LM2594 - what the hell is wrong with the device? Fake? Devil's custom pinout? - Page 1
Forum section: electronics / projects

author: Yansi
author_rank: Super Contributor
timestamp: November 29, 2015, 12:03:14 am
content: Hello!I have just finished soldering one of my relaxation projects, and proceeded to put some volts into it. But whatta?! Dead short in between GND and the circuits V+ supply line. After a small investigation composing of desoldering and resoldering various components, I have found the root cause: The devil's LM2594M-5.0.The little bastard has dead shorted pin 5, 6, 7 and 8. After I cracked the chip open, the reason for the short is obvious. Pins 5 to 8 are connected to the substrate sheet metal. At first, I thought well, a chinese piece of crap without a silicon (we already knowthe famous atmega328p slug with a lump of copper instead of a silicon chip) but it seems there really is some sort of chip.After some more measurements, it turnes out that pin 3 against the substrate pins (5 tomeasures suprisingly close to 10k ohms. That got me suspicious again: What is the feedback resistor divider in the original part? The datasheet says 7.6k and 2.5k. Thats a close shot! Other pins against the substrate mease some tens of Mohm. There must be something inside. Maybe a LM2594 with custom pinout?Have you ever seen something like this? What the hell is going on? I tried to look up some different vendor datasheets, but all of them share the same standard pinout. Not this devil's one.Anyone interested would like to decap the bastard and put it into a microscope to identify it? I still have 9 pieces of this devil's chip. I may send you some for investigation. Unfortunately I have no such equipment nor the highly corrosive chemicals to decompose the package.Here's the cracked puppy!

author: xZero
author_rank: Contributor
timestamp: November 29, 2015, 12:06:24 am
content: Have you got it from Aliexpress, Ebay or any other Chinese site?

author: Yansi
author_rank: Super Contributor
timestamp: November 29, 2015, 12:18:56 am
content: I don't know exactly where they are from, but it's quite possible they are direct sourced from china through ebay or so. They have been laying in my drawer quite some time. I have sourced many of these LM25xx regulators from china for hobby projects, never was a problem. Until now.(Note: I have also spotted a HV version of LM2596 regulator, that is clearly not officially listed at the original manufacturers product pages from TI, NSC nor ONS)I have also tried to search for any signs of a chinese "co-production" of these but no luck finding anything about them.I know china produces huge amounts of these small switchers, for example the XLSEMI company is quite known... But their devices are clearly not intended to be a cheap fakes, they have their own series of quite respectable products...

author: sleemanj
author_rank: Super Contributor
timestamp: November 29, 2015, 12:24:10 am
content: Die and carrier rotated 180' in the package maybe (manufacturing or re-marking error)?

author: wraper
author_rank: Unknown
timestamp: November 29, 2015, 12:53:59 am
content: Just some other IC with marking replaced by counterfeiters. Image is not too clear but the top of the IC looks sanded. They either sand off the top or wash the old marking with solvents if possible.

author: xZero
author_rank: Contributor
timestamp: November 29, 2015, 01:06:15 am
content: I have recently got 10x LM338T for cheap as 4USD (eBay, 90k seller). However those seems to be either fake or damn low quality, since those suffers to output even low current as 1.5A... Two in parallel delivers 3A at max, while just one genuine TI LM338T delivers 5A (7A peak). Seems like LM317 labeled as LM338T.Your case seems to be pure scam, I got at least barely working parts. Parts you got are horrible. Too bad you cannot discover where you got them from... Pins attached to metal sheet? God, that's........ I have no words to describe..

author: SharpEars
author_rank: Unknown
timestamp: November 29, 2015, 02:08:25 am
content: If it's an IC or other active semiconductor and it's from China (or any other asian country), it's 100% guaranteed fake with zero exceptions. If it's from the US and is being sold on eBay, it's 95% guaranteed fake (if you know how to spot a fake and the seller takes pictures of the actual parts, you can filter for the 5% that are genuine based on the images - it is possible, but assumes you have access to 100% genuine parts and know exactly how all fonts, pins and even the color, alignment and positioning of the text and logo on the part should look).If you want a high likelihood of genuine parts, buy them from a genuine distributor (at least 5-10% guaranteed fake). There is no sure thing other than sourcing from the manufacturer (0.1% guaranteed fake, due to them being manufactured in China) or no more than one hop from the manufacturer (i.e., direct distributor that sources from the manufacturer) (1-2% guaranteed fake).You can fight these deceptive practices by buying asian parts on eBay and getting a 100% full refund after the parts arrive due to them being fake, but keeping the parts due to the draconian eBay buyer protection measures. In fact, I completely condone this practice to put the scammers out of business.Counterfeit electronics should be made illegal!

