VRE305A - Page 1
Forum section: electronics / projects

author: fabioadriano
author_rank: Contributor
timestamp: November 04, 2016, 12:21:57 pm
content: Hi dears ! I was searching info about the subject IC and i find this forum ! GOOD !!!I've a simple question : i found on Aliexpress * this IC, the 'A' type ( e.g. initial error 5 mV & temp coeff = 0.6 ppm/°C !!)It has this cost : 7.1 $ (free shipping cost !!!)It seems too good !! (i've ordered two of these, just to see if its true !, fortunely i work here :https://www.inrim.it/enso i can MEASURE it with enough precision ...)BUT i also ask YOU : it seems TOO low this price ! It's possible ?Tnk you for your attention, my best regards.*https://www.aliexpress.com/item/Free-Shipping-1pcs-lot-VRE305A-VRE305/32699139603.html

author: Andreas
author_rank: Super Contributor
timestamp: November 04, 2016, 03:23:06 pm
content: Hellothe current price at digikey is a factor 10 higher than your source.Too cheap to be genuine.I hope you are able to measure a T.C. in the 0.6 ppm range.I recommend also to measure the noise (3uVpp) of the device.with best regardsAndreas

author: fabioadriano
author_rank: Contributor
timestamp: November 04, 2016, 03:50:52 pm
content: Hi, tnk you for your attention .... !!But, REALLY someone write on another chip this name ? (see the photo, when they arrive i look if its the same !).If your answer is YES i think that this persons have time & capacity to do this !!!!!!

author: Andreas
author_rank: Super Contributor
timestamp: November 04, 2016, 03:59:01 pm
content: Hello,I have here some MAX6350MJA in ceramic case which behave definitely like a cheaper REF02 reference.- noise- voltage at temperature pin...so yes some have the time and capabilities to package a cheap TL431 into a package that looks like a VRExxxwith best regardsAndreas

author: fabioadriano
author_rank: Contributor
timestamp: March 09, 2017, 11:12:09 am
content: It's arrived !!! I waited enough ...It seems USED & recovered from other circuit ( = peraphs this means that's NOT a 'made in China copy .... peraphs ...)in the second photo you see that ... the cover remained in my hands !! (good, so i can see HOW is made !!, i NEVER see an IC under the cover !!!)Now i stuck the cover on the IC ...Ok, in next days i try if it goes well !!!

author: amspire
author_rank: Super Contributor
timestamp: March 09, 2017, 11:46:07 am
content: Great photo, fabioadriano. I have been wanting to see the hybrid compensation network in one of these Thaler Corp reference chips.I knew there was an IC and a resistor/ntc compensation network, but it looks like temperature sensing diode, the buried zener and the FET current source for the zener are separate chips. Looks like at least 3 resistors in the calibration and compensation network hybrid have been laser trimmed. Trimming a temperature compensation network sounds like an expensive step.The temperature sensing diode has always been frustrating, because Thaler, Cirrus and now Apex have never once explained how it was wired and how it should be used. I now know it is just a grounded diode with a resistor to the + supply. So if you want to use it to accurately control the chip temperature, you have to make sure the chips + supply voltage is pretty stable.I will have to draw the full circuit out to add to my notes on the chips.I have a bunch of original parts plus some of the cheap used parts from China and one day I will get around to testing them.The cheap Chinese parts by the way are completely genuine, but if they have been overheated in the removal, they may be damaged. The used one that was tested in another post seemed to have more drift then the original part. The initial price of the Thaler VRE305A and the VRE310A was, from memory, about US$15 to $20. When Cirrus Logic bought them, the price went up overnight to something like US$70 and everybody stopped using them.Richard

author: fabioadriano
author_rank: Contributor
timestamp: March 09, 2017, 12:19:07 pm
content: Good Richard !! I see that you know this IC !!!So i ask you !I THINK that :n°1 is the IC (too easy this)n° 4 is the temperature sensor (easy 'cose i see that is connected to pin 3)n° 3 is FET ('cose i see it has 3 terminal & is connected also to pin 2 (+Vin) )n° 2 is the ZENER diode (i see its connected to FET ...)its correct ?

