7.3.7 Enable and Adjusting Undervoltage Lockout

The EN pin provides electrical on and off control of the device. Once the EN pin voltage exceeds the threshold voltage, the device starts operation. If the EN pin voltage is pulled below the threshold voltage, the regulator stops switching and enters low Iq state. If an application requires controlling the EN pin, use open drain or open collector output logic to interface with the pin.

For input undervoltage lockout (UVLO), use the EN pin as shown in Figure 22 to set up the UVLO by using the two external resistors. Once the EN pin voltage exceeds 1.3 V, an additional 2.8 µA of hysteresis is added. This additional current facilitates input voltage hysteresis. Use Equation 2 to set the external hysteresis for the input voltage. Use Equation 3 to set the input startup voltage. TI recommends that the minimum input shutdown voltage be set at 2.45 V or higher to ensure proper operation before shutdown.

Figure 22. Set Up Input Undervoltage Lockout.

Equation 2.

Equation 3.

where

• R₁ and R₂ are in Ω
• I_h = 2.8 µA
• I_p = 0.7 µA
• V_{EN_RISING} = 1.3 V
• V_{EN_FALLING} = 1.18 V