author: georges80
author_rank: Frequent Contributor
timestamp: November 29, 2015, 03:14:46 am
content: Quote from: SharpEars on November 29, 2015, 02:08:25 am5-10% fake from a distributor (e.g. Digikey/Future/Mouser/Allied/Avnet etc) - no idea where you are getting those statistics.I've been using distributors for decades and have never received a part from them that didn't meet spec or work to spec. Occasionally a distributor may pull the incorrect part - which is generally dealt with expediently, but that is of course not counterfeit issue. A genuine distributor can track the part back to the manufacturer with lot codes, date codes etc. Parts are also stored/shipped appropriately (ESD/humidity etc etc).It's the grey market that you are open to problems since many/most parts are bought as excess inventory or from more dubious sources. Buying components on ebay and various asian websites, well, I can understand folk trying to save a buck or don't have access to distributors locally, but in that case you need to assume the parts you are getting could be total garbage, 2nds etc. No point complaining or acting surprised. Don't want to order/wait weeks/build project and then find nothing works or works poorly then buy from a reputable distributor.cheers,george.

author: amyk
author_rank: Super Contributor
timestamp: November 29, 2015, 05:09:19 am
content: That looks like a standard SOIC-8 MOSFET. Are pins 1-3 also connected together, and pin 4 has (if the gate oxide is still intact) no continuity with the others?

author: wraper
author_rank: Unknown
timestamp: November 29, 2015, 09:35:48 am
content: Quote from: SharpEars on November 29, 2015, 02:08:25 amWhat a BS

author: Ian.M
author_rank: Super Contributor
timestamp: November 29, 2015, 09:44:08 am
content: You can decap chips without strong acids or other highly toxic chemicals.See:https://ms3c.wordpress.com/2010/07/15/boiling-chips-in-tree-sap/

author: Yansi
author_rank: Super Contributor
timestamp: November 30, 2015, 12:51:47 pm
content: Okay I've finally tracked down where these are from: Aliexpress. The good thing is I already received a refund, due to extreme long delivery time. (Parts arrived after the refund).Also it seems it's not a mosfet, as there are no three shorted pins for the source and the pin 3 measures 9,98kohm to ground (which is surprisingly close to what the voltage divider should measure in a genuine LM2594M-5.0 device). The rest three pins measures some megaohm-ish values.Maybe I will play with them a little: Let's suppose they are a custom pinout of a genuine LM2594. So I'll try to find what the pinout is. Shouldn't be that hard, only 5 pins and not so much combinations.I have also looked at these under my shitty microscope. The package seems not to be sanded down and the laserprint is pretty uniform over all of the devices.The only problem pissing me of now is that I have to buy this convertor from some more reliable distributor. These old rusty switchers cost a fuckton of money. ($4+ each). That is not fucking acceptable, never going to use these in any of my designs.//EDIT: Look what we have on Aliexpress: They all look the same.http://www.aliexpress.com/wholesale?catId=0&initiative_id=SB_20151130045430&SearchText=lm2594m-5.0With only one noticable difference: The pin 1 dent differs in size. Some products has small dent (like those I have), some has a big dent. All of them are the same marking, only different date/lot code (four top characters).

author: Fungus
author_rank: Super Contributor
timestamp: November 30, 2015, 03:57:47 pm
content: Quote from: SharpEars on November 29, 2015, 02:08:25 amComplete rubbish. I've bought loads of chips/MOSFETs/etc. on eBay. So long as you avoid the people who sell big expensive parts for $1 each then you'll be OK.I've only had a couple of bad lots out of hundreds of purchaes... and some lots were obviously second hand. They're the minority though, and they're half DigiKey price so I'm not complaining (you can get refunds anyway).If you're manufacturing large batches of PCB then it's probably not a good thing to source parts on eBay. For a hobbyist it's not really a problem, andnowhere near100%.

author: Yansi
author_rank: Super Contributor
timestamp: November 30, 2015, 11:03:22 pm
content: So I went to a local electronics store (our local "Jaycar" equivalent) and bought two f...g pricey LM2594M-5.0. I can tell you, they look exactly the same as those from AliXpress. Stay tuned, I'll make some closeup photos to compare the prints and also will measure and test them.Yan

author: georges80
author_rank: Frequent Contributor
timestamp: November 30, 2015, 11:23:42 pm
content: Looks means nothing... I had a run of 250 boards assembled in China before I requested all parts to be purchased in the US from Digikey/Mouser/etc and shipped to China. That run of boards, all did not function. There was an NS switcher IC on it that wasn't working unless I floated a couple of NC pins - never had to do that on previous use of that chip/design.I live near NS (or where NS was before it was absorbed by TI). I contacted their failure analysis lab and sent it some bad parts and some 'authentic' parts. They x-rayed the parts and confirmed that the bad parts did NOT contain actual NS dies, even though the external markings all looked authentic. The assy house confirmed the bad parts had been sourced on the grey market in China...The assy house reworked all the boards and used authentic parts, all boards then worked correctly.So, no idea what was in the fake parts, it was something 'close' to what was meant to be in there - but not the real thing.Live and learn. The counterfeit semiconductor market is real.cheers,george.

