3 V shunt reference with ±0.1% initial accuracy
It operates as a two-terminal shunt device, meaning it behaves like a Zener diode but with much tighter regulation and lower temperature drift — 100 ppm/°C typical. The 35 µVrms noise over 10 Hz to 10 kHz keeps the reference clean enough for 12-bit ADC and DAC rails in industrial control, test equipment, and battery-monitoring circuits.
15 mA cathode current — sizing the bias resistor
The LM4040A30IDBZT can sink up to 15 mA through the cathode, which sets the load-driving limit. For a 3 V rail supplying a 1 mA load from a 5 V supply, the bias resistor needs to drop 2 V at the total current (load plus minimum cathode current of 82 µA). That works out to roughly 1.8 kΩ. Push the load beyond 15 mA and the reference drops out of regulation — the output voltage starts tracking the supply. For higher current needs, step up to the LM4040B or a series reference like the REF3033.
SOT-23-3 — footprint and reflow considerations
The LM4040A30IDBZT comes in a standard SOT-23-3 package (also listed as TO-236-3 or SC-59). It is a three-lead surface-mount device with a 0.95 mm pitch. The package is MSL 1 by default — no bake required before reflow as long as the moisture barrier bag is intact. The small body means the part self-centers well during reflow, but the limited copper area on the PCB pad restricts heat sinking. For a 15 mA load at 85°C ambient, the junction temperature stays within limits, but verify the thermal budget if the part is running near max current in a hot enclosure.
ROHS3 compliant, so it ships into EU and North American markets without restriction. The base product number LM4040 covers a family of fixed-voltage shunt references from 1.225 V to 10 V, all sharing the same SOT-23-3 footprint — useful if a different voltage is needed later without a board spin.