5V precision referene - Page 1
Forum section: electronics / general

author: kcs
author_rank: Regular Contributor
timestamp: January 06, 2013, 02:35:46 am
content: I want to build a simple yet relatively precise 5V reference. I have searched DigiKey for suitable IC and found some that could fit my needs. Is ADR4550BRZ a good choice fromthis list? Seems to be a good value for money, but maybe I am missing something?Another question: how should I protect this IC from ESD?

author: ttp
author_rank: Regular Contributor
timestamp: January 06, 2013, 05:25:23 am
content: Voltagestandard.com (http://www.voltagestandard.com/DMMCheck.html) use TI REF5050, another candidate.

author: kcs
author_rank: Regular Contributor
timestamp: January 06, 2013, 06:54:11 am
content: REF5050 is in that list. It costs about the same but has a slightly worse characteristics. I am wondering why they have decided to go with REF5050. It is also interesting how they manage to assure 0.01% accuracy when max accuracy for this IC, based on datasheet, is 0.05%.I have found thatwww.voltagestandard.comis offering Vref5-002, a 5.000V, 0.0025% accurate precision voltage reference device. They use VRE305A as a main chip. It looks impressive on datasheet, but it costs $93 on DigiKey. I can get it for under $30 from eBay but I am not sure whether it is some sort of scam or not.Too many choices...

author: thmjpr
author_rank: Regular Contributor
timestamp: January 06, 2013, 08:51:18 am
content: Quote from: kcs on January 06, 2013, 06:54:11 amNote the datasheet value is tolerance for initial value when it starts being used. If your design is to drop in the part, then yes you will expect 0.05%. However if you plan to calibrate your circuit the initial value is not important (within reason). It's OK if its out by 10%, because you can use your3458A(capable of <0.001% accuracy) to measure it and adjust/record appropriately. You have a calibrated 3458A right?Then the important part after calibration is stability + temperature coefficient. Dave has mentioned this in some videos.Quick comparison:ADR4550BRZ0.02%, 2.0 ppm/°C, 25ppm/1khrsMAX6250ACSA0.02%, 2.0 ppm/°C, 20ppm/1khrsREF5050IDGKT0.05%, 3.0 ppm/°C, 50ppm/1khrsI personally would not use the ebay part unless you have access suitable equipment to check at least initial accuracy.

author: aghp
author_rank: Regular Contributor
timestamp: January 06, 2013, 10:27:00 am
content: With this, it is also quite easy to make good 5VTI REF102C5ppm/khr typ2.5ppm/Celsius.(but look datasheets more deep and you can see there are temp areas where it is nearly zero, I have used this for my "transfer standard" where pre aged and temperature shoked Ref102C is ovenized to 42 celsius with extremely tight temperature control an dwith good thermal insulation. But this is only one my own "volt-nut"experiment . I have developed improved version using around 30 parallel "averaged" (noise reduction) Ref102 but this experiment is not ready due to difficulties with low frequency noise handling... 0.01Hz to 10Hz area and it IS difficult to reduce this noise residues. There in this experiment can also easy find that example 20 mm long thick copper wire is too high value resistor and then also knock head to "big" thermal voltage problems). It is more easy (and cheaper) to buy ready made Fluke transfer reference but experiment is good way to learn...least that it need respect HP and Fluke and Keithley higher end items etc.))

author: Fox
author_rank: Regular Contributor
timestamp: January 06, 2013, 02:52:39 pm
content: The folowing ones would be good choices (also the Analog Devices one you mentioned)LTC6655B 0.025%, 2ppm/°C max and 1ppm/°C typicalorISL21009 0.01% 3ppm/°CIt depend how do you want to use it, if want to use batteries to power the reference i would recommend the ISL21009 or the ADR4550.If you want low noise performace the LTC6655 is the one to go.Altough the MAX6250 and the REF5050 are good references too.As for ESD protection the LTC6655 has internal protection diodes and the ISL21009 is rated up to 6kV (Human Body Model), so you don't necessarilyneed external ESD protection.If you haven't already i would recommend reading the Appnote AN82 from Linear Technology "Understanding and applying Voltage References" andDesign Note DN229 "Don't be fooled by Voltage Reference Long-Therm Drift and Hysteresis" also from Linear Technology