author: amyk
author_rank: Super Contributor
timestamp: December 01, 2015, 08:35:01 am
content: NC really means "do NOT connect", you could've just as well received the message "these are real parts, we changed the silicon slightly but you're using them wrong"

author: Monkeh
author_rank: Super Contributor
timestamp: December 01, 2015, 08:51:44 am
content: A lot of datasheets specify NC as no connect or ground.

author: bktemp
author_rank: Super Contributor
timestamp: December 01, 2015, 09:36:23 am
content: Quote from: Monkeh on December 01, 2015, 08:51:44 amI have seen datasheets specifying NC as do not connect or as not connected or even as connect to GND. It depends on the manufacturer and the specific part.Many power ICs use the GND pins as heat sinks, therefore suggesting to connect them to the GND plane. Precise analogue ICs use NC pins for post package trimming (many voltage reference ICs do this), those pins must not be connected. Even small leakage currents into those pins make the output voltage drift out of specs. I have also seen datasheets recommending NC pins for signal routing to simplify the single layer layout.There are often improved versions of ICs with additional features connected to the NC pins from different manufacturers. They often are compatible as long as the NC pin is floating.If the datasheet does not tell you exactly what is connected to NC pins, do not connect them.

author: Fungus
author_rank: Super Contributor
timestamp: December 01, 2015, 09:45:08 am
content: Quote from: georges80 on November 30, 2015, 11:23:42 pmNC means "No Connect" - they're supposed to float. Connecting them to GND is wrong (and so is tying them to Vcc!)

author: Yansi
author_rank: Super Contributor
timestamp: December 01, 2015, 10:28:36 am
content: Based on what?Look in the LM2594 datasheet. See the pins 1 to 3? They are all NC. They are suggested to be soldered to board. Guess where they are connected on the reference PCB design: Ground!Y.

author: Fungus
author_rank: Super Contributor
timestamp: December 01, 2015, 10:52:35 am
content: Quote from: Yansi on December 01, 2015, 10:28:36 amWhich manufacturer? The reference circuits of TI and ONSemi don't have them connected to anything.http://www.ti.com/lit/ds/symlink/lm2594.pdfhttp://www.onsemi.com/pub_link/Collateral/LM2594-D.PDFTI says "No internal connection, but should be soldered to pc board for best heat transfer" but not GND.The people who made your "fake" part obviously didn't see your "reference PCB design". They only read the datasheets.

author: Yansi
author_rank: Super Contributor
timestamp: December 01, 2015, 12:33:40 pm
content: Page 30, look, carefuly.QuoteI don't get the context of that... There's nothing wrong with grounding or whatevering pins 1-3. Genuine part will work. The chinese crap has shorted pins 5 to 8 and seems to use pins 1 to 4 instead. Jeeeez, I already explained.

author: georges80
author_rank: Frequent Contributor
timestamp: December 01, 2015, 04:33:31 pm
content: Quote from: Fungus on December 01, 2015, 09:45:08 amIf you don't know, don't write... Mine was an example of a NS part, the LM2674/75 to be specific.The pins are marked NC which means 'not connected', and NS TELLS YOU TO GROUND THEM FOR BETTER THERMAL PERFORMANCE.DNC means 'do not connect'.cheers,george.

author: bktemp
author_rank: Super Contributor
timestamp: December 01, 2015, 05:41:32 pm
content: Quote from: georges80 on December 01, 2015, 04:33:31 pmIn this case yes. But NC can also mean do not connect. The datasheet for the classic REF02 voltage reference says:QuoteIf the datasheet explicitly says NC pins are not connected then you can connect them to GND or use them for signal routing, but without any further information NC pins should always be treated as do not connect.

author: georges80
author_rank: Frequent Contributor
timestamp: December 01, 2015, 06:49:29 pm
content: Yes, though I presume that most folk can read the datasheet to determine what to do if anything with NC/DNC pins, I can at least manage that minor skillcheers,george.

