The V_IN 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 V_BIAS 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.

Figure 8-2 Typical V_IN or V_BIAS UVLO Circuit Operation