LM399 based 10 V reference

[zhtoor]

2. use some kind of delamination procedure (methods required here!) to strip them off the epoxy/plastic encapsulation.
3. characterize / select these de-laminated parts for an averaging type voltage reference in a custom heating assembly.

Hello,

I also do not understand why you want to delaminate the epoxy.
I would either use the metal can devices or put the epoxy types into a hermetically sealed housing.
Perhaps with some baking of the epoxy before sealing (with glass).

To reach the LTZ 1/f noise spec you would have to average ~16 LM329 devices (selected for low noise of ~4-5 uVpp)
There was a teardown with pictures of a commercial LMx29 reference here in the board somewhere.
I would start there. perhaps you get the handbook with schematics.

good luck

with best regards

Andreas

Hello.

first of all, thanks for the response.

second.

i wanted to delaminate the epoxy to establish a better temperature distribution to the references being averaged, and also to give me a bigger
latitude to confine a relatively large number of these in a small space (16 to 64pcs, dont know yet).

regards and thanks.

[zhtoor]

Just curious- you can still buy all manner of 1Nxxxx series zero TC zeners. I've made some really decent references with those, an OP-07 and a few resistors, the standard self-biased circuit. Is a 2DW23x really any better than 1N821 or 1N45xx or 1N935-938, or just cheaper?

Dear Sir,

thanks for the response.

1N829 is available at ~USD 12 a piece., quite expensive.

http://www.digikey.com/products/en/discrete-semiconductor-products/diodes-zener-single/287?k=1N829&k=&pkeyword=1N829&pv69=80&mnonly=0&newproducts=0&ColumnSort=0&page=1&quantity=0&ptm=0&fid=0&pageSize=25

which is probably a selected 5.2V zener in series with a regular forward biased diode, both selected to form a concave curve of voltage variation vs. temperature,
and the valley coinciding with around 25 degC.

if the same thing could be done by characterizing a bunch of 5.2V zeners and regular -2,2mv/degC diodes, could be interesting.

Regards and thanks.

[Conrad Hoffman]

Just curious- you can still buy all manner of 1Nxxxx series zero TC zeners. I've made some really decent references with those,

Hello,

did you measure 1/f noise of the zener?
I got some 1N829A of different manufactures.
NOS of Motorola and ST (cheap) and some new APD (5 EUR / piece).

I measured different noise from device to device (typical 1.7-3uVpp for Mot+APD)
and very different between ST (up to 22uVpp) and the others.

with best regards

Andreas

I haven't, but a friend who built commercial equipment did, and he said something interesting. It seems if you select the quietest parts from a batch, those will also have the least long term drift.

The zero tc diodes seem to have gotten quite expensive, so maybe selection isn't a good strategy these days. It does make me wonder if one could pot together pairs of conventional (read cheap) zeners that were selected for noise- roll your own!

[Andreas]

I haven't, but a friend who built commercial equipment did, and he said something interesting. It seems if you select the quietest parts from a batch, those will also have the least long term drift.

Hello,

thats also something that I read somewhere.
But I still do not know if the 1/f noise or the popcorn noise is meant.
I guess its the popcorn noise since it is related with impurities / imperfections of the silicon.

With best regards

Andreas

[zhtoor]

Just curious- you can still buy all manner of 1Nxxxx series zero TC zeners. I've made some really decent references with those,

Hello,

did you measure 1/f noise of the zener?
I got some 1N829A of different manufactures.
NOS of Motorola and ST (cheap) and some new APD (5 EUR / piece).

I measured different noise from device to device (typical 1.7-3uVpp for Mot+APD)
and very different between ST (up to 22uVpp) and the others.

with best regards

Andreas

I haven't, but a friend who built commercial equipment did, and he said something interesting. It seems if you select the quietest parts from a batch, those will also have the least long term drift.

The zero tc diodes seem to have gotten quite expensive, so maybe selection isn't a good strategy these days. It does make me wonder if one could pot together pairs of conventional (read cheap) zeners that were selected for noise- roll your own!

that is *EXACTLY* what i had in mind sir !

please tell me how !

regards.

[zhtoor]

I haven't, but a friend who built commercial equipment did, and he said something interesting. It seems if you select the quietest parts from a batch, those will also have the least long term drift.

Hello,

thats also something that I read somewhere.
But I still do not know if the 1/f noise or the popcorn noise is meant.
I guess its the popcorn noise since it is related with impurities / imperfections of the silicon.

With best regards

Andreas

sort of "harvesting" through these:-

http://www.digikey.com/product-detail/en/fairchild-on-semiconductor/1N5232BTR/1N5232BFSCT-ND/458917

5.6V zener $24/1000 pcs.

maybe you could characterize these for noise performance and tempco curves vs. temperature.

regards.

