Author Topic: Ultra Precision Reference LTZ1000  (Read 987912 times)

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Offline branadic

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Re: Ultra Precision Reference LTZ1000
« Reply #1250 on: January 03, 2016, 10:36:43 am »
I've measured a batch of several capacitors and found, that the 85°C types from Yageo deliver fair leackage currents <5nA after 24h forming in a combination of 2200µF/35V and 1000µF/25V that were finally used for the noise amplifier. 105°C types had decades worse leakage.
Wet tantal are hard to get and Sanyo Oscon deliver only small voltage ratings.
There was a document available, that delivers some explanation, but it's in german. (see attachement)
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Offline Andreas

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Re: Ultra Precision Reference LTZ1000
« Reply #1251 on: January 03, 2016, 09:40:35 pm »
The base of the temperature controller is mainly reproducing the noise of the reference, there should be only minor traces coming from the temperature noise. The better place to look at temperature noise would be the output of the OP.
Hello,

Do you really think that I am doing noise measurements at the base of the LTZ internal temperature sensing transistor?
I thought it is clear when I write J6 pin 12 as measurement point that it is the heater power transistor (BC639).
But obviously this is not the case.

@Branadic:
I do not think that OS-Con have low leakage current.
They are optimized for low ESR and high ripple current in low size.
I have some old stock 150uV/16V that I will charge over night.

With best regards

Andreas

Edit: measured values of leakage current as voltage drop over 100K resistor after 20 hours charging.
OSCON 150uF/16V (through hole, pink shrink tube, new old stock)
#1   1.6mV = 16nA
#2 11.7mV = 117nA
#3   0.7mV = 7nA

For 3200uF one would have to parallel 21 pcs of those to get the capacity.
« Last Edit: January 05, 2016, 04:56:21 pm by Andreas »
 

Offline Galaxyrise

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Re: Ultra Precision Reference LTZ1000
« Reply #1252 on: January 03, 2016, 09:49:55 pm »
Well the setup wiring is ok so that leaves a strange operation of the chip.
I'm looking at a puzzling behavior that may be related.  Started a separate thread for it here rather than lengthen this thread with back and forth over my circuit.  (but if it's interesting, I'll reproduce the conclusion here.)  Short version is that I'm seeing an effect on Pin4 from Pin6 even when I don't expect there to be one.
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Offline MK

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Re: Ultra Precision Reference LTZ1000
« Reply #1253 on: January 05, 2016, 06:36:44 pm »
A while ago I made myself a spice circuit of the LTZ1000 using some 2n5088/2n5089 parts for the small Q1 and Q2, just used a btz6.2 zener as the core zener just for modelling how it behaved, it seems prone to oscillation almost no matter what I did, could it all be oscillating quietly?
 

Offline Andreas

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Re: Ultra Precision Reference LTZ1000
« Reply #1254 on: January 07, 2016, 09:20:37 pm »
Hello,

@andreas, i have same "pop corn" problem before, and i didnt quite know the way to solve it.

if i tap on the SOT23 lightly with a insulator stick, it can trigger/reproduce the noise.

Just for noise testing even a more normal resistor would be OK to test a different current. Its allways the possiblity to have a certain current or temperature  the zener diode does not like. So it might be interesting to do a slow temperature ramp (e.g. 1 degree), while doing a longer noise measurement.

I did several tests on LTZ#5:
Knocking on critical components -> no additional events.

Changed current through Zener: 1K resistor in parallel to R1=120 R -> no change in behaviour.
Additionally changed temperature setpoint: 22k resistor in parallel to R5 = 1K -> the first measurements showed no popcorn noise events. Then I did my "last noise measurement". Result: extreme number of popcorn noise within this measurement.
The following measurements showed again numerous popcorn noise events.
So the problem was not gone. (only a "statistical" improvement).

I decided to built the 2 further references immediately to check wether the chopper (LTC2057) is the guilty.
So the 2nd device with LTC2057 (LTZ#6) showed no popcorn noise.
Whereas on LTZ#4 (with LT1013A) showed 1 single (small 0.35uV event = within 3 sigma limits) during 15*100 sec measurement time.

