Electronics > Metrology

Stability of 5V references compared to AD586LQ

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Andreas:
Hello,

I widely use battery powered ADCs (LTC2400 based) with AD586LQ (temperature compensated) as work horses for my measurements.
The reason why I rely on them can be seen in the attached diagram: ADC13, ADC15, ADC16 are built with AD586LQ.
ADC17 is based on LT1236AILS8-5 which is typically about a factor of 2 less stable.
And even the LM399 based 6.5 digit DMMs (the K2000 with additional temperature compensation) are not so stable when reading my most stable 7V reference LTZ#4.

Since the AD586LQ is now near unobtanium (in small quantities) I am looking for a replacement.
Of course a heated reference could do the job but I want to operate the systems battery based so power consumption of the whole cirquit should stay below 5 mA.

with best regards

Andreas



Andreas:
Hello,

first try is with AD586MNZ (the same reference in DIP8 plastic package)


I built ADC29 + ADC30 with AD586MNZ for testing.
Note: I am measuring the LTZ#4 at the input of the LTC2400.
The 5V reference is at the reference input.
So if the reference drifts to positive values the readings of the LTZ#4 on the input of the ADC go down.

Since the reference is still not pre-aged much I measured the average ageing of the references
ADC29:  +0.517 ppm/kHr
ADC30:  +0.366 ppm/kHr

Unfortunately the plastic package of the reference suffers from humidity sensitivity
(only the GND pin is soldered to the PCB the others are connected with thin wires so the PCB has no influence)

ADC29: +0.41 ppm / %rH with a time constant of ~2.61 days
ADC30: +0.42 ppm / %rH with a time constant of ~2.13 days

The diagrams show the readings from day 0 of measuremen in red.
The "prediction values" based on ageing and %rH in green.
And the filtered %rH values which are measured all 15 minutes and PT1-filtered by a time constant of 2 days or 3 days in blue.

As next candidate I want to evaluate a REF7050 in LS8-package. (still waiting for the PCBs)

with best regards

Andreas

deepfryed:
MAX6350 seems better on paper at least, though only available in the plastic DIP packages. Also the DIP versions are EOL, but still available from Digikey.

The Soulman:

--- Quote from: Andreas on January 03, 2024, 07:19:58 pm ---ADC17 is based on LT1236AILS8-5 which is typically about a factor of 2 less stable.

--- End quote ---

I would expect those to be better than that, also after the first month of use? Do you see correlation with temperature or humidity?

zepto:
What about LT1027? Advantest used it in their AD7461A which allowed for integration periods up to 10 seconds.

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