author: kcs
author_rank: Regular Contributor
timestamp: January 06, 2013, 06:14:41 pm
content: Quote from: aghp on January 06, 2013, 10:27:00 am5ppm is only for REF102CM (TO-99) which is obsolete and hard to get. For other packages it is 20 ppm. REF102 outputs 10V and requires expensive INA105 to get 5V.It seems that HP 3458A usesLTZ1000for reference voltage. Typ =7.2V, Min=7.0V, Max=7.5V. Is that precision?I have made a comparison table of some reference ICs. Based on my findings, I believe I will go with MAX6250ACSA+. It seems to the best value for money.

author: Bored@Work
author_rank: Super Contributor
timestamp: January 06, 2013, 06:29:43 pm
content: Quote from: kcs on January 06, 2013, 06:14:41 pmThe absolute value doesn't matter. It is supposed to be calibrated. What matters is short and long-term drift, including tempco. And there that reference shines.

author: Neganur
author_rank: Unknown
timestamp: January 06, 2013, 09:01:30 pm
content: Quote from: kcs on January 06, 2013, 06:14:41 pmCompare its tempco to the ones in your table0.05ppm/°C

author: kcs
author_rank: Regular Contributor
timestamp: January 06, 2013, 09:31:56 pm
content: Quote from: Neganur on January 06, 2013, 09:01:30 pmYeah, really not bad for $50.

author: nukie
author_rank: Frequent Contributor
timestamp: January 06, 2013, 11:43:40 pm
content: LTZ1000 is as good as it can get and it is proven to work well in one of the best multimeter.I have three sets of reference built around the LTZ1000 and LT1013 burn in and aged for two years. Readings taken from the lab, I couldn't read any drift with the Keithley 2000. I don't power it all the time, I just hook it jobs warm up for 2 hours before I take readings. Drift is too small for any 6 1/2 digit multimeter.So maybe you might want more challenge building a 7v reference.

author: Unknown
author_rank: Unknown
timestamp: January 07, 2013, 12:04:34 am
content: The LTZ1000 is also used in commercial voltage references (eg. Fluke 732B). They key to precision references is usually the word 'selected'. Fluke and Agilent burn in the references for many hours and choose the one with the best drift/noise/tempco characteristics.As was already stated multiple times in this thread, you should value stability over initial accuracy. You can measure a stable reference once and it will hold this value for years. A reference with good initial accuracy put poor tempco/drift will require much more frequent calibration, so what's the point of the initial accuracy?

author: Hypernova
author_rank: Unknown
timestamp: January 07, 2013, 01:22:19 am
content: Is there any study how how long a reference will age for, theses things are like wine but is there a point where they stop drifting in a practical sense?

author: Unknown
author_rank: Unknown
timestamp: January 07, 2013, 02:07:17 am
content: It will depend on the reference, some might never stop drifting. Agilent, Fluke and Keithley will have tons of data on the aging of the references they use (eg. LM399, LTZ1000), but I doubt that they ever published any of it.Inthis article by Bob Peasehe mentionts a testing program where they age LM199 references for six weeks. Note that this was only to select them. The LM199 runs at 85°C, not sure what this means for how fast the aging plateaus (high temperature will increase aging, but may also allow it to reach a plateau sooner). Some manufacturers specify a much lower aging rate after the first 1000h of operation, but this data may be based on accelerated life time studies (see the LT note that someone posted about what's wrong with that). Good references get much more stable over time, this is why many of those old bench DMMs are still in spec many years after their last calibration.Their is a graph in the LT LM399 datasheet which indicates that the aging slows down after 4 months. LT DN229 also shows some data for much shorter time scales. I'm not sure how applicable this information is for other references, but a time scale in the order of months seems to be a reasonable estimate. Note that aging will just slow down, it won't stop completely.

