Automotive-grade 2.5V shunt reference in SOT-23-3
The Texas Instruments LM4040QEEM3-2.5/NOPB is a precision shunt voltage reference delivering a fixed 2.5V output with ±2% initial tolerance. The shunt architecture requires only a single external resistor to set the bias current — the cathode current floor is 73 µA, and the device can sink up to 15 mA while maintaining regulation. This simplicity and the small SOT-23-3 footprint make it a direct fit for space-constrained automotive PCBs where a dedicated reference IC is preferred over a resistor divider from the supply rail.
Tempco and noise — the precision budget
The temperature coefficient is 150 ppm/°C. Wideband noise is specified at 35 µVrms over 10 Hz to 10 kHz. For a 12-bit ADC with a 2.5V reference, this noise contributes roughly 0.06 LSB rms — negligible for most automotive sensor interfaces. For 16-bit or higher resolution, the noise floor may need post-filtering or a lower-noise reference.
Package and mounting — SOT-23-3 checklist
The pinout is standard for shunt references: cathode (output), anode (ground), and no-connect or trim. For the 15 mA maximum output current at 2.5V, the internal power dissipation is 37.5 mW — well within the package capability even at 125°C ambient.
The base product number is LM4040, a long-running TI family with broad second-source coverage across the industry. The part is specified into the BOM; the procurement decision is whether the ±2% tolerance and 150 ppm/°C tempco meet the application error budget, or whether a tighter-grade sibling is needed.