this behavior.