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Offline BU508ATopic starter

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new voltage reference from MAXIM
« on: June 11, 2016, 05:59:44 pm »
Hello,

I received today a newsletter from MAXIM. Seems, they have a new voltage reference:

https://www.maximintegrated.com/en/products/analog/voltage-references/MAX6126.html

From their website:
************************snipp***********************************
Key Features

    Ultra-Low 1.3µVP-P Noise (0.1Hz to 10Hz, 2.048V Output)
    Ultra-Low 3ppm/°C (max) Temperature Coefficient
    ±0.02% (max) Initial Accuracy
    Wide (VOUT + 200mV) to 12.6V Supply Voltage Range
    Low 200mV (max) Dropout Voltage
    380µA Quiescent Supply Current
    10mA Sink/Source-Current Capability
    Stable with CLOAD = 0.1µF to 10µF
    Low 20ppm/1000hr Long-Term Stability
    0.025? (max) Load Regulation
    20µV/V (max) Line Regulation
    Force and Sense Outputs for Remote Sensing
************************snipp***********************************


Andreas
“Chaos is found in greatest abundance wherever order is being sought. It always defeats order, because it is better organized.”            - Terry Pratchett -
 

Offline uncle_bob

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Re: new voltage reference from MAXIM
« Reply #1 on: June 11, 2016, 07:39:38 pm »
Hi

Not bad, but not great either. There are now other chips on the market that will beat it noise and stability wise. It was a bit more interesting a while ago.

Bob
 

Offline uncle_bob

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Re: new voltage reference from MAXIM
« Reply #2 on: June 11, 2016, 07:51:18 pm »
Here is a paper that is about a study that was done on a small collection of reference chips-- including the MAX6126.  It did fairly well in the tests, but of course as always, it would never beat an LM399 or an LTZ1000(A) for hysteresis, temperature, humidity, or time drift.

ANY unheated reference IC will experience hysteresis with large temperature swings.  The hermetic packages do better with this, but it is not totally eliminated.  The LM399 has almost no hysteresis, and the LTZ1000A has a little more than the LM399-- but both of these are orders of magnitude better than ANY unheated chip [including the LTFLU-1].

This is OK, if the reference fills your need and the various drifts [when added together] are within the specs that you are looking for.

Hi

Paper ? (link appears to be missing :) )

I agree with everything you have said. My only point is the missing link.

Bob
« Last Edit: June 11, 2016, 07:54:34 pm by uncle_bob »
 

Offline necessaryevil

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Re: new voltage reference from MAXIM
« Reply #3 on: June 12, 2016, 03:02:50 pm »
Yeah, the MAX6126 is a nice one. Forum member Blackdog  made a voltage reference using four of them in parallel.  Search the forum! You should also check out the LT1021.

Do heated chips really not suffer from hysteresis? If they do, it will be worse than non-heated chips, because the heating will cause them to go through more temperature cycling at turn-on/switch-off.
 

Offline uncle_bob

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Re: new voltage reference from MAXIM
« Reply #4 on: June 12, 2016, 03:23:28 pm »
Yeah, the MAX6126 is a nice one. Forum member Blackdog  made a voltage reference using four of them in parallel.  Search the forum! You should also check out the LT1021.

Do heated chips really not suffer from hysteresis? If they do, it will be worse than non-heated chips, because the heating will cause them to go through more temperature cycling at turn-on/switch-off.

Hi

If the heated chip is powered up during the temperature cycle, the die sees much less "delta T" during the cycle. The chip does indeed change the amount of power into the heater. That change *does* have an impact. It is much less than the impact of a cycle on an un-heated part. Indeed the ideal case would be a heated part inside a heated enclosure. That has it's problems as well ....

Bob
 

Online Andreas

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Re: new voltage reference from MAXIM
« Reply #5 on: June 13, 2016, 06:45:42 pm »

I received today a newsletter from MAXIM. Seems, they have a new voltage reference:


Hello,

if you really want a "new" (old) voltage reference you could try the brand new LT1027 in hermetically LS8 package.
http://www.linear.com/product/LT1027LS8

with best regards

Andreas

 
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Offline branadic

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Re: new voltage reference from MAXIM
« Reply #6 on: June 13, 2016, 08:05:35 pm »
Wow, nice to see that they heard your prayer and  LT1027 is now available in LS8 package. I remember a mail conversion from 2012 with you Andreas, when you mentioned such a wish. So I guess you plan to do some comparision between LT1027xCH-5 and the new LT1027LS8?
Parameters are somewhat comparable to LT1027DCH-5, but at least a little bit different. I'm very interested in such results, as hermetic package version was not available for long time. How will they compare to LT1236LS8 and LTC6655LS8?
New input for you, I'm sure :)
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Online Andreas

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Re: new voltage reference from MAXIM
« Reply #7 on: June 13, 2016, 09:13:26 pm »
Hello,

unfortunately I do not have any old TO-5 hermetically LT1027.
And I guess that those you can buy nowadays are only fakes.

