SLVSDV8 July 2017 TPS54424
The EN pin provides on/off control of the device. Once the EN pin voltage exceeds its threshold voltage, the device starts operation. If the EN pin voltage is pulled below the threshold voltage, the regulator stops switching and enters low operating current state. The EN pin has an internal pull-up current source, Ip, allowing the user to float the EN pin for enabling the device. If an application requires controlling the EN pin, an open drain or open collector output logic can be interfaced with the pin.
An external resistor divider can be added from VIN to the EN pin for adjustable UVLO and hysteresis as shown in Figure 27. The EN pin has a small pull-up current Ip which sets the default state of the pin to enable when no external components are connected. The pull-up current is also used to control the voltage hysteresis for the UVLO function since it increases by Ih once the EN pin crosses the enable threshold. The UVLO thresholds can be calculated using Equation 2 and Equation 3. When using the adjustable UVLO function, 500 mV or greater hysteresis is recommended. For applications with very slow input voltage slew rate, a capacitor can be placed from the EN pin to ground to filter any glitches on the input voltage.