Stability of 5V references compared to AD586LQ

[Andreas]

I recommend you take a few (3..6) REF7050 and compare them first for the one that best suits your needs (drift, ageing, etc.) before choosing one for your final PCB.
All REF70xx are good, but some variation exists in the batch you'll get.

Hello,

Unfortunately I have no socket for the LS8 package (a DIP8 package eases selection).
I have planned to populate 4 PCBs (depending on the first 2 measurements).
Do you have numbers for hysteresis over temperature and initial drift (how long).

Mind the plastic gear inside (afaik) changes its shape with temperature/aging..

In my AD587LW-Design I also use these trimmers. But with a rather high resistor (> 1 Meg) at the wiper narrowing the adjustment range to some ppm.
Additionally some trim resistors as pull up / pull down for adjusting the range directly at the adjustment input.
The original BOURNS trimmers are somewhat better than some no name trimmers with the same shape.
https://www.eevblog.com/forum/metrology/ad587lw-10v-precision-travel-standard/msg1449488/#msg1449488

with best regards

Andreas

[Conrad Hoffman]

I avoid no-name trimmers but always pad trimmers such that they cover such a small range that even gross performance problems can't affect much.

[iMo]

I recommend you take a few (3..6) REF7050 and compare them first for the one that best suits your needs (drift, ageing, etc.) before choosing one for your final PCB.
All REF70xx are good, but some variation exists in the batch you'll get.

Hello,

Unfortunately I have no socket for the LS8 package (a DIP8 package eases selection).
I have planned to populate 4 PCBs (depending on the first 2 measurements).
Do you have numbers for hysteresis over temperature and initial drift (how long).

FYI - below the aging of the REF70xx from the DS rev 09/2023  ..

[3roomlab]

how about the MAX6126 ?
their app note looks impressive



https://www.allaboutcircuits.com/technical-articles/electronic-component-aging-prediction-the-long-term-drift-in-voltage-references/

https://pdfserv.maximintegrated.com/en/an/AN7009.pdf

[Andreas]

Hello,

first result from ADC#32 with REF7050 in dead bug mounting.

Temperature cycling from 10 deg C to 40 deg C with 0.12 K/minute
one temperature cycle is nearly 12 hours.

The T.C. is fairly low but the large temperature hysteresis of 7-8 ppm @25 deg and the large ageing drift of ~4ppm/day makes the REF7050 useless for precision work.
At maximum they can be used for ratiometric (RTD temperature) measurements

how about the MAX6126 ?
their app note looks impressive

7 ppm due to humidity change after a short power interruption?

"The glitch
shown at approximately 2400 hours corresponds to a rise
in humidity that occurred due to the backup power supply
not immediately turning on."

I fear I have enough bad (slow responding) humidity sensors in my ADC collection.

with best regards

Andreas

[Andreas]

Hello,

just for comparison: ADC#25 with AD586LQ under similar conditions.
Hysteresis is some uV (typically < 1 ppm) in this case and no visible ageing drift.

with best regards

Andreas

[slugrustle]

Not sure if someone else mentioned it or not, but ADR4550DEZ looks good.  Only trouble is the ceramic package ones don't seem to be available.

[iMo]

Hello,
first result from ADC#32 with REF7050 in dead bug mounting.

The DS shows pretty large initial drift. Wait 2-3w what will happen.
The hysteresis could be caused by the large aging drift, imho.

[miro123]

Hello,

first result from ADC#32 with REF7050 in dead bug mounting.

with best regards

Andreas

I don't fully understand the graph. I have few questions/remarks.
The graph looks very good at both ends between two cycles - T=10C and 40C . Do you perform some compensation of initial time drift?
Also going back and forth to 10C looks very good.

I have learned from AD AppNotes - First perform oil bath aging test, then T hysteresis tests. On such way you are looking at one parameter instead of many issues together. The thinks get worse when you look at many uncorrelated parameters together e.g. temperature humidity and aging
Best Regards,
Miro

[Andreas]

Not sure if someone else mentioned it or not, but ADR4550DEZ looks good.  Only trouble is the ceramic package ones don't seem to be available.

That is one on my todo list.
It was already mentioned in a different thread:
https://www.eevblog.com/forum/metrology/ti-new-ref54evm-evaluation-module-leaked/msg5181666/#msg5181666
From datassheet the ADR4550D looks really good.  (except for initial ageing). But hoping it will get better over time.

The DS shows pretty large initial drift. Wait 2-3w what will happen.
The hysteresis could be caused by the large aging drift, imho.

I fear no: the drift within 12 hours is much smaller than the hysteresis in one cycle.

I don't fully understand the graph. I have few questions/remarks.
Also going back and forth to 10C looks very good.

Attached a diagram with different colors for full cycles: (25-40-10-25)
Initially I started with 23 deg and a cold phase. (red)
The cold phase nearly returned with no hysteresis to 23 deg.
But after warm phase a large hysteresis is shown.
Somehow at 25 deg it goes to the old track.

Ageing then takes place during the next warm phase (green)
So the minimum voltage is shifted and also the end of the cycle.

The final measurement values (blue) show also a warm drift.

with best regards

Andreas

Edit: No there is no compensation of ageing drift in this case.
The first measurement is more or less to get an overview and to calibrate the on board NTC to the external temperature sensor.
Of course the hysteresis usually gets somewhat lower on following cycles. But not with nearly a magnitude higher to below 1 ppm.