I tried to differentiate between OP-Amp and zener by measuring noise at the OP-Amp Output (the gate of the BF245C FET).
The interesting result is that the noise at this point is a factor 2.9-7.6 higher than at the zener.
The average relative amplitude on LTZ#5 between noise is factor 2.9
The average relative amplitude of the popcorn noise jump heigth is factor 2.0
So the probability is higher that the Zener is the guilty.

But anyway: I think I will try exchanging the current regulator OP first. (since it is cheaper).

With best regards

Andreas
 

Online Kleinstein

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Re: Ultra Precision Reference LTZ1000
« Reply #1255 on: January 07, 2016, 10:26:13 pm »
The transconductance of the BF245 is rather low compared to the load impedance, which is only the zener and 120 Ohms. So the sourcefollower will have an AC  gain of only about 1/3 to 1/2. This is why noise is higher at the OPs output.

However this hardly can explain more than a factor of 3. There might be excessive LF noise from the FET: the transistor in the LTZ and the OP will compensate for that - thus the noise of the FET would appear at the gate, which is the OPs output. Still I don't think the noise of the FET will be a problem as it will hardly make it to the output.

 

Offline Galaxyrise

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Re: Ultra Precision Reference LTZ1000
« Reply #1256 on: January 10, 2016, 10:26:49 pm »
So a possible explanation would be that the hfe of Q1 is significantly higher than that of Q2 for the active cirquit.
How would one safely measure hfe of Q1 in a LTZ1000?  My attempt worked for my mock ltz but gave a garbage value for the real thing.  (I wonder if I've killed another one, now.)
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Offline Galaxyrise

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Re: Ultra Precision Reference LTZ1000
« Reply #1257 on: January 10, 2016, 11:24:52 pm »
Why can't you just trust the data-sheet value of 200?  Anything you measure will be for your LTZ anyway-- and since there are always process variations, your value of hfe will not necessarily be the same as the typical data-sheet value, or as someone else's LTZ.
Gives me confidence that I understand what's going on and everything is as it should be.  Having gotten a garbage value demonstrates that at least one of those two is not correct.
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Offline 3roomlab

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Re: Ultra Precision Reference LTZ1000
« Reply #1258 on: January 11, 2016, 04:57:19 pm »
i have some OT Qn. did mickle T have a thread about how he modded his solartron with LTZ1k?
overclocked CPU and GPU are a waste of energy and time, it is highly energy + calculation inefficient vs watts. there is an entire influencer industry milking users off it, they call it "premium" but lifespans are short, oxymoronic crap , more like single use.
 

Offline Vgkid

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Re: Ultra Precision Reference LTZ1000
« Reply #1259 on: January 11, 2016, 05:31:33 pm »
i have some OT Qn. did mickle T have a thread about how he modded his solartron with LTZ1k?
I believe he modded his 7081. I have a document about it, look on here.
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Offline ManateeMafia

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Re: Ultra Precision Reference LTZ1000
« Reply #1260 on: January 12, 2016, 02:48:49 am »
Try here http://www.ko4bb.com/manuals/index.php

Search for 7081. The file is ~100MB.
 

Offline Vgkid

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Re: Ultra Precision Reference LTZ1000
« Reply #1261 on: January 12, 2016, 06:06:44 am »
^^^That looks like it, a very large djvu file.
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Offline Andreas

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Re: Ultra Precision Reference LTZ1000
« Reply #1262 on: January 12, 2016, 09:14:56 pm »

So the probability is higher that the Zener is the guilty.

But anyway: I think I will try exchanging the current regulator OP first. (since it is cheaper).


Hello,

I did exchange the current regulator OP (LTC2057) and the FET (BF245C).
-> no change. Still having the popcorn noise.
So before I exchange now the LTZ I will try if the noise cures when doing a run-in phase
with a higher temperature setpoint for some weeks.

Has someone experiences in this direction?

With best regards

Andreas
 

Online Dr. Frank

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Re: Ultra Precision Reference LTZ1000
« Reply #1263 on: January 12, 2016, 11:58:12 pm »
Hello,

I did exchange the current regulator OP (LTC2057) and the FET (BF245C).
-> no change. Still having the popcorn noise.
So before I exchange now the LTZ I will try if the noise cures when doing a run-in phase
with a higher temperature setpoint for some weeks.

