Fixed 2.5 V shunt reference for harsh environments
The Texas Instruments LM4040C25MDBZTEP is a precision shunt voltage reference that delivers a fixed 2.5 V output with ±0.64% initial tolerance. As a shunt (two-terminal) reference, it behaves like a Zener diode — it requires an external series resistor to set the bias current, which must be chosen to keep the cathode current above the 82 µA minimum and below the 15 mA maximum output capability across all load and temperature conditions.
The ±0.64% tolerance is a mid-grade precision tier within the LM4040 family. It means the output voltage at 25°C can vary from 2.484 V to 2.516 V. For a 12-bit ADC with a 2.5 V reference, this contributes roughly ±2.6 LSBs of gain error before any temperature drift is factored in. If your system budget requires tighter than 0.5% initial accuracy, step up to the LM4040A or LM4040B grade variants. The 100 ppm/°C temperature coefficient adds another ±0.01% per degree of temperature change. For precision analog chains that hold calibration across temperature, consider a series reference with a lower tempo (e.g., 20 ppm/°C) if the budget allows. This is clean enough for most 12-bit to 14-bit ADC references; for 16-bit or higher resolution, you may need to add an external RC filter or select a lower-noise reference.
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