The LM4040CEM3X-2.5 is a precision shunt voltage reference from Texas Instruments, delivering a fixed 2.5 V output with ±0.5% initial tolerance. It is designed for low-power analog circuits — ADC references, comparator thresholds, and regulator feedback dividers — where a stable, low-noise rail is needed without a series regulator. The 35 µVrms noise spec (10 Hz–10 kHz) is the headline differentiator for precision work: a 14-bit ADC with a 2.5 V reference sees about 1 LSB of noise contribution from this part alone, which is acceptable for most industrial data-acquisition chains. Cathode current is 68 µA typical, so the total supply draw through the bias resistor is under 100 µA.
Housed in a SOT-23-3 package (TO-236-3 / SC-59 compatible), it is a drop-in for any three-pin shunt reference footprint. The 100 ppm/°C drift over temperature means the output shifts across the full range.
For new designs, the LM4040 family still offers active grades (e.g., LM4040DIM3X-2.5) with the same pinout and 2.5 V output, though tolerance and temperature coefficient differ — verify the grade before substituting.