The REF33xx family of voltage references features extremely low dropout voltage, except for the REF3312. The REF3312 has a minimum supply requirement of 1.7 V. These references can be operated with a supply 110 mV above the output voltage with a 5-mA load (typical). For loaded conditions, a typical dropout voltage versus load graph is illustrated in Figure 4 of the Typical Characteristics.
If the supply voltage connected to the IN pin is rapidly moved when the REF33xx is connected to a capacitive load, a reverse voltage can discharge through the OUT pin and into the REF33xx. This voltage does not damage the REF33xx, provided that the voltage is less than or equal to 5 V.