[Kleinstein]

Form comparison of the Chinese DW232 from different sources, there seems to be different levels of noise. If you get the wrong type of zener, you might end up with 1000 relatively noise zeners and not a single low noise one. If you are combining diodes it might also be an option to combine two zeners and one forward diode to get something like a 11,8 V (2x5.6+0.6) reference. One could also do it with a transistor instead of a diode (much like the LTZ1000 internal circuit) and this way reduce amplifier noise and drift.

As long as the parts operate at a constant power level, it should not be so bad having them on different chips. Just make sure the temperature is steady - so a good thermal setup is essential to avoid LF noise from temperature fluctuations.

[julian1]

i was looking at NZX6V2 which is available @ digikey, and according to its datasheet,
the tempco is +1.5 to 2.5mv/C at 1 to 5ma zener current. Now if this zener family is selected/characterized
for noise performance and paired with a regular silicon diode or a lownoise transistor connected in diode config,
having a tempco of ca. -2.2mv/C, there shall be a "sweet spot" between 1ma and 5ma where these tempco's
shall cancel out completely, and now if properly aged components are used, we *may" have one lownoise (?)
source of steady reference.

Just to to note - this is exactly what the 2DW23x component is.  Like this - but ignore the resistor.



Two diodes in series in a back to back configuration. So at a certain current - somewhere between 5-30mA depending on device - the tempco of the two diodes are in balance with one another.

The nice thing about the 2DW23x versus implementing the same thing using two discrete diodes, is that the diodes are on the same silicon substrate - which minimises small temperature gradients and differences.

At that point it is also still beneficial to ovenize or stabilize the device temperature to create a better reference - since the TC0 balance point is subject to second-order effects and is kind of "peaky".

[enut11]

Hi All
I have just taken delivery of four LM399 ICs and want to use one on a 10v ref PCB.
Is there a way of testing the chips to select the best one before soldering to the PCB?
enut11

Edit: I think I have answered my own question. There is no simple way to simulate the conditions of a ref circuit without testing each one in turn in the same ref circuit. So I think I need to socket the zener.

[IconicPCB]

Enut11,

I think this comes to the question of "pre ageing " components... it does not necessarily work.
Without soldering.. there is no way of knowing just how the component will behave post final assembly.
My two cent-i volts of noise

[David Hess]

You could test them for temperature coefficient , noise level, and for popcorn noise.  Testing for popcorn noise can take a while.  Long term drift is more difficult because it is affected by mounting.

[mimmus78]

Any interesting project with a blown heater lm399? I connected backwards ...

Inviato dal mio Nexus 6P utilizzando Tapatalk

[Alex Nikitin]

Any interesting project with a blown heater lm399? I connected backwards ...

Inviato dal mio Nexus 6P utilizzando Tapatalk

If the voltage reference part is still OK, you have now essentially LM329 in a metal can. Measure the tempco at room temperature, you might got lucky and have now a nice stable low current voltage reference, possibly with a somewhat lower noise than a heated LM399. If the tempco is high (10-20ppm/C) but reasonably linear around 25C, you may attempt to compensate for it with some diodes, as I did for my LT1021 mini-reference.

Cheers

Alex

[Andreas]

You could test them for temperature coefficient , noise level, and for popcorn noise.  Testing for popcorn noise can take a while.  Long term drift is more difficult because it is affected by mounting.

I second this.

But in every case I would do longterm testing.
The best would be soldering in final configuration.
(see also attached picture with much larger stray of the daily measurements against the soldered solution).

Then monitor the devices at least daily and record drift for at least some kHr.
 + calculate standard deviation over the last 2 kHrs to see which reference has lowest day to day drifts.
similar to here:
https://www.eevblog.com/forum/metrology/lm399-based-10-v-reference/msg796829/#msg796829
with best regards

Andreas

Edit: corrected link

[mimmus78]

Thanks guys,

I will do some of this experiment when I will free from my ltz project that is sucking me up :-).

I wonder how Andreas manage to track down his references day by days for years.

[enut11]

Hi all
I am sorting through some LM399 chips and measuring Vz. Variation so far is 6.86v to 7.15v.

Does this mean anything apart from needing different trimming resistors to get the required 10v buffered output?
enut11

[mimmus78]

So this is noise of the lm399 with blown heater as read by 3458a at 100NPLC ... 3 times better than the other lm399 with heater.

[mimmus78]

Hi all
I am sorting through some LM399 chips and measuring Vz. Variation so far is 6.86v to 7.15v.

