LM399AH#PBF - Low stock worldwide - I need qty=30 - Page 1
Forum section: electronics / general

author: IanJ
author_rank: Unknown
timestamp: August 06, 2020, 07:04:43 pm
content: Hi all,Anyone got a bunch of LM399AH#PBF for sale.......stocks are low worldwide and I could do with 30 at least asap. Digikey are saying 16 weeks, same on Analog Devices website.According to Octopart, LTL Group have qty=2913 and i have emailed them.....but having never used them I don't know how reliable etc.Ian.

author: Kleinstein
author_rank: Super Contributor
timestamp: August 06, 2020, 07:21:14 pm
content: Mouser in Germany still show some 550 pieces in stock, and few more of the non A version.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: August 06, 2020, 07:25:57 pm
content: Ian,I am not sure I get mixed information from my searching:From LTL website I get:[ Specified attachment is not available ]From Google Maps I get:This doesn't look promising at all.But I also get:You can read the rest here:https://www.dnb.com/business-directory/company-profiles.leading_testing_laboratories_llc.27a169c3c6a47fffdc88c334f7cf3c7b.htmlRegards,Jay_Diddy_B

author: wraper
author_rank: Unknown
timestamp: August 06, 2020, 07:26:15 pm
content: Quote from: Kleinstein on August 06, 2020, 07:21:14 pmThey are not in stock. Expected around December.

author: razvan784
author_rank: Regular Contributor
timestamp: August 06, 2020, 08:19:27 pm
content: Why not buy some LM399H and maybe sort through them?

author: IanJ
author_rank: Unknown
timestamp: August 06, 2020, 09:08:24 pm
content: LTL are suggested on Octopart......does that mean vetted?

author: Andreas
author_rank: Super Contributor
timestamp: August 06, 2020, 09:28:33 pm
content: Quote from: razvan784 on August 06, 2020, 08:19:27 pmHello,I do not think that there is a large difference between A and non A type when being used near room temperature.It is more a issue when they are being used at the temperature extremes.with best regardsAndreas

author: IanJ
author_rank: Unknown
timestamp: August 06, 2020, 09:30:35 pm
content: Hi allStupid question......usually part number I buy is LM399AH#PBFWhats the #PBF part, lots of sites have it. Scared I get sent without thermal shield......Touchstone-sys.com per Octopart said they can get me 50off $21usd.....2-3 days.Ian.

author: wraper
author_rank: Unknown
timestamp: August 06, 2020, 09:31:54 pm
content: Quote from: IanJ on August 06, 2020, 09:30:35 pmLead-free

author: martinr33
author_rank: Frequent Contributor
timestamp: August 06, 2020, 09:44:37 pm
content: Might try these folks.https://bristolelectronics.com/lm399ah-linear-tech?___SID=U

author: IanJ
author_rank: Unknown
timestamp: August 06, 2020, 09:54:39 pm
content: Quote from: martinr33 on August 06, 2020, 09:44:37 pmThanks......have you used them?

author: IanJ
author_rank: Unknown
timestamp: August 06, 2020, 09:59:28 pm
content: Another question as I contemplate buying from companies I have never used or heard of.......is the LM399AH always sold with the thermal shield.......would hate to receive without.Ian.

author: IanJ
author_rank: Unknown
timestamp: August 07, 2020, 11:15:24 am
content: Hi all,Melinda Berry, Touchstone Systems per the link at Octopart says they have available. This seller appears to be legit as there are one or two reviews etc. Hmmmmmm!Was also wondering.......are there fake LM399AH's going around.....I ask because there are sellers from China selling on Ebay £4.66 ($6.12) each.Ian.

author: wraper
author_rank: Unknown
timestamp: August 07, 2020, 11:52:34 am
content: Quote from: IanJ on August 07, 2020, 11:15:24 amMany of them may be LM399H remarked as LM399AH. Also many of them are salvaged ICs with new iron legs welded on top of kovar to make them look new.