From my comparison measurements of DIP8 LT1027 against DIP8 LT1236/MSOP LTC6655
The LT1027 has the lowest hysteresis (typically < 1ppm over 25+/-15 deg C).
So if they did not change the chip layout I expect excellent stability for the LS8 package.
Perhaps even slightly better than my up to now favourate AD586LQ with the advantage that
the LT1027 can be operated at around 10V whereas the AD586 needs minimum 14V for proper stability.

But against the old TO-5 package there will be no mechanical decoupling from the PCB.
So the new parts are worse if not properly decoupled from PCB stress.

Does anyone have a chip foto / bondout layout from a old datasheet of the LT1027?
Or a defective LT1027**H for a photo. (I am shure branadic would do a photo if he gets one of those chips).

With best regards

Andreas
 
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Offline lowimpedance

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Re: new voltage reference from MAXIM
« Reply #8 on: June 13, 2016, 11:50:23 pm »
Does anyone have a chip foto / bondout layout from a old datasheet of the LT1027?

Had a look in a 1990 Prelim data and 1992 data book and there is no such detail unfortunately.
And seems all other components in the 'vintage paper' data books also do not include pictures of the die/bondouts.
The odd multimeter or 2 or 3 or 4...or........can't remember !.
 

Offline ebclr

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Re: new voltage reference from MAXIM
« Reply #9 on: June 14, 2016, 01:15:50 am »
What about LT6657

 

Offline necessaryevil

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Re: new voltage reference from MAXIM
« Reply #10 on: June 15, 2016, 08:38:35 pm »
Quote
If the heated chip is powered up during the temperature cycle, the die sees much less "delta T" during the cycle. The chip does indeed change the amount of power into the heater. That change *does* have an impact. It is much less than the impact of a cycle on an un-heated part. Indeed the ideal case would be a heated part inside a heated enclosure. That has it's problems as well ....
So, this means that hysteresis is more or less caused by temperature difference in the case and the die? Or, more accurate, caused by difference in expansion/shrinkage of the die and the case?
 

Online Andreas

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Re: new voltage reference from MAXIM
« Reply #11 on: June 15, 2016, 09:38:32 pm »
So, this means that hysteresis is more or less caused by temperature difference in the case and the die? Or, more accurate, caused by difference in expansion/shrinkage of the die and the case?

I blame it on the die attach (usually some kind of (filled) epoxy) which has
a elastic component which "remembers" tensions and stresses the die.
And of course the package if it is a plastic (epoxy) package.
But I also think that with a clever chip layout these effects could be minimized.

k=topic=69565.msg961475#msg961475 date=1465866950]
What about LT6657
[/quote]
No experiences with that part. (not in my focus because of plastic package).

With best regards

Andreas
 

Online Alex Nikitin

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Re: new voltage reference from MAXIM
« Reply #12 on: June 16, 2016, 07:51:39 am »
Any experience with this LT1021CMH supply?

http://www.ebay.co.uk/itm/191123710347?

I've bought a couple and plan to test these but right now I have very little "free" time to do it. It looks good however and the price is OK for a NOS metal case C grade reference.

Cheers

Alex
 

Online tszaboo

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Re: new voltage reference from MAXIM
« Reply #13 on: June 16, 2016, 08:36:48 am »

I received today a newsletter from MAXIM. Seems, they have a new voltage reference:


Hello,

if you really want a "new" (old) voltage reference you could try the brand new LT1027 in hermetically LS8 package.
http://www.linear.com/product/LT1027LS8

with best regards

Andreas
My only problem with the LT1027 is the tempco. I mean we get DACs with built in 2ppm/K references, the 5ppm/K of the LT1027 is not that impressive. Sure you get less moisture and aging, but the tempco ruins it.
I rather have a good tempco reference like the LTC6665.
 

