3.0 V shunt reference — precision floor for the analog rail
The Texas Instruments LM4040BIM3X-3.0 is a precision shunt voltage reference delivering a fixed 3.0 V output with ±0.2% initial tolerance — tight enough to set the reference for a 12-bit ADC without external trimming. It is built around the shunt (two-terminal) topology, so it behaves like a Zener diode: you bias it through a series resistor from a higher supply rail, and it sinks whatever current is needed to hold the output at 3.0 V. This part is from the LM4040 family, a widely-used series of low-power, precision references in the SOT-23-3 footprint. The shunt architecture means it can be configured for either positive or negative output voltages relative to a floating reference point — useful in split-supply or level-shifting circuits.
The ±0.2% tolerance at 25 °C sets the absolute accuracy floor. For a 3.0 V reference, that is ±6 mV — adequate for 8- and 10-bit ADCs, and marginal for 12-bit systems that need better than 1 LSB at 3.3 V full-scale. Output current is rated at 15 mA maximum. The minimum cathode current is 67 µA, which sets the floor for the bias resistor calculation. For 16-bit or higher resolution, a bypass capacitor at the output pin (typically 0.1 µF to 1 µF) will knock down the wideband noise floor further.
Obsolete — sourcing path through independent distribution
This part is now available exclusively through the independent distribution channel — new-old-stock and surplus inventory that has already been manufactured. A design review is recommended before substituting.