Has someone experiences in this direction?

With best regards

Andreas

Andreas, don't do it!  :palm: :palm: :palm:
Yep, I have some -bad- experience in treating these LTZs with higher temperatures..

You will definitely have hysteresis, and after removing hysteresis, you will have bigger drifts the next 1-2 years, compared to a LTZ w/o excessive temperature increase.

Frank
 

Offline Andreas

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Re: Ultra Precision Reference LTZ1000
« Reply #1264 on: January 13, 2016, 07:32:13 am »
Hello,

@Frank: too late: I already put a 5K resistor between J6 Pin 10 + 11 to gently increase the setpoint.
I will not go above 15:1 (like HP) so dont worry.
It´s just trying to ride a dead horse. (I think I will have to exchange the LTZ anyway).

I have read somewhere that the ageing rate of zeners (probably 1N82x) is correlated to the noise.
I think that "popcorn noise" is meant. So this candidate will have anyway a higher ageing rate.
I will try to automate this: e.g. 10 sec high setpoint to 10 sec low setpoint.
I hope that if there is a fault in the die attach that then this may be cured by temperature cycling.

@3roomlab
No certainly not.
warm up time is around 500 ms to (near) steady state.
The popcorn noise events are 1 per minute in average.
(some minutes no event, other minutes up to 4 events).

After setting the setpoint 9 degrees higher there were no events for some minutes.

See also:
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg837667/#msg837667

With best regards

Andreas
 

Online Kleinstein

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Re: Ultra Precision Reference LTZ1000
« Reply #1265 on: January 13, 2016, 04:59:25 pm »
If it is the noise from the zener diode, I think chances are better to try a even higher current than higher temperature. Even if chances are not that good a lower current might be worth a try too, as this is a low risk try. Just for noise tests the current setting resistor does not have to be high stabilitiy. Just in case the popcorn noise is comming from the transistor inside the LTZ1000, one might try using the transistor with a slightly higher collector voltage (e.g. add a resistor (100 K range) from the regulated 7 V to the inverting input of the OP).

It is rather unlikely that high temperature burn in will change much. Though chances are there if you go to a range where significant dift occurs. However this irreversible - so it's more like a last chance.
 

Offline branadic

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Re: Ultra Precision Reference LTZ1000
« Reply #1266 on: January 13, 2016, 08:39:43 pm »
Thanks to our small volt nut meeting last saturday I'm now owner of one of Andreas LTZ1047B boards. So I started building up the circuit as far as I could.
Therefor I used our 3D printer to print a small spacer (material: thermoset) for the LTZ1000 (with 0.7mm holes) that keeps away airflow at the pins and increases the distance between pcb and reference to support long wires at the reference.

The Edwin G. Pettis LTZ resistor set is already placed and thermally coupled with some copper tape.

There are still some components missing, that I need to order as quick as possible to get the beast finished.  :-+
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Offline TiN

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Re: Ultra Precision Reference LTZ1000
« Reply #1267 on: January 14, 2016, 04:48:58 am »
That Jamicon capacitor hurt's my precision eye  :P.
Nice job, I see you used jelly-bean 2057 too. Don't you love that little guy?
Fresh LTZ too.

What's your plan on usage for this module?
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Offline Andreas

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Re: Ultra Precision Reference LTZ1000
« Reply #1268 on: January 14, 2016, 06:54:42 am »
Hello,

That Jamicon capacitor hurt's my precision eye  :P.

never mind it´s only to calm down the on board (low drop) voltage regulator.
It will do it´s job.

@Branadic: nice stand off.
Do you have any data sheet about the thermoset material?

But I never expected that you would divide up the 400K resistor into 2 parts.
I would use this guy (which is within a 1% tolerance).
http://www.reichelt.de/1-4W-1-100-k-Ohm-976-k-Ohm/METALL-402K/3/index.html?ACTION=3&GROUPID=3080&ARTICLE=11793&SEARCH=402k&OFFSET=16&WKID=0&

But I personally think that the tolerance of this resistor is not critical.
(except when you adapt it especially on each individual LTZ).

