The UVLO circuit verifies that the device stays disabled before the input supply reaches the minimum operational voltage range, and makes sure that the device shuts down when the input supply collapses. Figure 8-2 shows the UVLO circuit response to various input voltage events. The diagram can be separated into the following parts:

• Region A: The device does not start until the input reaches the UVLO rising threshold.
• Region B: Normal operation, regulating device.
• Region C: Brownout event above the UVLO falling threshold (UVLO rising threshold – UVLO hysteresis). The device remains enabled even if the output falls out of regulation.
• Region D: Normal operation, regulating device.
• Region E: Brownout event below the UVLO falling threshold. The device is disabled in most cases and the output falls because of the load and active discharge circuit. The device is re-enabled when the UVLO rising threshold is reached by the input voltage and a normal start-up follows.
• Region F: Normal operation followed by the input falling to the UVLO falling threshold.
• Region G: The device is disabled when the input voltage falls below the UVLO falling threshold to 0 V. The output falls because of the load and active discharge circuit.

Figure 8-2 Typical UVLO Operation