author: The Soulman
author_rank: Super Contributor
timestamp: August 07, 2020, 01:20:01 pm
content: Quote from: Kleinstein on August 06, 2020, 07:21:14 pmAH are on order ata december 2020.H are indeed in stock, 395pcs (7-8-2020)

author: martinr33
author_rank: Frequent Contributor
timestamp: August 07, 2020, 07:16:46 pm
content: I have not used Bristol, but they look legit. Line card, photos of a facility that looks plausible. They are worth a call.When you use a Chinese supplier, there's a good chance that you will get refurbs or remarks. Marking up to the A version costs nothing more than regular, and attracts a higher price.

author: Andreas
author_rank: Super Contributor
timestamp: August 07, 2020, 08:10:30 pm
content: Hello Ian,for production I would only use parts from authorized distributors.Findchips distinguishes between authorized distributors and independent dealers/brokers.https://www.findchips.com/search/lm399when measuring over 15 to 40 deg C with a LM399 (non A) I have typically a zero T.C. or up to 2 ppm over a 25 deg C range.From 5 samples the worst case was 40uV (20uV after 2:1 divider) = 6 ppm over 25 deg C range giving less than the "typical 0.3ppm/K" from the data sheet.with best regardsAndreas

author: IanJ
author_rank: Unknown
timestamp: August 07, 2020, 09:37:45 pm
content: Thanks for all the help and suggestions folks......I am just too nervous to buy from a non authorised dealer.....who knows what I'd get if I did get anything. Yes it's for production.Also not happy at using the non-A 2ppm version, the selling point of my voltage sources is partly the stability and I advertise it with the AH version.....and it would play on my mind too much.Guess I just wait for stock.Frustrating thing is I just bought 25 from Digikey just a few weeks ago......if only I'd known.PS. I have a begging email in with Analog Devices Inc......surely they have some in a drawer somewhere.....Ian.

author: Microcheap
author_rank: Frequent Contributor
timestamp: August 08, 2020, 12:09:05 am
content: UTsource claims to have it in stock, certified and with a 90 days return and refund guarantee:https://www.utsource.net/itm/p/11732139.html

author: wraper
author_rank: Unknown
timestamp: August 08, 2020, 12:24:38 am
content: Quote from: Microcheap on August 08, 2020, 12:09:05 amUtsource is not that much better than ebay and aliexpress. Full of counterfeit shit.

author: IanJ
author_rank: Unknown
timestamp: August 08, 2020, 07:04:29 am
content: Quote from: wraper on August 07, 2020, 11:52:34 amI got a reply from Ebay seller, confirmed they were refurbished.Ian.

author: Kleinstein
author_rank: Super Contributor
timestamp: August 08, 2020, 11:09:08 am
content: The LM399A should be just a graded version of the LM399.With the 399 reference circuit changes are the TC depends more on the thermal design, than on the chip. One could do a crude binning before from the absolute voltage level. There is quite some correlation between the voltage and the TC without temperature stabilization.Depending on the circuit it is used in one may do a little more grading / testing on the ready made circuit instead of a tighter binned reference.

author: TheDefpom
author_rank: Frequent Contributor
timestamp: August 14, 2020, 02:41:26 am
content: I would also suggest Arrow, I used them once (so far) and was very happy with the service etc.Unfortunately LM399AH#PBF are not in stock right now either...https://www.arrow.com/en/products/lm399ahpbf/analog-devices

author: TheDefpom
author_rank: Frequent Contributor
timestamp: August 14, 2020, 02:46:37 am
content: In regards to UTsource, I have used them several times to get hard to find parts and never had an issue, just make sure you choose utsource certified original part as the supplier and not some 3rd party one which is also listed in the results.UTsource show this for the item you want:https://utsource.net/itm/p/11732139.htmlPersonally I would be fine buying them from utsource.

author: TheDefpom
author_rank: Frequent Contributor
timestamp: August 14, 2020, 02:58:03 am
content: And of course if you get really desperate you can get the LM399H#PBF from RS UK:https://uk.rs-online.com/web/p/voltage-references/1450736/

author: IanJ
author_rank: Unknown
timestamp: August 14, 2020, 01:44:24 pm
content: In general yes, but not LM399AH as they are too easy to fake from a LM399H or iffy units and not so easy to test properly and to categorise when it's qty=30.These are not just for me, its for production and my customers.......No worries though, my bulk purchase customer say they can wait.......all is good.My only other option would have been to redesign with the LTZ1000 but they are nearly 50quid a pop. Maybe a future idea though......Ian.

