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.
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.
I received today a newsletter from MAXIM. Seems, they have a new voltage reference:
Does anyone have a chip foto / bondout layout from a old datasheet of the LT1027?
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?
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
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.
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.
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.
Have you ever tried compensating tempco? Please just describe how much effort it is to do that.
Have you ever tried compensating tempco? Please just describe how much effort it is to do that.
Have you ever tried compensating tempco? Please just describe how much effort it is to do that.
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