The EN pin provides electrical ON and OFF control for the LM22678 device. When VEN is below 1.6 V, the device is in shutdown mode. The current drain from the input supply, in this state, is 25 µA (typ) at an input voltage of 12 V. The EN input has an internal pullup of about 6 µA. The LM22678 also incorporates an input undervoltage lockout (UVLO) feature. This prevents the regulator from turning on when the input voltage is not great enough to properly bias the internal circuitry. The rising threshold is 4.3 V (typ.) while the falling threshold is 3.9 V (typ.).