author: IanJ
author_rank: Unknown
timestamp: August 18, 2020, 06:06:31 pm
content: Update:Just got an email from Digikey.......55off LM399AH......Shipped, salesorder complete......Digikey site still shows zero stock, invoice says shipped from the Philippines.I knew there was a bunch in a drawer somewhere!Ian.

author: TheDefpom
author_rank: Frequent Contributor
timestamp: August 18, 2020, 07:58:33 pm
content: Nice

author: IanJ
author_rank: Unknown
timestamp: August 21, 2020, 11:14:49 am
content: They arrived from Digikey today.......Check the date code!

author: wraper
author_rank: Unknown
timestamp: August 21, 2020, 11:31:15 am
content: Quote from: IanJ on August 21, 2020, 11:14:49 amAnd what's surprising about it? I've received parts which were manufactured a week or two ago.

author: IanJ
author_rank: Unknown
timestamp: August 21, 2020, 11:38:42 am
content: Quote from: wraper on August 21, 2020, 11:31:15 amJust wondered why they have run out worldwide if they only made them 11th week 2020. Maybe the batches aren't that big.Ian.

author: IconicPCB
author_rank: Super Contributor
timestamp: August 22, 2020, 05:52:30 am
content: Check for moisture behind the ears

author: IanJ
author_rank: Unknown
timestamp: August 25, 2020, 09:45:00 am
content: Hi all,So for fun I ordered 1off LM399AH from Ebay (China) sold as refurbished.Some photos below, the first two photos show a genuine new LM399AH on the left for ref.

author: TheDefpom
author_rank: Frequent Contributor
timestamp: August 25, 2020, 10:25:37 am
content: Are those extensions soldered onto cut down legs or are those just covered in solder?

author: wraper
author_rank: Unknown
timestamp: August 25, 2020, 10:27:05 am
content: Quote from: TheDefpom on August 25, 2020, 10:25:37 amThey are iron legs welded on top of original kovar, not soldered.

author: IanJ
author_rank: Unknown
timestamp: August 25, 2020, 10:37:48 am
content: Well, here's another couple of close-ups.....best I can do with my phone LOL!I wicked the top most leg as far up to the body as I could. I haven't touched the other legs.

author: SilverSolder
author_rank: Super Contributor
timestamp: August 25, 2020, 04:00:50 pm
content: Does it actually work?

author: notfaded1
author_rank: Frequent Contributor
timestamp: August 25, 2020, 07:47:41 pm
content: The holes on the case don't even look right... the real part has much tighter tolerance around the leads than the "special" part.Bill

author: FriedLogic
author_rank: Regular Contributor
timestamp: August 25, 2020, 08:39:14 pm
content: Yes, the case is a big give-away with these parts. However, there are not usually photos of the bottom of the case in the listing, and the photo in the listing is often not of the part they will send anyway. To further complicate things, the case of the 'real' parts don't all look the same either.The legs on that one don't look too bad. They were so cheap that I got one or two from a few different sellers to see if any were as advertised. They appeared not to be - although the ones that I tested seemed to work reasonably.

author: SilverSolder
author_rank: Super Contributor
timestamp: August 25, 2020, 10:15:37 pm
content: Quote from: FriedLogic on August 25, 2020, 08:39:14 pmIn principle, there is no reason a salvaged component wouldn't "work"... there is rather a lot of uncertainty associated with the specification, though!

author: MadTux
author_rank: Frequent Contributor
timestamp: August 25, 2020, 10:22:33 pm
content: Usual ebay-china garbage. The worst thing is that their "refurbishment" ruins components that otherwise might have been usable. But with legs cut and welded and with original part number errased, it's nothing but trash. Welded legs introduce thermal voltages in this instance and erased part numbers makes it impossible to tell, what the stuff really is. Like getting a transistor with lower voltage rating that does even more damage to a repair project.BTW, I wonder what nice things were destroyed to get those LM399s?

author: SilverSolder
author_rank: Super Contributor
timestamp: August 25, 2020, 11:40:12 pm
content: Quote from: MadTux on August 25, 2020, 10:22:33 pmSome things, we are better off not knowing!

