The UVLO circuit makes sure 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 7-2 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 output can fall out of regulation
but the device remains enabled.
- 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.