A voltage reference is an accurate, temperature-compensated voltage source that provides specific output voltage values, such as 1.225 V, 4.096 V, or 10.000 V. Voltage reference ICs can be either shunt (two terminals) or series (three terminals). A shunt reference IC employs an external series resistor that sets the maximum current supplied to the load. Shunt references are preferable when the load is nearly constant and power-supply variations are minimal. A series reference IC generally consists of a voltage reference—typically a temperature-compensated band-gap or buried zener—and an amplifier that controls the output voltage. Series reference ICs should be considered when load current is variable and there are tight tolerances on the output voltage for temperature changes.