author: amspire
author_rank: Super Contributor
timestamp: March 09, 2017, 12:40:57 pm
content: Just did a quick measurement on my VRE305A and VRE310A.If you choose the 100K range on the DMM, you can measure a couple of the thick film resistors. The thing is if you know this resistor, you can work out every other thick film resistor based on their geometry.Rd is the diode going to the temp sense zener - measure between pins 2 and 3R2 is the resistor across the opamp input from the zener - measure between pins 7 and 8Unused VRE305A Rd and R2: 13K0,12K1 ; 13K1, 12K4 ; 12K8, 12K0 ; 13K4, 11K7Used VRE305A Rd and R2: 12K8, 12K0 ; 12K9, 12K0 ; 14K8, 13K4Used VRE310C Rd and R2: 11K9, 20K9 ; 11K7, 20K0 ; 17K3, 30K9The concern with these numbers is one of the used VRE305As and one of the VRE310C were a long way out. This could be a sign of damage.These two tests may be a quick test to sort out which IC's may have been damaged.The other alternative is that they change the thick film resistance to match the characteristics of the zener. So they batch the zeners according to zero temp coefficient current, and then vary the thick film resistor thickness to adjust for each batch of the zeners.All my unused VRE305As are probably from the same batch.

author: amspire
author_rank: Super Contributor
timestamp: March 09, 2017, 12:43:03 pm
content: Quote from: fabioadriano on March 09, 2017, 12:19:07 pmCompletely correct. The black printed shapes are the resistors. The grey ones are NTC thermistors.It is likely that the opamp is manufactured by another company. If you can zoom in more, it may be possible to get a clue about the opamp type.

author: fabioadriano
author_rank: Contributor
timestamp: March 09, 2017, 01:24:01 pm
content: Right ! Thnk you for your answer !p.s. i try to measure R from (pin 2 to pin 3) & from (pin 7 to pin 8 ), these are the values of the two IC that i buy from Aliexpress :1) 18.105 / 8.810 KOhm2) 18.737 / 13.342 KOhm.. reading on the ics they seems born in the same date .... in next days i try to MEASURE they !!!

author: amspire
author_rank: Super Contributor
timestamp: March 09, 2017, 01:42:17 pm
content: Quote from: fabioadriano on March 09, 2017, 01:24:01 pmThat is a lot of digits of resolution. You want to test at less then 0.1V so you want to be on a high range - like a 399K range or a 599K range. Don't let the meter autorange.A quick test - if you get a different reading when you reverse the leads, you need to go to a higher range.

author: fabioadriano
author_rank: Contributor
timestamp: March 09, 2017, 01:59:49 pm
content: OK, now i put the range = 1M but the reading is the same (i also set 100k and there is no change). Nothing change also if i reverse polarity of the probes.ex. this is from pin 2 & 3 of IC2

author: Andreas
author_rank: Super Contributor
timestamp: March 09, 2017, 02:25:17 pm
content: Quote from: fabioadriano on March 09, 2017, 11:12:09 amHello,Thanks for opening.but now its "kaputt"I never thougth they use thick film resistors for the price they take.I had expected laser trimmed thin film resistors instead.Perhaps that explains the high noise level that I had on two similar VRE3050A devices.with best regardsAndreas

author: fabioadriano
author_rank: Contributor
timestamp: March 09, 2017, 02:37:46 pm
content: hi Andreas, NICE to read you !!1) i didn't open it .... = the cover of one of the two ic was ALREADY detached2) can you explain, with simple word please, why it's OFF ? (i prefer to use this word ...)3) i remember that you wrote me that "at these price the IC is not genuine" so, when you write "they use" you mean Chineses or Thaler corp ?best regards

