ADR1399 reference

[iMo]

Is there any recommendation what type of the 1uF (ser 5R1) output capacitor should be used?
Foil or MLCC?

[Kleinstein]

The capacitor should not be hat critical. Even leakage is not a problem. When using MLCC I would plan for 2 x 1 µF to conpensate for the drop in capacitance under voltage and the 1 µF value is already on the low side to start with.

[Andreas]

Hello,

I have no issues with 1uF/50V X7R in 0805

with best regards

Andreas

[iMo]

@Andreas: inspired by your low noise 399 in your 34401A I put the HP399 off my DMM and been just doing some measurements..  Thinking to replace it with something better, currently running the DMM with a pops free LM399H, but thinking about one of my 1399 (<2uVpp).. Not sure I've been doing the right thing with my DMM, anyhow.. 

[Kleinstein]

If one has a rather rare LM399 without the typical popcorn noise, this would be a relatively low noise ref. Not sure that the ADR1399 is better than this. Some the LM399 still have rather rare jumps from the popcorn noise (I have one that is at about 1 jump per hour) - this can be great for some short time tests, but bad for other (no averaging for many tests, just shifting the noise to even lower frequencies).

The HP34401 also has a relatively noisy ADC. Though not directly comparable, the ADC noise can be limiting on the shorter time scale. To a large part there is not much one can do about it, as it's the somethwat limited resolution / quantization noise. Significant lower noise would need more like a redesign of the ADC.
With a well aged reference there is also low dirft - a new ADR1399 would need quite some time to get the drift rate of a LM399 with some 10000 hous of use.

[iMo]

I know, but - see below (the same setup), I will run the pops free LM399H#2 (1500h BI) over night.. Both 1399 (0h BI) I have are half of the LM399H#2 noise..

[Kleinstein]

Looking at the standard deviation of a 7 V ref reading is bit unusual. It still reflects the ref. noise, but only for a limited times scale of some 4 - 400 seconds. So more normal way would be to look at the alan deviation.
Anyway the difference is not that large. It is mainly having the jumps in the external LM399 ref and less or smaller jumps for the ADR. One would always see a combination of both references: The good lm399 in the 34401 and than either a more normal LM399 or the slightly lower noise ADR1399.  The fact that there is quite some difference shows that the reference in the meter is way better than normal. With a more normal ref. in the meter one would not see much difference (70% noise even with a noise free external ref., though the way the test is done may be more sensitive to peak then RMS noise).

Even for the relatively long time scale use in the test, the ADC noise is still a good part of the noise.

[iMo]

That is 10V external Vref. Both HP399 and LM399 are the 34401A's refs (inside the meter). The peaks in the STD show where a reference shifted its voltage abruptly (or it is EMI). Those pictures are not about any stability over time..

I have the data thus tomorrow, after the Starship's orbital flight, I will show you ADEV/MADEV as well

But sure, I do understand the replacement of the old HP399 with the fresh ADR1399 is tricky.. 

PS: CONT in the ADR1001 thread..

[diodak]

The capacitor should not be hat critical. Even leakage is not a problem. When using MLCC I would plan for 2 x 1 µF to conpensate for the drop in capacitance under voltage and the 1 µF value is already on the low side to start with.

What about the capacitor itself in parallel (instead of the RC circuit) according to the datasheet:
"Another single element passive that works directly with the ADR1399 is a 10 μF tantalum capacitor, even though the series resistance can
measure less than 5 Ω on an impedance analyzer."
Has anyone checked this?

[dietert1]

I did not try that as i think the better solution is a low leakage cap with a known resistor instead of unknown capacitor ESR. Trying to save a 1 cent part on a 15 $ reference?

Here i have a three month log of the ADR1399 SMD evaluation kit i got one year ago. It got an outer oven at 38.2 °C. These are 4 second measurements with residual TC corrected. The log shows a drift of about 1.4 ppm and the internal temperature of the P6048 in red. One can assume the drift of about 1.3 ppm is caused by the Vishay NOMC divider used for the 10 V gain stage. Maybe a confirmation of results Andreas showed above.

Regards, Dieter

[ivo]

Is there any recommendation what type of the 1uF (ser 5R1) output capacitor should be used?
Foil or MLCC?