With best regards

Andreas



 

Online Kleinstein

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Re: Ultra Precision Reference LTZ1000
« Reply #1269 on: January 14, 2016, 05:45:33 pm »
The suitable resistor for the "400 K" resistor will rather much depend on the LTZ1000 unit, possbly the OP used and also on the thermal design and likely the temperature setpoint (would expect higher resistors at lower temperature) used.  It is a try to compensate the residual temperature coefficient / imperfection of temperature control. So the right value can change a lot - should be more something in the 200 K - 5 M range depending on the individual unit and thermal setup. So I would not expect to need a tight tolerance and also no super low drift - especially with just the first guess of 400 K is used.

The more interesting question is to find a procedure to find (measure) the best value for a give setup - might need to measure temperature coefficient and optimize. So this step might need quite some time, especially without good procedures to follow.
 

Offline branadic

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Re: Ultra Precision Reference LTZ1000
« Reply #1270 on: January 14, 2016, 10:17:17 pm »
Quote
@Branadic: nice stand off.
Do you have any data sheet about the thermoset material?

But I never expected that you would divide up the 400K resistor into 2 parts.
I would use this guy (which is within a 1% tolerance).
http://www.reichelt.de/1-4W-1-100-k-Ohm-976-k-Ohm/METALL-402K/3/index.html?ACTION=3&GROUPID=3080&ARTICLE=11793&SEARCH=402k&OFFSET=16&WKID=0&

But I personally think that the tolerance of this resistor is not critical.
(except when you adapt it especially on each individual LTZ).

With best regards

Andreas

As I sad, I used what I had lying around, but as I have to order some parts the 400k made of two 200k resistors will be replaced by 402k. However, 400k in value is somewhat uncommon. I wonder why the used that special value instead of something available in the e series, if the it is not that important.  :-//
The datasheet for the material is confidential, but as said it's a thermoset.
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Offline Andreas

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Re: Ultra Precision Reference LTZ1000
« Reply #1271 on: January 14, 2016, 11:00:40 pm »
Hello,

again some measurements.
PSRR on LTZ#3. (With LT1013A)

For this I have supplied the LTZ at the output of the voltage regulator. (so without stabilisation).
Yes, the LT1763 is one of the few regulators which can be used this way without damage.

From 8.75V to 18.25V the change is around -13uV at ADC input (after 2:1 divider)
 so -26 uV or less than 4 ppm over a 9.5V input range.
Giving -0.4ppm/V for the LTZ cirquit.

below 8.3V the output voltage is in dropout.
Until 8.3V it is stable.
 (ok should have waited some more time to stabilize between switching on
and starting measurement from 9V downto 8.3V)

with best regards

Andreas
« Last Edit: January 14, 2016, 11:05:57 pm by Andreas »
 

Offline Andreas

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Re: Ultra Precision Reference LTZ1000
« Reply #1272 on: January 16, 2016, 08:03:58 am »
Hello,

next measurements: PSSR on LTZ#5
(with LTC2057 which has Rail to Rail output)

Same setup as on LTZ#3

From 8.5 to 18.5V the change is around -11uV  at ADC input
so 22uV or around 3 ppm over a 10V span.
Giving -0.28 ppm/V as regression curve.

Dropout starts (as expected due to Rail/Rail output)
at the lower value of around 7700mV
Until 7750mV the unbuffered output is stable.

with best regards

Andreas
 

Offline ltz2000

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Re: Ultra Precision Reference LTZ1000
« Reply #1273 on: January 16, 2016, 11:05:46 am »
PSRR on LTZ#3. (With LT1013A)

Many thanks!
 

Offline Andreas

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Re: Ultra Precision Reference LTZ1000
« Reply #1274 on: January 16, 2016, 11:35:30 am »
PSRR on LTZ#3. (With LT1013A)

Many thanks!

But be aware that I have a additional BF245C
against the original cirquit for the current regulator.
Without this the drop out voltage will be much higher.

With best regards

Andreas
 


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