3 V shunt reference — what the ratings tell you
It is a precision shunt — it regulates by shunting current through the cathode to ground, so it needs a series resistor from the supply rail, not a separate input pin. The ±0.2% initial tolerance and 100 ppm/°C temperature coefficient mean this reference holds 3 V within 6 mV at 25 °C, and drifts about 0.3 mV over a 30 °C swing. That is tight enough for a 10-bit ADC reference or a comparator threshold. Cathode current is 67 µA typical — the minimum current needed to keep the shunt regulating. The device can sink up to 15 mA at the output, so the series resistor must be sized so the cathode current stays above 67 µA at minimum supply and maximum load.
Sourcing an obsolete precision reference
The LM4040BIM3-3.0 is listed as Obsolete on the lifecycle record.
SOT-23-3 (TO-236-3, SC-59) — three leads, 1.5 mm pitch, 2.9 mm body length. The footprint is standard for small-signal transistors and references; it fits a 3-pin SOT-23 land pattern. Surface-mount only.