It's a 1uF good MLCC + 5.1R resistor, AFAIK essentially to emulate a tantalum cap, same with older regulators wanting tants/ECs to settle on their output pin and you can generally pull the same trick with them

In the LM399 datasheets they advise you can do a similar thing with the heater: you can add 10~500R above it to limit the current draw on initial heatup, but to do so you must add a 2.2uF *tantulum* cap across it.

Trying to save a 1 cent part on a 15 $ reference?

My guess is because people don't want to have to deal with production scale soldering polypropylene (can't stand up to high soak temps) if they don't have to, and prefer to save cost on a tant. And yes two 1 cent parts vs a 10-50c part is a big difference!

[Andreas]

Hello,

update from ADR1399 PCB#2 now at 3 kHrs for the metal can devices (KHZ) and 3.1 kHrs for the LS8 devices (first 100 hours not shown):

See also
https://www.eevblog.com/forum/metrology/adr1399-reference/msg5145858/#msg5145858

The values are all temperature compensated (temperature sensor at the bottom of the hammond die cast housing)
Now the LS8 devices, which started with negative slope for ageing, trend to a slow upwards ageing slope like the TO-46 metal can devices.

with best regards

Andreas

[Andreas]

Hello,

update of ADR1399LS8 on PCB#1 ageing 7kHr after putting into Hammond die cast enclosure and with temperature compensation (sensor on bottom of the hammond case)
see also
https://www.eevblog.com/forum/metrology/adr1399-reference/msg5152335/#msg5152335


The ADR1399LS8 have now 10.3 kHrs in total operating time. Tempco is calculated out for the ageing curves.
These LS8-devices are drifting upwards.

The voltage shift at the 2 LM399 (only for comparison) occurred after repair on the output connector. (while operating the cirquit).
The investigation of the PCB did not give a obvious damage.
So I decided to replace the multiplexer for the LM399. This was obviously the reason for the defect as the readings reverted to the old level.
For the future I will drop the defective readings.

with best regards

Andreas

[Andreas]

Hello,

update of ADR1399LS8 on PCB#1 ageing 8kHr after putting into Hammond die cast enclosure and with temperature compensation (sensor on bottom of the hammond case)
see also
https://www.eevblog.com/forum/metrology/adr1399-reference/msg5226999/#msg5226999


The ADR1399LS8 have now 11.3 kHrs in total operating time. Tempco is calculated out for the ageing curves.
These LS8-devices are drifting upwards.

I had again a 5-6 ppm voltage shift on the 2 LM399 (only for comparison) on the 2nd Multiplexer (MAX4052A).
This time I had no obvious reason for the shift. So it was very unreasonable that the Multiplexer should have died again.
I reflected what I did last time:
- Switching power off and on (on another desk) to do some measurements.
- Measurements did not show any obvious error.
- Exchange the MAX4052A. (with power off).
- reassembling and putting all back to the measurement desk.

So I decided to do power cycling only and actually this "cured" the 5-6 ppm voltage shift.
Obviously there is some "latchup effect" which affects the upper channels.

But what can the reason for this latchup effect be?
I had introduced some level shifters to reduce the self heating of the multiplexers when having 5V logic levels.
But the level shifters are relatively high ohmic (BSS138 with 330K pull-up resistors on the 15V side) to reduce self heating.
Simulation with a similar FET (BSS123) showed around 20 us rise time with 20 pF for wiring and input capacitances of the multiplexers.
Should this be the reason for the latchup-effects?

with best regards

Andreas

[Andreas]

Hello,

update from ADR1399 PCB#2 now at 4 kHrs for the metal can devices (KHZ) and 4.1 kHrs for the LS8 devices (first 100 hours not shown):

See also
https://www.eevblog.com/forum/metrology/adr1399-reference/msg5226966/#msg5226966

The values are all temperature compensated (temperature sensor at the bottom of the hammond die cast housing)
The LS8 devices continue to trend to a slow upwards ageing slope like the TO-46 metal can devices.

If I look closer there are also 0.5-1 ppm jumps on the measurements.
One jump in down direction is on the same day as the power cycling together with PCB#1 (same transformer).

so I started to investigate (see zoomed diagram).
And actually: every time when I did a power cycling (half a minute followed by >15 minutes warm up time) the measurements started at lower levels.
After one measurement cycle mostly the higher level was again active.
So also here I have a less pronounced "latchup effect" of 0.5-1 ppm.