author: amspire
author_rank: Super Contributor
timestamp: March 09, 2017, 03:23:11 pm
content: Quote from: fabioadriano on March 09, 2017, 01:59:49 pmI have drawn out the circuit with resistor values. I will tidy it up tomorrow and post it.First - something that surprised me, not all the resistors are printed with the same compound. At least one resistor is printed with material that has 100 times the resistance of the other resistors - this is the one at the bottom with the rounded ends that goes to the trim pin. It is about 1.5MBytes.What I worked out is that the two resistors Rd and R2 are both trimmed, so they will vary. If you power it up and the voltage is right, then the values are probably right.The big fat 3K7 resistor above the zener is actually completely cut through, so that will be there just for the calibration trimming process. When it is in the circuit, it take the voltage to the opamp from the zener down below 2V. I suspect it is part of the process for optimizing the zener current for minimum drift. It probably lets them measure the zener temperature drift at two slightly different currents and from that they can calculate the voltage on pin 8 that is needed following the trimming for minimal temp coefficient in the zener.Andreas is correct in that the IC without the top is probably done for. The chip needs a hermetic seal, and it is now likely to be contaminated. Any attempt to glue the top back on will contaminate it some more.But we will probably end up knowing way more about the family of references then we ever did from the lousy data sheet. For a devices claiming some of the best specifications in the industry, they should have more information and application notes.The data sheet always contained some fantastic specifications, but the values of the parts worries me a bit. The 6.3V is probably divided down to 3.4V and it is then amplified up to 5V again. Now about 2% of this feedback for the amplifier consists of 4 thermistors and 4 resistors making up the compensation network. So if you are hoping for drift in the ppm, you are relying on the effect of these 8 parts to be a drift around 1 part in 20,000.I guess I will find out when I test my parts. See if they are all still within 0.01% of each other for a start.

author: fabioadriano
author_rank: Contributor
timestamp: March 09, 2017, 03:59:57 pm
content: Good !!! NICE news ! I wait other news !!!about the crash of my IC, it's not a problem, i will try anyway to see if it goes ! (and in what way ...)Tnk you again for your attention.(p.s. what is 'bad' toward chip surface ? Air ? Dust ? Light ? , i ask these 'cose fortunely our workshops are 'dust free', thermostated & so on ... )

author: Andreas
author_rank: Super Contributor
timestamp: March 09, 2017, 04:59:19 pm
content: Quote from: fabioadriano on March 09, 2017, 02:37:46 pmHello,2) a reliable hermetical sealing needs to be done by glass with same CTE than the other materials. (ceramic, KOVAR pins)Otherwise humidity will degrade the parts (resistors) by oxidation. -> faster ageing drift.3) good question. I was assuming that its genuine. But on the other side a well treated genuine part should not lift its "hat" that easily.Looking forward to your T.C. measurements and noise measurements.Current consumption against data sheet would be also interesting.My two VRE3050A devices from DigiKey had a too low current consumption.(data sheet typ. 5 mA, actual ~2 mA)With best regardsAndreas

author: fabioadriano
author_rank: Contributor
timestamp: March 10, 2017, 02:50:59 pm
content: ok, first speedy measures :Vsupply = 15V1st IC : (the 'open' one) ... KOIsupply = 1.92 mAMeas. value :2.9728651 VAfter 1 hour of supply, i read in about 30 minstd dev. = 1.124 e-3!!!! (with about 1000 readings values ... ) = wrong & unstable ....2nd IC : OK !Isupply = 4.43 mAMeas. value :5.0007004 VAfter 1 hour of supply, i read in about 30 minstd dev. = 26.611906 e-6(with about 3000 readings values ... )in next days i will look better the OK ic ....

author: amspire
author_rank: Super Contributor
timestamp: March 10, 2017, 03:18:49 pm
content: With that first 2.97V device, if the voltage on pin 8 is almost the same as the output, then you have a broken connection in the opamp divider chain to ground.With the second, it could be the reference is drifting or it could be the meter is drifting.There are two ground pins - pin 4 and pin 7. If you are using pin 4 as the power supply ground, are you using pin 7 as the reference output ground? So you should be measuring between pins 6 and 7?Richard

author: fabioadriano
author_rank: Contributor
timestamp: March 10, 2017, 03:47:11 pm
content: right, next time i measure output in pins 6 & 7. (for these measures i read output in pin 6 & 4 , cose i read on the datasheet that"The VRE305 reference has the ground terminal brought out on two pins (pin 4 and pin 7) which are connected together internally"... so i think this kind of "light measures" will be the same ....