When the EN pin of the REF20xx is pulled high, the device is in active mode. The device should be in active mode for normal operation. The REF20xx can be placed in a low-power mode by pulling the ENABLE pin low. When in shutdown mode, the output of the device becomes high impedance and the quiescent current of the device reduces to 5 µA in shutdown mode. See the Electrical Characteristics for logic high and logic low voltage levels.