The VIN UVLO circuit makes sure that
the regulator remains disabled when the input
supply voltage is below the minimum operational
voltage range, and makes sure that the regulator
shuts down when the input supply collapses.
Similarly, the VBIAS UVLO circuit makes
sure that the regulator remains disabled when the
bias supply voltage is less than the minimum
operational voltage range, and makes sure that the
regulator shuts down when the bias supply
collapses.
Figure 8-2 shows the UVLO circuit response to various
input or bias voltage events. The diagram can be
separated into the following parts:
- Region A: The output remains off while the input or bias voltage is below 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
possibly 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 as a
result of the load and active discharge circuit.
The device is re-enabled when the UVLO rising
threshold is reached and a normal start up
follows.
- Region F: Normal operation followed by the input or bias falling to the UVLO falling threshold
- Region G: The device is disabled when the input or bias voltages fall below the UVLO falling threshold to 0 V. The output falls as a result of the load and active discharge circuit.