author: kcs
author_rank: Regular Contributor
timestamp: January 07, 2013, 03:16:41 am
content: I have understood that when you care about precision voltage reference you should be mainly interested in short and long period voltage shifts. Here are some of my thoughts:First. There are different levels of precision, eg. 5.000V and 5.000000V. I don't aim for the latter one.Second.VRE3050 datasheetsays that "Output Voltage: +4.9995 (Min), +5.0000 (Typ), +5.0005 (Max)". Correct me if I am wrong, but I understand that no matter what (even if temperature during measurement is -40°C or +85°C; or IC is turned on for 1 min or 1M hours) it should never output voltage above 5.0005 or below 4.9995. For example, LTZ1000 is not good for my needs because it could output 7.123456789V and this value could be very stable but I don't have accurate enough device to get this reading. So I will never know that mine LTZ1000 outputs 7.123456789V. And no, finding a company or a person who can do that precise measurement is not a option in my case.Interesting observation. Some manufacturers use "Output Voltage" statement and some use "Initial Output Voltage". As I understand, the first should guarantee that output will not exceed declared values no matter what.

author: Unknown
author_rank: Unknown
timestamp: January 07, 2013, 06:46:19 am
content: Output voltage for that device is specified for T=25C, not over the temp range. Note that the blurb on the first page talks about initial accuracy. Maybe I missed it, but what's wrong with the Geller labs and Voltagestandard products? You pay them the extra money to calibrate the reference with an expensive DMM.

author: kcs
author_rank: Regular Contributor
timestamp: January 07, 2013, 09:56:57 am
content: Ok, you got me with T=25C. But it does not say anything about long-term stability. So at 25C over 10 years of continuous use output voltage should be within 4.9995-5.0005 range. No?There is nothing wrong with Geller labs and Voltagestandard products, I just originally wanted to do it myself.

author: poodyp
author_rank: Regular Contributor
timestamp: January 07, 2013, 11:36:15 am
content: Quote from: kcs on January 07, 2013, 09:56:57 amIt says long term stability is 6ppm/1000hrs. After 10 years itcouldbe off worst case by 525ppm, or ±2.625mV, but you'll never know.

author: LaurenceW
author_rank: Frequent Contributor
timestamp: January 07, 2013, 01:33:03 pm
content: KCS, you state you want "easy" and "relatively precise", but I guess it depends on the degree of those terms!I have used a couple of MAX6225 devices, and right out of the box WITHOUT any adjustment, each gave 2.5000V on my 50,000 count Fluke 289. (5V devices also available). I cannot get them to budge from this figure over a reasonable range of temperatures or durations, so suspect that these devices (and maybe others) already perform much better that the spec sheets, and certainly good enough for my application.One thing, however. Make sure you stick to the spec sheets in terms of input and output capacitive decoupling, and take the voltage reference close to the pins of the device. Otherwise, you start to gain or lose even fractions of a mV in the voltage drop in your current-carrying circuit tracks/wires.I got my devices FREE from Maxim, who will supply engineering samples. You have to give them some reasonable expectation that you might buy more of their devices in the future! I said I was a designer (well, I am and do).

author: free_electron
author_rank: Super Contributor
timestamp: April 07, 2013, 11:48:20 pm
content: Quote from: alm on January 07, 2013, 12:04:34 amNo it is not !. i got proof !. keep your eyes peeled....

author: amspire
author_rank: Super Contributor
timestamp: April 08, 2013, 12:33:13 am
content: Quote from: free_electron on April 07, 2013, 11:48:20 pmInteresting - just had a peek at the manual. There is hope for us all.Teardown photos would be really interesting particularly on how they have built the oven.I love the spec that says if the reference has been off for over 1 hour, you have to turn it on for 24 hours to settle.

author: free_electron
author_rank: Super Contributor
timestamp: April 08, 2013, 12:36:16 am
content: and that is what i got ... It was time to replace the battery so i tore it completely down

author: fmaimon
author_rank: Unknown
timestamp: April 08, 2013, 12:46:24 am
content: Not needed anymore --> If you want to wait for free_electron's teardown, don't try to read the spoiler below...From the schematic on page 4-6 (60) of the 732B datasheet I would say that it uses the SZA263 / LTFLU-1, as it is the only reference I know that has this kind of connection...

