The VIN UVLO circuit makes sure that the device remains disabled before the input supply reaches the minimum operational voltage range. The VIN UVLO circuit also makes sure that the device shuts down when the input supply collapses. Similarly, the VBIAS UVLO circuit makes sure that the device stays disabled before the bias supply reaches the minimum operational voltage range. The VBIAS UVLO circuit also makes sure that the device shuts down when the bias supply collapses.
Figure 8-2 depicts 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 either 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 may fall
out of regulation but the device is still
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 either the input or bias voltage falls below the UVLO falling threshold to 0 V. The output falls as a result of the load and active discharge circuit.