author: guenthert
author_rank: Frequent Contributor
timestamp: August 25, 2020, 11:45:16 pm
content: Quote from: MadTux on August 25, 2020, 10:22:33 pmThe legs are the same length and look to be the same material, thermal EMF shouldn't be a problem here. It shouldn't be too difficult to verify that it is indeed a LM399.Quote from: MadTux on August 25, 2020, 10:22:33 pme-waste from around the world, 'cause others couldn't be bothered to repair those "nice things".

author: wraper
author_rank: Unknown
timestamp: August 26, 2020, 12:04:47 am
content: Quote from: guenthert on August 25, 2020, 11:45:16 pmLegs are not from the same material. It's crappy iron instead of kovar unless you are extremely lucky. And I doubt they would go for extra length considering crappy thermal shield which yells fake. You can look at some examples at pages 59-63.https://www.cti-us.com/pdf/CCAP-101InspectExamplesA6.pdf

author: KK6IL
author_rank: Regular Contributor
timestamp: August 26, 2020, 04:16:20 am
content: The 4 pieces I bought on Ebay, recycled from China, from<https://www.ebay.com/itm/1x-LM399H-Precision-Reference-LM399/121069770252?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649>were as pictured in his ad with short leads. 3 look good during burnin, the 4th is untested as the leads were too short for the breadboard. Photo of test fixture and HP3456 in ad implies parts are tested. He has lots of other references offered.<https://www.ebay.com/str/HIFI-AUDIO-IC/Voltage-Reference/_i.html?_storecat=2603363012>

author: guenthert
author_rank: Frequent Contributor
timestamp: August 26, 2020, 04:58:30 pm
content: Quote from: wraper on August 26, 2020, 12:04:47 amThe legs are each the same combination of materials, which is what matters.I'm not sure what you mean by 'fake'? The product was announced as refurbished, which it appears to be. I don't see any indication of a counterfeit product or misleading advertisement.

author: wraper
author_rank: Unknown
timestamp: August 26, 2020, 05:24:51 pm
content: Quote from: guenthert on August 26, 2020, 04:58:30 pmPrinting LT logo and fake date code over a non original enclosure is an act of counterfeiting. Not to say AH suffix most likely is not what an original part had. Tampering with thermal shield and terminals is damaging to component performance and leg reliability against breaking.QuoteNope, for it to not matter, thermal gradient over such material junctions must be equal across the legs for thermal EMF to cancel out. And good luck with achieving that perfectly, especially considering that these welded junctions are very close to the heated package.

author: Kleinstein
author_rank: Super Contributor
timestamp: August 26, 2020, 05:33:23 pm
content: The replaces leads can cause extra thermal EMF.One the good side, a reclaimed part is likely already burned in for some time. So the drift could be lower - though not for sure.

author: wraper
author_rank: Unknown
timestamp: August 26, 2020, 05:38:25 pm
content: Quote from: Kleinstein on August 26, 2020, 05:33:23 pmYou can simply buy used as already suggested without any of this BS. Also terminal welding and leg tinning very close to the package can cancel out all of the burn in parameter stabilization and part may need a new burn in to stabilize again.

author: guenthert
author_rank: Frequent Contributor
timestamp: August 27, 2020, 09:11:23 pm
content: Quote from: wraper on August 26, 2020, 05:24:51 pmI'd say it can be argued and I'd guess the seller would, that this is an act of refurbishing. In fact, the buyer would want to know who originally made the product (and the LT logo indicates that -- it is an LT product after all). And we don't know that the date code is fake. It might very well be the date of the original, albeit I concede, I would be surprised if the seller would put that much effort into the refurbishing process.Quote from: wraper on August 26, 2020, 05:24:51 pmWhat makes you think that? Just a few comments above you can see a photo of a new, genuine part which has that very same suffix.Quote from: wraper on August 26, 2020, 05:24:51 pmIt is refurbished. No-one guarantees and no one expects that it performs as well as a new product.Quote from: wraper on August 26, 2020, 05:24:51 pmSame combination of materials and same length of legs (as I already wrote),willensure that the EMF cancel.Quote from: wraper on August 26, 2020, 05:24:51 pmPerfection is for the gods. We're talking about LM399, not Josephson junctions here.