author: Siwastaja
author_rank: Super Contributor
timestamp: December 04, 2015, 03:52:23 pm
content: Quote from: Fungus on November 30, 2015, 03:57:47 pmYes, it's rubbish, but...QuoteThis is complete rubbish, too.The chances of getting a genuine MOSFET or simple IC (voltage regulator, etc.) on eBay is rather poor. "100% guaranteed fake" is rubbish, but I've found that the percentage is somewhere about 50% fake. Your mileage may vary, but as you can read from countless testimonies, it's damn stupid to buy simple chips or transistors from Chinese Ebay sellers, because the risk is just huge. So no, you won't "be OK". Even if the fake percentage is only 10%, it's an utter catastrophe, as you need many components in most designs and the odds add up.Have you actuallyusedthose components you have bought? Are you sure they are not fakes? Sometimes fakes are not completely broken. I have got a voltage regulator marked as 3V3 regulator, but it was a just a different voltage, but otherwise performed basically OK. I have got TO220 MOSFETs (IRFZ44 or such) which just simply had 3-4 times the specified Rds(on), so a different, kinda-like mosfet with lower specs with fake markings. In my application, they worked but I had to add extra heatsinks. Stuff like this. Sometimes a voltage regulator which may be "good enough"; only oscillates a little bit, maybe the voltage is off the specs, but not too much, etc...Then there are chips that don't work at all. These get most of the attention on the forums.The prices are relatively close to the Digikey/Farnell/Element14 prices, but for smaller batch size, and no postage fee hell. That's why it's tempting to buy those parts, but I stopped doing that since the risk is simply too big. Don't get me wrong, there are many things I buy from Chinese eBay sellers, such as many types of connectors (usually usable quality for 90% lower price!!), LEDs (taking a well-known risk that they are from the reject bin; I have about 5-10% failure rate on eBay LEDs). But discrete semiconductors? Never again!You can get refunds, but only during limited time. You need to come up with a test bench capable of actually measuring the parameters that are important to you, and test the components as quickly as possible. This is a huge waste of time. I have planned doing it so many times, and in the end, never did it.QuoteFor me, as a hobbyist, it was a huge problem. As a hobbyist, I want components that perform at least relatively close to the spec. I don't want to spend my precious free time fighting with broken products, when no one pays me for it. But maybe for some the hobby is only building the nice-looking 3D mockup, in which case the eBay components work just fine, as they don't need to, well, work at all.

author: Ian.M
author_rank: Super Contributor
timestamp: December 04, 2015, 03:59:38 pm
content: Hobbyists have a long history of buying factory floor sweeping or worse. e.g. just about any Radio Shack/Tandy branded IC or transistor, or what about 'lucky' bags - you are lucky if you can find data on half the contents and maybe half of that half will actually work and meet specs.

author: SeanB
author_rank: Super Contributor
timestamp: December 04, 2015, 05:48:23 pm
content: Sinclair started out doing the same, buying job lots of failed transistors ( which is why all of his early radios and such have unmarked semiconductors in them) then retesting then to get those that were not quite dead short or open, and which had a little gain and not too much leakage. Carried this on with all the stuff he made, using parts at the limits of the rating envelope, or even beyond it.

author: mikerj
author_rank: Super Contributor
timestamp: December 04, 2015, 06:20:24 pm
content: Quote from: SeanB on December 04, 2015, 05:48:23 pmDefinately. Sinclairs X10 Class D power amp would inevitably blow up if you tried to extract the rated 10 watts from it. No RF filtering either. That said the guy was a visionary; the X10 came out in the late 60's IIRC, and it's only in the last 10-15 years or so that class D audio amps have become really widespread.

author: AlxDroidDev
author_rank: Frequent Contributor
timestamp: December 04, 2015, 06:54:17 pm
content: Most (if not all) Arduino/Raspberry Pi shields bought from Aliexpress, DX, ebay, etc, that have an IC on it, use fake ICs. I have a couple fake MAX7219 and UN2003. The MAX7219, specially, looks different from the original, works almost the same, but fails after a few weeks. The more common a component is, the higher the chances of it being a fake.

author: Ian.M
author_rank: Super Contributor
timestamp: December 04, 2015, 07:06:13 pm
content: Quote from: AlxDroidDev on December 04, 2015, 06:54:17 pmAlmost certainly not true. I strongly suspect that it resembles a bathtub curve only with a steep cutoff before the peak at the most popular end. If a high demand jellybean part is cheap enough, it wont attract fakers because they can make more faking parts with somewhat lower demand but a higher margin.At the other end, there are the more valuable rare discontinued 'NOS' fakes, that are profitable even for small 'kitchen table' operators.

author: wraper
author_rank: Unknown
timestamp: December 04, 2015, 07:25:05 pm
content: Quote from: Ian.M on December 04, 2015, 07:06:13 pmConsidering they sell even used SMD capacitorshttp://rube.asq.org/asd/2009/03/compliance/counterfeit-parts.pdfthey do counterfeit everything. I consider relatively safe only the parts which are hard to counterfeit, like MCUs, stepper motor drivers (need to at least manufacture a compatible clone). Though they manage to counterfeit even very specialized parts, like this one:http://zeptobars.ru/en/read/Nordic-NRF24L01P-SI24R1-real-fake-copyEverything what can be replaced with some inferior part and will seem to work is no way to buy: opamps (except very special cases), voltage regulators, transistors, voltage references.