The Texas Instruments LM4040BIM3-8.2/NOPB is a precision shunt voltage reference that delivers a fixed 8.192 V output with ±0.2% initial tolerance. As a shunt (two-terminal) reference, it behaves like a Zener diode — it regulates by shunting current through an external resistor to ground, making it simple to bias from any supply voltage above 8.192 V.
Why the ±0.2% tolerance and 100 ppm/°C drift matter
The ±0.2% initial accuracy means the output sits between 8.176 V and 8.208 V at 25°C — tight enough for 12-bit ADC references without external trim. For designs that need better than 0.5% total accuracy over temperature, this grade is a solid fit without jumping to the A-grade (±0.1%) bin.
Biasing it right — the external resistor is not optional
A shunt reference always needs an external resistor from the supply to the cathode pin to set the bias current. The LM4040BIM3-8.2/NOPB sinks a minimum of 95 µA cathode current and can deliver up to 15 mA to the load. The resistor value is chosen so that the sum of the load current and the cathode current stays between 95 µA and 15 mA over all supply and load conditions — pick it too large and the reference drops out of regulation; too small and the power dissipation in the resistor or the part exceeds ratings. For a typical 12 V rail and a 1 mA load, a 3.3 kΩ resistor works cleanly.