The switched-mode regulators internal power MOSFETs gate drivers are supplied by the VREG internal linear regulator. The VREG regulator operates either in regulated LDO mode or in unregulated switch mode, depending on the availability of an external supply at the EXTSUP pin. The internal linear-regulator output at the VREG pin should be decoupled to ground using a 2.2-μF (typical) ceramic capacitor. This pin has internal current-limit protection in regulated LDO mode only and must not be used to power any other circuit.

The VREG regulator is powered from the AVIN pin by default when the EXTSUP voltage is less than 4.7 V (typical value with the V_EXTSUP voltage rising). If the VIN pin is expected to be at high voltage levels, excessive power dissipation can occur in this regulator. In this case, TI recommends powering the VREG regulator from the EXTSUP pin, which can be connected to a 5-V power-supply source. When the EXTSUP pin is connected to a power-supply source that has a sufficiently high voltage, the VREG regulator is automatically switched off and an alternative path with a linear pass switch from the EXTSUP pin to the VREG pin is turned on to improve efficiency. 5.25 V is the maximum voltage that must be applied to the EXTSUP pin. The source for the EXTSUP pin can be the BOOST output voltage.

In case of the VREG undervoltage event, the following occurs:

• All switched-mode regulators are disabled.
• The device goes into the OFF state.
• The VREG_UV bit is latched in the Analog_Latch.

In case of the VREG overvoltage event, the following occurs:

• All switched-mode regulators are disabled.
• The device goes into the OFF state.
• The VREG_OV bit is latched in the Analog_Latch.