Why is the output of an LDO disabled when its input voltage decreases?

One of the possible causes of this is the tripping of undervoltage lockout (UVLO*). When the input voltage of an LDO drops to the predefined threshold, UVLO disables the LDO to prevent false operation. The LDO is re-enabled when the input voltage rises above the recovery threshold. ULVO has a hysteresis.

 

* UVLO: Under Voltage Lock Out

Figure 1 Operation of undervoltage lockout (UVLO)
Figure 1 Operation of undervoltage lockout (UVLO)

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