3 V shunt reference with ±0.1% tolerance — the bench-grade choice
The Texas Instruments LM4040A30IDBZRG4 is a precision shunt voltage reference delivering a fixed 3 V output with an initial tolerance of ±0.1% — tight enough to set the ADC reference in a 12-bit system without external trimming. It's the A-grade variant of the LM4040 family, which means the tolerance and temperature drift are binned tighter than the standard ±0.5% or ±1% parts.
For a 3 V reference, that works out to about 12 ppm rms, clean enough for a 16-bit SAR converter without an external filter. The temperature coefficient is 100 ppm/°C, so from 25°C to 85°C the output shifts by roughly 18 mV worst-case — a factor to budget if the board lives near a hot regulator or motor driver.
SOT-23-3 package and shunt topology — layout realities
The part comes in a standard SOT-23-3 package (also listed as TO-236-3 / SC-59), which is a three-pin footprint shared across the entire LM4040 family. Being a shunt reference, it sits in parallel with the load and requires a series resistor from the supply to set the cathode current. The datasheet cathode current range is 82 µA minimum to 15 mA maximum — stay above the minimum to guarantee regulation, and keep the total current (load + reference) under 15 mA to avoid exceeding the output current rating.