author: amspire
author_rank: Super Contributor
timestamp: April 08, 2013, 01:15:56 am
content: Quote from: fmaimon on April 08, 2013, 12:46:24 amLooks like you are right. Is there any data anywhere for the SZA263?

author: free_electron
author_rank: Super Contributor
timestamp: April 08, 2013, 01:31:06 am
content: LTFLU-1 In mine combined with op97 to make 10 volt

author: Unknown
author_rank: Unknown
timestamp: April 08, 2013, 09:24:40 am
content: Quote from: free_electron on April 07, 2013, 11:48:20 pmPlease check your sources before declaring a post false four months later. The Fluke 732A and early 732B models used a Motorola reference, and the later Fluke 732B models used the LTZ 1000 (obviously a highly selected and burned in version).Hereis a document from someone who might know a thing or two about Fluke voltage references that supports this.

author: fmaimon
author_rank: Unknown
timestamp: April 08, 2013, 09:35:32 am
content: I can't find any datasheet on it, but this guy has some info:http://www.eefocus.com/lymexbg2vo/blog/10-01/183124_69352.htmlIt's in chinese, so google translate to the rescue:http://translate.google.com/translate?hl=en&sl=auto&tl=en&u=http%3A%2F%2Fwww.eefocus.com%2Flymexbg2vo%2Fblog%2F10-01%2F183124_69352.html

author: Dr. Frank
author_rank: Super Contributor
timestamp: April 08, 2013, 10:38:49 am
content: Quote from: alm on April 08, 2013, 09:24:40 amSorry alm,Fluke never used the LTZ1000 in any of their own designed calibrators or references.Fluke always has used custom specific 'Reference Amplifiers' like the Motorola SZA263 or its (exact) replacement "LTFLU", from Linear Technology.Their characteristic is, that the zener diode is connected to the emitter of the transistor in the same package.That special Fluke reference schematic was already used for the very early calibrators, as 332B, 335B/D, where an equivalent TI Reference was used. The advantage is, that you can amplify the ~ 7V volt of the Reference amplifier directly to 10,000V with the same OpAmp.In the article from Deaver, a "Linear Technology Reference" is mentioned, but that's simply the "LT-FLU".Reason for that change is the Part Termination of Motorolas SZA 263. See the 732B teardown of free_electron.Deaver nowhere mentions explicitly an LTZ1000 like type.The use of the LTZ1000 instead of the SZA263 would have implied a complete redesign of the 732B, because the LTZ1000 is not compatible at all with the overall Fluke reference schematic.Only when Fluke acquired Metron Designs Ltd., and the 7001 reference, invented by famous John R. Pickering, it was the first LTZ1000 based reference with the brand of Fluke on it.Btw.: Fluke just terminated the 7001 reference system.That's a pity, because obvioulsy no big oven and no steady powering was required for those devices.Frank

author: amyk
author_rank: Super Contributor
timestamp: April 08, 2013, 10:56:10 am
content: Quote from: fmaimon on April 08, 2013, 09:35:32 amThere's a bunch more infoheretoo, also in Chinese.(Any idea why the Chinese seem to know so much more about these references? Maybethey get a lot of "scrapped" but working equipment sent there for disposal...)

author: Neganur
author_rank: Unknown
timestamp: April 08, 2013, 11:18:47 am
content: Quote from: amyk on April 08, 2013, 10:56:10 amWithout having too much of an idea about how people live their lives in either regions, the sheer amount of people*in China lets me imagine, that there also are more people who are interested in electronics.*: world population 7x109(2011), USA 0.32x109(2012), Europe 0.74x109(2012), China 1.344x109(2011)

author: Unknown
author_rank: Unknown
timestamp: April 08, 2013, 12:04:39 pm
content: Quote from: Dr. Frank on April 08, 2013, 10:38:49 amYou appear to be correct, I must have been confused with the later 7000 series that they acquired through Wavetek. I couldn't find any authoritative source for the reference used in the 732B (although I did find a bunch of non-authoritative volt-nuts posts claiming it is the LTZ1000), but the schematic clearly shows a zener diode connected to the emitter of a transistor, unlike the LTZ1000.

