When the EN pin of the REF61xx is pulled high, the device is in active mode. The device must be in active mode for normal operation.
To place the REF61xx into a shutdown mode, pull 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 1 µA (typ). See the enable pin voltage parameter in the Electrical Characteristics table for logic high and logic low voltage levels.