The internal LDO has a lower EN threshold than the
output of the regulator. The internal LDO regulates the VCC voltage at 3.3 V,
typically when:
- The EN pin voltage is above 1.1 V (maximum) and
- The EN pin voltage is below the precision enable threshold for the output
voltage.
The precision enable circuitry is ON once VCC is above its UVLO. The internal
power MOSFETs of the SW node remain off unless the voltage on the EN terminal goes
above its precision enable threshold. The
LM6x4xx
also employs UVLO protection. If the VCC voltage is below its UVLO level, the output
of the regulator is turned off.