Typically, data sheets of shunt references do not specify no-load current. Instead, the data sheets of shunt references often list a minimum operating current. This parameter specifies the minimum current the reference must draw to maintain regulation. Note that a shunt reference must draw at least the minimum operating current under full-load conditions. In some applications, the minimum operating current, which some data sheets call regulation current, is negligible because this current is so much smaller than the load current.
Manufacturers often specify ground current for a series reference.
Ground current measures the operating current at a given load. A series reference is in series with the load, so a measure of current flowing into the reference input yields the sum of load current and operating current. Dropout voltage , V DO , important in battery-operated equipment, applies only to the series reference. V DO is the minimum difference between input and output voltage that allows the reference to maintain its specified accuracy. Battery voltage declines as the battery discharges, and, to maximize useful life in the battery, the reference must maintain an accurate output voltage while powered by the lowest possible battery voltage.