It operates as a shunt (two-terminal) reference, meaning it regulates voltage by shunting current through the device — similar to a Zener diode but with tighter accuracy and lower temperature drift. The SOT-23-3 package (TO-236-3, SC-59 alternative) is a common small-signal footprint, making this a straightforward drop-in for designs already using a 3 V shunt reference in that package.
Cathode current and noise — sizing the bias resistor
The device sinks up to 15 mA output current, with a minimum cathode current of 82 µA needed to maintain regulation. That 82 µA floor sets the minimum bias current through the external resistor from the supply rail — a common gotcha when designers assume a shunt reference draws negligible current. Wideband noise is specified at 35 µVrms over the 10 Hz to 10 kHz band. For a 3 V reference, that is about 12 ppm of the output — clean enough for a 12-bit ADC reference path, though a 16-bit system may want a lower-noise grade.
Pin-compatible alternatives in the LM4040 family
The base product number LM4040 covers a range of voltage options (2.048 V, 2.5 V, 3 V, 4.096 V, 5 V, etc.) and tolerance grades (0.1%, 0.2%, 0.5%, 1%) all in the same SOT-23-3 footprint.