Does this mean anything apart from needing different trimming resistors to get the required 10v buffered output?
enut11

The ones with lower voltages seems to be better ... just read thorough the thread :-)

[IconicPCB]

Mimmus,

If you think that lm399 with a blown heater is a better choice for You, You should get hold of an LM329 ( zener half of LM399 no heater ) and run a test with it.
As a comparison

Element14 offer LM399 rated at 2% initial accuracy, and a temp coefficient of 0.3ppm/C at AUD 18.60

LM329 is offered as

Texas instruments product  5% initial accuracy  and 50ppm/C temp cpefficient AUD 1.76
and
Linear Technology product unspecified initial accuracy  and 15ppm/C temp coefficient AUD 5.00

Even the most rudimentary of ovens should be able to bring in the 50ppm /C  specification into check.

[Theboel]

I believe every LM399 has their own characteristic when You measure it with 3458A. I have 16 pcs LM399 that already run 24/7 for 1 year even the voltage is "different" the closed one are 3,4mV different, noise is also different. data sheet number is the worst condition and I do not found any exceed the datasheet. so in my opinion if You like to know how good or bad the LM399 with or without heater the best way is compare the healthy one with heater on and then turn the heater off.
surely I like to know how good the LM399 if the heater is turn off when You measure with 3458A.   

[Alex Nikitin]

Mimmus,

If you think that lm399 with a blown heater is a better choice for You, You should get hold of an LM329 ( zener half of LM399 no heater ) and run a test with it.
As a comparison

Element14 offer LM399 rated at 2% initial accuracy, and a temp coefficient of 0.3ppm/C at AUD 18.60

LM329 is offered as

Texas instruments product  5% initial accuracy  and 50ppm/C temp cpefficient AUD 1.76
and
Linear Technology product unspecified initial accuracy  and 15ppm/C temp coefficient AUD 5.00

Even the most rudimentary of ovens should be able to bring in the 50ppm /C  specification into check.

The main difference is that current LM329 offers are all in a plastic case, so the long term stability is not guaranteed, especially if the humidity varies. LM399 is always supplied in a metal hermetic case and provides for a much better stability, even if used not heated. I have some LM129AH in a metal case and selected for a low tempco, one day I'll try to build a reference on 3-4 of these. My mini-reference based on LT1021CMH chip in a metal case so far is quite stable (over last three weeks the drift is less than 2ppm and that is a conservative estimate) even with a couple of thermal cycles from 15C to 40C and some hours travelling in my backpack outdoors (<5C) .

Cheers

Alex

[mimmus78]

I believe every LM399 has their own characteristic when You measure it with 3458A. I have 16 pcs LM399 that already run 24/7 for 1 year even the voltage is "different" the closed one are 3,4mV different, noise is also different. data sheet number is the worst condition and I do not found any exceed the datasheet. so in my opinion if You like to know how good or bad the LM399 with or without heater the best way is compare the healthy one with heater on and then turn the heater off.
surely I like to know how good the LM399 if the heater is turn off when You measure with 3458A.

Well I can only compare it with a good one LM399 (got from a broken K2000). This heated
LM399 has not drifted at all in 2 months so I'm not going to touch it.

Anyway this blown LM399 seems enough stable ... I think I will find the zero tempco point and
than use it in some oven project I have in mind. Bob Pease does not recommend to run LM399
without the heater as it leads to instability ... I guess this cannot be applied when the heater is
blown.

[branadic]

Thanks to Andreas here is a 24h + x measurement taken with Keysight 3458A at 100NPLC of my may years running LM399.
There is some related drift, but I can't say if this is due to a change of temperature in the controlled lab, if it is drift by the reference itself or if it is due to the drastical change in weather from yesterday morning (calm)  til this morning (stormy with 80km/h) and thus a change in ambient pressure. The ambient monitoring system is currently in use in another lab
However, after removing the drift component by a parabolic function the mean is 10.0017577V with a standard deviation of 1µV. My reference obviosly shows popcorn noise in the order of ~3µV.
I plotted Allan Variance before and after removing the drift component... need help to interprete the charts. I attached the original data, so maybe someone wants to analyse them and give some feedback?

EDIT:
Removed reference and added a short at the input of the 3458A, to see how noise compares in this situation. After a small thermal settling time of the short the noise is only a few hundred nV (still 100NPLC @10V). So the popcorn is proven to be from my LM399. Seems it's time to activate my LTZ and take some 24h hour measurements.

[Galaxyrise]

I think I will find the zero tempco point and
than use it in some oven project I have in mind. Bob Pease does not recommend to run LM399
without the heater as it leads to instability ...

zero TC temperature, you mean?  From my measurements in the past, that is likely to be quite warm, and most of the ones I measured didn't have a zero slope in the temperature range I put them through.

[Cerebus]

... or if it is due to the drastical change in weather from yesterday morning (calm)  til this morning (stormy with 80km/h) and thus a change in ambient pressure.

The air pressure here at my place in London dropped from approx 1018 mbar on Wednesday midday to 995 mbar by midday today - that's a 2.25% change, not insignificant.