SLVS839F July 2008 – October 2014 TPS54331
The EN pin has an internal pullup current-source that provides the default condition of the device while operating when the EN pin floats.
The TPS54331 device is disabled when the VIN pin voltage falls below the internal VIN UVLO threshold. Using an external VIN UVLO to add hysteresis is recommended unless the VIN voltage is greater than (VOUT + 2 V). To adjust the VIN UVLO with hysteresis, use the external circuitry connected to the EN pin as shown in Figure 9. When the EN pin voltage exceeds 1.25 V, an additional 3 μA of hysteresis is added. Use Equation 1 and Equation 2 to calculate the resistor values required for the desired VIN UVLO threshold voltages. The VSTOP threshold should always be greater than 3.5 V.