So the question arises: Are there any multiplexers like MAX4052A which can be used as replacement (hoping that there will be no latch up effect)
- low leakage current
- operating from 12-15V (single supply)
- in SO-16 package with same pinout as 4052 devices
- at best with integrated low power level shifters from 5V to 15 V

with best regards

Andreas



with best regards

Andreas

[Kleinstein]

A possible choice for the MUX chips could be the relatively new TMUX4052. The specs are rather loose because it is a cheap part (so not much testing done), but the typical performance is still expected to be relative good. They accept a low control level (e.g. 2 V) at least.  The DG4052 should be similar with tighter specs.

[Andreas]

A possible choice for the MUX chips could be the relatively new TMUX4052.

Hello,

Electrically it would fit (I think). But I did not find a SO16 package. Or did I overlook something?
(I do not want to resolder the references, only the multiplexers).

The DG4052 might be a replacement.

with best regards

Andreas

[Mickle T.]

A simple, general-purpose, dual-voltage (10V and 1V) reference based on the ADR1399 in a TO-46 package. Temperature coefficient <0.2 ppm/°C (10 V), noise amplitude 0.25 ppm p-p (0.1-10 Hz). Resistors are selected with TCR 0.2...2 ppm/°C.

https://youtu.be/guZnwp_DdUM

[ivo]

I swear most people's definitions of "simple" differ wildly from mine on this board 😅

[dietert1]

Yes, it seems to be more like a calibrator for voltage, current and resistance. Very nice.

Regards, Dieter

[Andreas]

Hello,

update from ADR1399 PCB#2 now at 5.4 kHrs for the metal can devices (KHZ) and 5.5 kHrs for the LS8 devices (first 100 hours not shown):

See also
https://www.eevblog.com/forum/metrology/adr1399-reference/msg5303665/#msg5303665

I have exchanged the MAX4052A multiplexers against standard HEF4052 (NXP) CMOS devices.
As result ther is a relative large jump on all references.
But also the "ageing" slope has changed significantly on all channels (mostly near zero).

So I fear that up to now I have measured the "ageing" of the MAX4052A instead of the references.
That also would explain the difficulties with my "position dependant drift".
I think that the MAX4052A are not usable for higher supply voltages than ~10-12V since I never recognized something unusual with 5V.

Should have used a relay multiplexer instead?
In the mean time I also have some DG4052 to give them a try.

with best regards

Andreas

[CalibrationGuy]

A simple, general-purpose, dual-voltage (10V and 1V) reference based on the ADR1399 in a TO-46 package. Temperature coefficient <0.2 ppm/°C (10 V), noise amplitude 0.25 ppm p-p (0.1-10 Hz). Resistors are selected with TCR 0.2...2 ppm/°C.

https://youtu.be/guZnwp_DdUM

This is a beautifully executed project. How long did this simple project take? How much did it cost you when all is said and done? Anyway, thanks for sharing.

PS - It costs my lab over $2700 per 3458A to backup our numbers. Voltage tests here are a bit subjective because even a Keysight ISO17025 calibration has an uncertainty of 1.1ppm.

[ivo]

I wonder if anyone with capable equipment, would be interested in testing if there's any appreciable difference in noise, and tempco ppm sweeps, over different reference currents? Say 3mA/6mA/10mA?

[CalibrationGuy]

I wonder if anyone with capable equipment, would be interested in testing if there's any appreciable difference in noise, and tempco ppm sweeps, over different reference currents? Say 3mA/6mA/10mA?

If such a request were made, you would have to clearly define what tests you would want including tolerance, number of samples, test conditions, etc. People who have labs are usually busy people. *cough* *cough*

TomG.

[iMo]

I wonder if anyone with capable equipment, would be interested in testing if there's any appreciable difference in noise, and tempco ppm sweeps, over different reference currents? Say 3mA/6mA/10mA?

The "zener current" inside the 1399 is set to a specific "constant value" by ADI, the same as with 399 (the chip is almost the same). You cannot change that current from outside.