author: amspire
author_rank: Super Contributor
timestamp: April 08, 2013, 01:47:43 pm
content: Quote from: fmaimon on April 08, 2013, 09:35:32 amThis page and the pages it links to are really great. Thanks.Even has information about the LTFLU ic.Temp Stability: 5ppm/C0.3 ppm/ 1000 hours1ppm / yearRMS noise: 0.06 ppmThe 5ppm may not look that great but that would be an average coefficient over a range of temperatures. You can adjust the temperature coefficient by adjusting the zener current, so Fluke can get better then that .Once it is put in an oven that regulates to perhaps 0.01 degC, and you adjust the current to zero temp coefficient at the oven temperature, the end result could easily be below 0.01ppm/C.The thing about adjusting the zener current for zero temp coefficient is it is hard to adjust for zero temp coefficient over a range of temperatures, but you can precisely adjust for zero temp coefficient at one precise temperature.

author: nukie
author_rank: Frequent Contributor
timestamp: April 09, 2013, 12:03:41 am
content: Its very sad that we have to reference a Chinese website for an American made item. That's just show where the future of engineering is heading. I was very frustrated when I first started off studying precision voltage reference, the lack of information in the western. Without this Chinese 'nut' we would have lost great wealth of information.

author: amspire
author_rank: Super Contributor
timestamp: April 09, 2013, 12:59:08 am
content: What seems to be clear is that making great buried zener references is still as hard as ever, and IC companies would prefer not to know about it.It wouldn't surprise me if it comes down to trail and error tweaking - make a wafer. Test the devices. Tweak the parameters a bit and make another wafer. Continue until you have reached the correct performance.My guess is we will continue to see an improvement in other reference technology - like bandgap references - until they get good enough for secondary references. There is no incentive to even try and make better zener references.If a compact way can be invented to cool an IC substrate down to 4 deg K, then companies like Fluke may start using Josephson Junction references instead of zener-based references. Is there a lower temperature limit for the Peltier/Seebeck effect?

author: ecat
author_rank: Frequent Contributor
timestamp: April 09, 2013, 09:51:32 am
content: I don't know if there is a theoretical limit to commercial Peltier devices but iirc there is a practical limit in that the efficiency is inversely proportional to the temperature difference between the hot and cold sides of the device. So a delta T of 300degC requires either a massively powerful device (?) or a hideously inefficient stack of ever more powerful devices.That new fangled laser cooling looks interesting but I have no details.

author: Dr. Frank
author_rank: Super Contributor
timestamp: April 09, 2013, 01:29:52 pm
content: Quote from: amspire on April 09, 2013, 12:59:08 amNope, Bandgap references will never beat Buried Zener devices regarding long term stability:The Buried Zener structure is diffused deeply and safely below the surface and occupies a relatively big volume / area in the chip. Therefore, the diffusion and decay processes in the silicon crystal (depending basically on temperature, Arrhenius law) do not lead to such high drift rates over time, compared to the bandgap structures, latter ones being relatively small and situated vulnerable at the surface of the chip.2nd reason: Oxygen and humidity do not deteriorate the active silicon structure of the Buried Zener Devices, because of their hermetically sealed package.The ageing behaviour of Buried Zener devices can also not be improved significantly by a better design, because the dominating decay process in silicon follows a natural law.Only if bandgap references are ovenized, like buried zener devices, they may reach the same low T.C.That can not be achieved by better trimming of the bandgap refs, due to yield problems and quick worsening of trimmed T.C. over time due to above described deterioration of the chips structure.QuoteSorry, that will not happen:JJ arrays consist of Superconductors (e.g. Niobium structures), and can definitely not be made from silicon technology.Commercially available JJ arrays are produced by NIST, PTB and some specialized university institutes or one or two private companies only.You definitely need liquid Helium(4) to achieve 4.2K. No cooling element can do that.Even if you would construct a miniature Helium liquefier, you also would need a Helium dewar enclosure to set up your experiment.It's much easier to simply rent a dewar can filled with 50l of liquid Helium and dip your experiment inside.That all is already commercially available; complete metrology standards based on a JJ array @ 4.2K cost around 200k. (Fluke owns several of them)Recently, physicists demonstrated, that High Tc Superconductors (from YBaCuO) can be structured to make a JJ, and to get around 10^-8 uncertainty for the 'Josephson-Volt', at ~60K (pumped liquid nitrogen). That would be much easier regarding the low temperatures, but the YBCO - JJ is still far away from being available and affordable.Frank

