The REF34xx references can be switched to a low power shut-down mode when a voltage of 0.5 V or lower is input to the EN pin. Likewise, the reference becomes operational for EN voltages of 1.6 V or higher. During shutdown, the supply current drops to less than 2 μA, useful in applications that are sensitive to power consumption.
If using the shutdown feature, ensure that the EN pin voltage does not fall between 0.5 V and 1.6 V because this causes a large increase in the supply current of the device and may keep the reference from starting up correctly. If not using the shutdown feature, however, the EN pin can simply be tied to the IN pin, and the reference remains operational continuously.