Offline d-smes

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Re: new voltage reference from MAXIM
« Reply #14 on: June 16, 2016, 10:48:50 am »
I think it's the drastic up-curve above 100C that gives the LT1027LS8 the 5ppm/K tempco.  See "Output Voltage Temperature Drift" graph on page 4 of LT1027LS8 data sheet.  Stay within 10-20C of room temperature, and typical tempco curve is fairly flat.
 

Online tszaboo

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Re: new voltage reference from MAXIM
« Reply #15 on: June 16, 2016, 10:58:20 am »
I think it's the drastic up-curve above 100C that gives the LT1027LS8 the 5ppm/K tempco.  See "Output Voltage Temperature Drift" graph on page 4 of LT1027LS8 data sheet.  Stay within 10-20C of room temperature, and typical tempco curve is fairly flat.
Since they only give you the "box method" for some huge, usually -25 to 125 temperature range, the guaranteed drift is going to be more than the actual for a 20 to 30 celsius range. But that is the guaranteed spec. Unless there is a better number, or you can test enough units to build a confidence in it, I go with the datasheet numbers.
 

Online Alex Nikitin

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Re: new voltage reference from MAXIM
« Reply #16 on: June 16, 2016, 11:14:18 am »
My only problem with the LT1027 is the tempco. I mean we get DACs with built in 2ppm/K references, the 5ppm/K of the LT1027 is not that impressive. Sure you get less moisture and aging, but the tempco ruins it.
I rather have a good tempco reference like the LTC6665.

The tempco is measurable and if required can be compensated for. The ageing, humidity sensitivity and hysteresis are not predictable and not possible to compensate. What the point of a low tempco if your reference may drift considerably on it's own even at the same temperature? 

Cheers

Alex
 
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Online tszaboo

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Re: new voltage reference from MAXIM
« Reply #17 on: June 16, 2016, 11:43:24 am »
My only problem with the LT1027 is the tempco. I mean we get DACs with built in 2ppm/K references, the 5ppm/K of the LT1027 is not that impressive. Sure you get less moisture and aging, but the tempco ruins it.
I rather have a good tempco reference like the LTC6665.

The tempco is measurable and if required can be compensated for. The ageing, humidity sensitivity and hysteresis are not predictable and not possible to compensate. What the point of a low tempco if your reference may drift considerably on it's own even at the same temperature? 

Cheers

Alex
Have you ever tried compensating tempco? Please just describe how much effort it is to do that.
 

Online Alex Nikitin

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Re: new voltage reference from MAXIM
« Reply #18 on: June 16, 2016, 12:16:05 pm »
Have you ever tried compensating tempco? Please just describe how much effort it is to do that.

The easiest way is (as you probably aware) is a temperature stabilization. In a small range (say +/-10C) a parametric compensation is relatively simple. If you need the reference to work across the complete range of temperatures, than errors the tempco can introduce are comparable to the drift and hysteresis variation so a low tempco would be a good thing. But in that case we are talking about ~100 ppm errors.

Cheers

Alex
 

Offline branadic

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Re: new voltage reference from MAXIM
« Reply #19 on: June 16, 2016, 05:05:54 pm »
Quote
Have you ever tried compensating tempco? Please just describe how much effort it is to do that.

Well, Joe Geller did on his SVR-T:

"The -T option adds a 100 kilo ohm thermistor in series with a fixed temperature compensation gain resistor for a secondary temperature compensation scheme (developed by Lars Walenius, Sweden)."
Computers exist to solve problems that we wouldn't have without them. AI exists to answer questions, we wouldn't ask without it.
 

Offline acbern

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Re: new voltage reference from MAXIM
« Reply #20 on: June 16, 2016, 06:22:48 pm »
The problem with this is that it is very hard to predict behaviour too. How strong is thermal coupling between thermistor and referenc, what exactly is the compensation required, each reference requires manual adjustment as coefficients are varying...
So, does not replace a tempeature stabilized (oven) solution.
 

Online Andreas

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Re: new voltage reference from MAXIM
« Reply #21 on: June 16, 2016, 09:14:43 pm »
Have you ever tried compensating tempco? Please just describe how much effort it is to do that.

I do this for my 24 Bit battery powered ADCs.
I am using a 3rd order regression curve to compensate for the tempco of the voltage reference.
(The LTC2400 itself has a negligible TC).
The advantage against heating is a very low power consumption. (< 50mW against > 200 mW)
Of course you cannot use such a system together with large environment temperature gradients.
(But any precision instrument is not good at that).

