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LM4040: LM4040BIM3-2.5 accuracy

Martin Krzyzan
Prodigy 30 points
Part Number: LM4040

Dear Sirs,

over a long time we design in your LM4040 shunt references.

For one application (ADC reference) we use your LM4040BIM3-2.5. The Load is a ADC refence input. VCC is approx 5,3V. The Rv is 2400 Ohms. parallel to the LM4040 we have a 1 µF capacitor.

In the last time we can observe an output voltage above the nominal tolerance. For the BIM the nominal tolerance is 0,2%. So we can measure by many of our LM4040 output voltage between 2,506 Vto 2,507 V.

This is over the naminal tolerance from 0,2%!

We measure with a calibrated Keithley 2016THD. Room temperature is between 22 - 25 °C.

Various new combination with other RV for Diode operrating current from 100 µA to 15 mA do not change this unaccuracy extremly.

What is the reason for this voltage divergence in the last time?

Thank you and best regards

Martin

  • 0
    TI__Expert 3835 points

    Hi Martin,

    Have you tried removing the capacitor or different capacitor values? How many devices have you found to be out of tolerance? Have you tried using different voltage meters to make sure? Can you try testing the device under no load conditions (cathode floating not connecting to ADC)?

    Thanks,
    Ethan

  • 0
    TI__Mastermind 19580 points
    Hi Martin,

    Where these devices measured pre or post solder?
    Every voltage reference device experiences a solder shift and this is an additional error to the initial accuracy. The best estimate of what the solder shift would be for this device is to look at the thermal hysteresis.

    -<Marcoo
  • 0 in reply to Ethan T
    Prodigy 30 points
    Dear Ethan, also Dear Marcoo,

    thank you for your help. In the meantime I read with interest the issue "LM4040: Precision issue" from Olivier Frenette5.
    In fact, this boards with the unaccuracy LM4040 devices are manual solder with a smal Reflow-Rework unit.
    Yesterday I have measure some samples from the LM4040BIM3-2.5 only with probes in a testcircuit.
    All this samples are within the Tolerance from 0,2 %! So we think this unaccuracy in an effect from the thermal hysteresis by different solder technics.

    Thank you and best regards

    Martin