author: wraper
author_rank: Unknown
timestamp: August 27, 2020, 09:43:03 pm
content: Quote from: guenthert on August 27, 2020, 09:11:23 pmBullshit. There is like 60oC to drop over the legs (at room ambient temperature). Either you did not read what I wrote or refuse to switch your brain on. You have thermocouple junctions in middle of the legs and each junction is at somewhat different temperature. There is no perfect matching of this welding bullshit.QuoteH is prevalent and AH is more expensive.QuoteReally? If I buy LM399AH, I expect it to perform according to LM399AH specs. It may be not perfect visually but actual operation must be up to spec.

author: IconicPCB
author_rank: Super Contributor
timestamp: August 27, 2020, 10:35:12 pm
content: Another well socialised response.

author: MadTux
author_rank: Frequent Contributor
timestamp: August 27, 2020, 10:42:46 pm
content: That's just the truth about the garbage that comes from china.That guy seems the rare exception, since I think he honestly cares about what he sells:https://www.ebay.com/itm/1x-LM399H-Precision-Reference-LM399/121069770252?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l264960°C at that welded junction can easily make a few mV, a mV on a 7V device is about 150ppm. And since LM399s are frequently used on instruments accurate to about 30-10ppm, it matters, I think.N-type thermocouple has 1.6mV at 60°C and it uses quite similar metals, NiCrSi-NiSiOne leg soldered to large pad that acts as heat sink might be enough to unbalance the thermocouple pair on both legs to get significant instability.

author: FriedLogic
author_rank: Regular Contributor
timestamp: August 27, 2020, 11:45:07 pm
content: It's a bit pointless arguing about the TC and thermocouple effects on the performance without knowing the material used in them or the way that it's finally mounted on the PCB. I tried one for some weeks along with a new LT LM399AH and although the TC for around 25-50°C was a little worse it did not have the popcorn noise that the new one had.I cut one open and it was marked LT on the die, but the fake case was marked NS.2015 NS parts are amusingReclaimed parts may have suffered a lot, and the 'refurbishment' only adds more. I noticed that someone doing high temperature tests on them got a lot of furry corrosion on the leads too. Others mentioned that the legs came off on some, so long term stability could be another problem.Overall, I would much prefer just plain used parts to refurbished ones, but they are usually way too close to the price for new ones. Refurbished ones are a curiosity, but add too much uncertainty for my liking.

author: Kleinstein
author_rank: Super Contributor
timestamp: August 28, 2020, 07:01:09 am
content: Chances are the reclaimed parts are a random mix of 399AH and 399H from different ages with both LT and NS parts. The honest way would be to mark them as something like LM399R or something similar without man manufacturer logo. This could avoid legal problems.Anyway for a demanding use one would get the parts from a reliable source or at least do testing one all parts. Even the original ones can show higher drift or excessive popcorn noise.Welding the new leads could be quite some stress too. If the wires are iron and not Kovar like the original there will be some additional thermal EMF. However like with the original, the thermal EMF will cancel out to a large part with a symmetric setup. Iron / steel is usually in between Kovar and copper for the thermal EMF. So the difference is not that large.For most purpose I would consider the reclaimed parts lower grade than the non A. Even if they were original AH parts, that small difference is probably lost.

author: Andreas
author_rank: Super Contributor
timestamp: August 28, 2020, 07:32:36 am
content: Quote from: Kleinstein on August 28, 2020, 07:01:09 amHow do you guaranty a symmetric setup when one pin is directly connected to the case bottom of the LM399?And the others have probably different lengths from the bottom to the welding point.with best regardsAndreas

author: IanJ
author_rank: Unknown
timestamp: August 28, 2020, 09:41:47 pm
content: I am not so much interested in how it performs, but rather what did I actually get? Is there an easy way to see diff between AH and non AH if I take the top off the can?Ian.

author: wraper
author_rank: Unknown
timestamp: August 28, 2020, 09:52:35 pm
content: Quote from: IanJ on August 28, 2020, 09:41:47 pmNo, it's exactly the same IC with the same die in the same package. AH is simply tested/binned to tighter spec. But it does not mean that H cannot outperform AH, it's simply thatguaranteedspecs are tighter.