[Andreas]

Hello,

first result from the other sample (ADC#31) with REF7050 directly soldered to slotted PCB.
As expected the hysteresis is larger than on dead bug mounted PCB. (18-21 ppm at lower temperatures).

But there is also an unexpected "jump" near 29 deg C.
And a very weird T.C. curve which is hard to be approximated.

with best regards

Andreas

[Kleinstein]

The datasheet suggests that there is some digital calibration / TC adjustment. For the 2nd sample it loops like a brakepoint in correction near 29 C.

The datasheet also gives rather high values for the hysteresistis. So at least they a honest in this aspect and the hysteresis does not come as a surprise.
There is a slight chance that the hysteresis gets significant smaller for a reduce temperature range.  The more normal use case is also with a slightly smaller temperature range. Of cause longer times at the temperature extremes (e.g. a few days in transport) may also increase the hysteresist.

[Andreas]

The datasheet suggests that there is some digital calibration / TC adjustment. For the 2nd sample it loops like a brakepoint in correction near 29 C.

Hello,
interesting theory.
it looks like there is a hysteresis on falling temperatures over ~ 7 degrees from 36 to 29 deg C before the jump.

But why does the jump exist only on falling temperature? and not on rising.
And why a 30 uV/3.333V (~9ppm Jump) within ~1 deg C for a 2 ppm/K reference?


with best regards

Andreas

[iMo]

The TC in REF70 is digitally compensated and specified with the box method from -40 to +125C. Inside the box it could be almost anything and bumpy, imho.

[TUMEMBER]

The TC in REF70 is digitally compensated and specified with the box method from -40 to +125C. Inside the box it could be almost anything and bumpy, imho.

Maybe that's why ?

[Andreas]

The TC in REF70 is digitally compensated and specified with the box method from -40 to +125C. Inside the box it could be almost anything and bumpy, imho.

Hello,

from which document do you get this information.

On the current datasheet there is only the hint of "temperature curvature correction" which is standard since 2nd and 3rd generation references.

with best regards

Andreas

[Kleinstein]

The block diagram shown a digital core. It is still a bit unclear what that means.

With quite some newer parts (e.g. e-trim OP-amps) they use some DACs instead of old style Zener zapping or laser trimming. This can still be essentially static working DACs, as a kind of digital trimmers. The idea is that trimming can be done relatively fine (zener zapping is limited), with multiple parameters and after encapulating in the case.  This is how they can get quite low offsets even with CMOS OP-amps (e.g. OPA192) in a plastic case.
The digital trim may allow for more parts to the temperature compensation, more than just absolute value, linear and curvature. I don't hink the correction would be with an ADC, math and than a correction, more like addition of correction terms and fixed DAC values to scale the amplitude for these correction terms. More terms allow for lower TC also over a large range.

The 2nd part looks like it has a rather poor voltage - temperature curve with quite some corrections applied and this includes also a rather steep section. Besides the "jumps / cusp near 29 C there also seems to be brake in the curvce at some 35 C and a bit unclear at 8 C.
The hysteresis part may effect the correction parts differently and thus the difference in the curve going up and down.

I would consider that 2nd part borderline - defective / worth going to the reject bin. It is alte least limited in the useful temperature range.

[Andreas]

Hmm,

I am somewhat confused ...   
some minutes later (omitting the first 1000 minutes for overview).

with best regards

Andreas

[iMo]

Years back chuckb made test with the ref7025
https://www.eevblog.com/forum/metrology/ref70-new-from-ti/msg3569115/#msg3569115
and he got 56ppm hysteresis while cycling 25..61C and back.

[Andreas]

Hello,

should have remembered that. I wouldnt have made a PCB especially for REF7050 in this case.
I fear I will at maximum mount the ADC31 also as dead bug style to see if the "dents" will disappear.

with best regards

Andreas

[Andreas]

Hello,

update to ADC32 (dead bug mounted reference)

https://www.eevblog.com/forum/metrology/stability-of-5v-references-compared-to-ad586lq/msg5278726/#msg5278726

after Offset Drift T.C. compensation and T.C. compensation.
The ageing drift is largely reduced.
The hysteresis is still there.

with best regards

Andreas

[Kleinstein]

It may be interesting if the hysteresis gets much better with a small temperature span. Normal use usually is quite a bit smaller. There is a slight chance that a smaller range could be much better, e.g. if there is a threshold for things like thermal stress before it really causes hysteresis.

[Andreas]

Hello,

ADC#31 after mounting the (same) REF7050 dead bug style:

see here for reference:
https://www.eevblog.com/forum/metrology/stability-of-5v-references-compared-to-ad586lq/msg5280709/#msg5280709

- There is a ~400 uV/3.333V shift 120 ppm (soldering drift?) between the PCB-mounted and dead bug mounted measurement.
- the dents do no longer show up (so probably was some interaction between PCB and reference)
- T.C. between 15 and 35 deg C (at thermally isolated reference so 10 to 30 deg C environment) is increased from ~3 ppm/K to ~6 ppm/K
- hysteresis is still too large (~14ppm) but now more near room temperature.

with best regards

Andreas

[branadic]

Looks not like a reference, but more like a t.c.-attractor.

-branadic-

[enut11]

Hi Andreas.
LQ chip available from Mainline Electronics UK, ebay item number 254576463764.
Enut11