The ENx pin provides electrical on and off control of the device. After the ENx pin voltage exceeds the threshold voltage, the device starts operation. If each ENx pin voltage is pulled below the threshold voltage, the regulator stops switching and enters a low quiescent-current (I_Q) state.

The ENx pin has an internal pullup current source, allowing the user to float the ENx pin to enable the device. If an application requires controlling the ENx pin, use open-drain or open-collector output logic to interface with the pin.

The device implements internal UVLO circuitry on the VIN pin. The device is disabled when the VIN pin voltage falls below the internal UVLO threshold of the input voltage. The internal UVLO threshold of the input voltage has a hysteresis of 500 mV. If an application requires either a higher UVLO threshold on the VIN pin or a secondary UVLO on the PVINx in split-rail applications, then the user can configure the ENx pin as shown in Figure 7-2, Figure 7-3, and Figure 7-4. When using the external UVLO function, TI recommends setting the hysteresis higher than 500 mV.

The ENx pin has a small pullup current, I_p, which sets the default state of the pin to enable when no external components are connected. The pullup current is also used to control the voltage hysteresis for the UVLO function because it increases by I_h after the ENx pin crosses the enable threshold. Use Equation 2 and Equation 3 to calculate the UVLO thresholds.

Equation 2.

Equation 3.

where

• I_h = 3 µA
• I_p = 3.9 µA
• V_ENRISING = 1.2 V
• V_ENFALLING = 1.15 V

Figure 7-2 Adjustable V_IN UVLO

Figure 7-4 Adjustable V_IN and PVIN UVLO

Figure 7-3 Adjustable PVIN UVLO, V_IN > 4 V