author: amspire
author_rank: Super Contributor
timestamp: April 09, 2013, 01:31:03 pm
content: Quote from: ecat on April 09, 2013, 09:51:32 amIt would have to be a stack, but at the inner level, you could be looking at cooling a chip a small as 1mm square. Each device has to be two or three times the power of the previous device and probably six or more layers would be needed. I did a quick search. The current commercial Peltier devices cannot get down to 100K, but I did see a patent for a barium copper oxide superconductor Peltier device that can cool to a stable 65K. I know, it is a long way from 65K to 4K, but they are gradually getting closer. There has been a lot of work on high temperature Josephson Junctions for computers, and even back in 1995, they had junctions that worked up to 70K. So perhaps it is possible.I think the laser cooling you mentioned is only good for cooling Helium gas that is already extremely cold to start with.

author: amspire
author_rank: Super Contributor
timestamp: April 09, 2013, 01:48:01 pm
content: Quote from: Dr. Frank on April 09, 2013, 01:29:52 pmAgreed. I was never considering using silicon for a Josephson Junction.QuoteThat is just about in the range of Peltier cooling, and so that is promising. Of course devices built in a lab will be uncommercial, but once they know how to make these high temperature junctions, they will be much cheaper. The main motivation for development of high temperature Josephson Junctions is computing and very high frequency processing. When developed commercially, you will be down to fractions of a cent per junction.So combine a 70K high temp junction array with an achievable Peltier cooling down to 65K and problem solved!I know, it is easy to say.Richard.

author: branadic
author_rank: Super Contributor
timestamp: April 09, 2013, 08:20:30 pm
content: What about LT1236LS8?

author: casinada
author_rank: Frequent Contributor
timestamp: April 12, 2013, 04:47:19 am
content: There is some new competition to the Pentaref from voltagestandard.comI wonder if anybody got any of these:http://www.ebay.com/itm/New-AD584LH-4-Channel-2-5v-7-5v-5v-10v-High-Precision-Voltage-Reference-Module-/221210908532?pt=LH_DefaultDomain_0&hash=item3381329774http://www.ebay.com/itm/NEW-AD584LH-4-Channel-2-5v-7-5v-5v-10v-High-Precision-Voltage-Reference-Module-/221208115533?pt=LH_DefaultDomain_0&hash=item338107f94dA search on Taobao found:http://item.taobao.com/item.htm?spm=a230r.1.14.20.ZEFK2r&id=1255376596975Y = $12 US dollarsI don't know if they come with a certificate of calibration.

author: bingo600
author_rank: Super Contributor
timestamp: April 12, 2013, 07:17:18 am
content: Quote from: casinada on April 12, 2013, 04:47:19 amI'd not trust it ...Just the fact thait it switches the 3 voltages automatically to the plugs via a MCU , would make me want to see the the circuitI'll keep on trusting my Geller 10v/Bingo

author: ecat
author_rank: Frequent Contributor
timestamp: April 12, 2013, 11:46:35 am
content: Quote from: casinada on April 12, 2013, 04:47:19 amNo calibration that I can see, so just an out the box AD584 with 10V +/-5mV specs (assuming it is the L version) sitting right beside a boost converter.