5V shunt reference in a SOT-23-3 — what it delivers
The LM4040CEM3X-5.0 is a precision shunt voltage reference from Texas Instruments that delivers a fixed 5V output with ±0.5% initial tolerance. As a shunt reference, it behaves like a Zener diode — it regulates the voltage across its terminals by shunting current through the cathode. The minimum cathode current is 83 µA, which keeps the power budget low in battery-operated designs, while the maximum output current of 15 mA can drive modest loads or bias an ADC reference input.
Tolerance and drift — the C-grade precision tier
The ±0.5% initial accuracy and 100 ppm/°C temperature coefficient place this in the middle precision tier of the LM4040 family. For a 5V output, ±0.5% means the output at 25°C can be anywhere from 4.975V to 5.025V. This noise floor is acceptable for general-purpose reference duty; for noise-sensitive analog front-ends, a larger filter capacitor or a lower-noise reference like the LM4040A would be a better fit.
Any stock in the market is new-old-stock or surplus inventory that has already left the factory. The package is Tape & Reel (TR) in a standard SOT-23-3 footprint (TO-236-3 / SC-59 / SOT-23-3).
Pin-compatible replacement path
The LM4040AIM3-5.0 is the most direct pin-compatible replacement. It shares the same SOT-23-3 footprint, fixed 5V output, and shunt topology, but upgrades the tolerance to ±0.1% and the temperature coefficient to 30 ppm/°C. The LM4040CEM3X-5.0 can be replaced by the LM4040AIM3-5.0 in any existing design without board changes — the only difference is tighter precision specs on the A-grade part. For a broader replacement search, any LM4040 variant with the same 5V fixed output in SOT-23-3 will be footprint-compatible. The tolerance and tempco grades (A, B, C, D) are the only parametric variables — the base die and pinout are identical across the family. The base product number LM4040 covers all these options.