Effort:
On the hardware side: only a cheap NTC + 1% pull up resistor on a 10 Bit (or better 12 Bit) ADC input.
For the adjustment: A automated temperature cycle for measuring the voltage reference (around 10-14 hrs machine time) to calculate a 3rd order regression curve.
The coefficients are stored within a controller which I need anyway to read out the ADC.

With best regards

Andreas
 

Offline uncle_bob

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Re: new voltage reference from MAXIM
« Reply #22 on: June 16, 2016, 09:29:47 pm »

Have you ever tried compensating tempco? Please just describe how much effort it is to do that.

Hi

Some fairly basic math:

You have a tempco of (say) 20 ppm.

It is measurable / repeatable / predictable to some percentage of that. Let's say 5%

Your math is perfect (it's a formula in a MCU).

Your temperature range is 100C (say -30 to +70)

So:

If you know the temperature to a repeatable 1 C, it is 5X better than you would need for a straight line correction. For a parabolic, you might want 2 or 3C. If you have 1C, it pretty much drops out.

Result would be a part that is compensated to ~1 ppm over a 100 C range.

For under a dollar, you can get a *bunch* of different solid state temp sensors. They have different accuracy ratings, but in general are all very repeatable and stable long term. Resolutions in the 0.06C range are not uncommon. Averaging will get you a bit better than that. Repeatability to 0.1 C is achievable with some care (don't mount the sensor next to the power regulator ...). They are highly linear and hold resolution over the entire range. A NTC plus resistor has great resolution at some central temperature. Not so much at the extremes.

We dumped NTC's almost a decade ago and switched to the solid state gizmos. From what I have seen, there is no reason at all to go back to the thermistors. Our math is about 10X tighter than what I've shown above. We do indeed average the output a bit.

Bob
 

Online Andreas

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Re: new voltage reference from MAXIM
« Reply #23 on: June 16, 2016, 09:36:35 pm »
Hello,

Just some measurement values of 2 samples of LTC6655B
(Typical TC 1 ppm/K max TC 2 ppm/K according to datasheet measurement method = 3 point box method)

ADC14 is built with a plastic MSOP8 package on a slotted PCB.
ADC20 is built with a hermetic LS8 package mounted dead bug style in a PCB cutout to avoid PCB stress.

in both cases around 180uV (=52ppm) measured output voltage change over 25-30 deg C temperature change giving around 6-7uV/deg C
corresponding nearly 2ppm/K with respect to the input voltage of 3430mV.

The plastic package shows +/-20 = 40uV or 12ppm hysteresis.
The LS8 hermetically package shows +/-14 = 28uV or 8 ppm hysteresis.

Red line: ADC output value in mV at constant input (LM399 reference divided by 2) over temperature.
Green line: 3rd order regression curve.
Blue line: resulting error in uV (mainly hysteresis of voltage reference with LTC6655)

With best regards

Andreas
 

Offline uncle_bob

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Re: new voltage reference from MAXIM
« Reply #24 on: June 16, 2016, 09:46:22 pm »
Hello,

Just some measurement values of 2 samples of LTC6655B
(Typical TC 1 ppm/K max TC 2 ppm/K according to datasheet measurement method = 3 point box method)

ADC14 is built with a plastic MSOP8 package on a slotted PCB.
ADC20 is built with a hermetic LS8 package mounted dead bug style in a PCB cutout to avoid PCB stress.

in both cases around 180uV (=52ppm) measured output voltage change over 25-30 deg C temperature change giving around 6-7uV/deg C
corresponding nearly 2ppm/K with respect to the input voltage of 3430mV.

The plastic package shows +/-20 = 40uV or 12ppm hysteresis.
The LS8 hermetically package shows +/-14 = 28uV or 8 ppm hysteresis.

Red line: ADC output value in mV at constant input (LM399 reference divided by 2) over temperature.
Green line: 3rd order regression curve.
Blue line: resulting error in uV (mainly hysteresis of voltage reference with LTC6655)

With best regards

Andreas

Hi

... and the next layer to the problem is that the hysteresis "goose egg" is a function both of rate of change of temperature and of the temperature range. Simply put: You can only just do so well and then it's not worth it to take all the data. No, this does not just apply to compensating voltage references. I can show you an *identical* plot (other than units) on ....errr .... something else. Of course if I did, I'd be fired, it's my employers data.

Bob
 


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