[solved!] MAX134CMH Pinout (QFP44) - nowhere to be found? - Page 1
Forum section: electronics / projects

author: Yansi
author_rank: Super Contributor
timestamp: December 25, 2016, 02:22:19 pm
content: HelloI have recently helped a colleague to diagnose a damaged multimeter. We have found MAX134 chipset inside. We have looked for the datasheet and sure, found it here:https://datasheets.maximintegrated.com/en/ds/MAX133-MAX134.pdfBut wait, where's the QFP package pinout?The chip inside the multimeter was a MAX134CMH, a QFP44 package. But that is not listed in the datasheet. We have tried to figure out if the pinout was the same as on the PLCC44 chip, but it seems that nope.Also the PLCC has the pin 1 in the middle of one side, whereas the QFP in one of the corners. Even if we assumed the pin numbering is just shifted half side compared to the PLCC, nope, it didn't fit. Some unused pins where elsewhere than on the PLCC, etc..Why the datasheet does not list the CMH suffixed chip? It seems impossible to find the pinout. Though the chips are still available from china suppliers and some distributors like Mouser in small quantities (leftover stock). Do you have any idea, why is the pinout of the QFP44 variant missing completely? //EDIT: The QFP44 version of the chip is still in production, according to MAXim IC website//Bottomline: I do not really need to find the pinout, just out of pure curiosity, if someone knows, whats up with it. The multimeter was already tossed in a scrap bin. (the chip itself is most probably faulty - as no obviously faulty components were found around it, except a blown fuse on the smaller current range)Just out of my another curiosity, as the MAX134 seems to be quite outdated and old,no longer madeit is actualy in production still, what is the most common multimeter chipset used today in similar lowend multimeters?Thank youYansi

author: Yansi
author_rank: Super Contributor
timestamp: December 25, 2016, 03:35:36 pm
content: After some hours of digging through the web, I have finally and quite accidentally found the pinout of the QFP44 (CMH suffix). It seems to match what was in the multimeter.page 19 here:http://www.produktinfo.conrad.com/datenblaetter/125000-149999/126560-sp-01-en-DG_SCOPE_20MHZ.pdfor the screenshot from it, if the link goes dead:

author: KhronX
author_rank: Frequent Contributor
timestamp: December 25, 2016, 04:16:47 pm
content: One possibility might be the old ICL7106 / ICL7107 (or rebrands of them).http://www.intersil.com/content/dam/Intersil/documents/icl7/icl7106-07-07s.pdfQuote from: Yansi on December 25, 2016, 02:22:19 pm

author: Yansi
author_rank: Super Contributor
timestamp: December 25, 2016, 04:34:53 pm
content: That is just a standalone voltmeter. Sure, this one gets the most use in the cheap'o'meters. I meant more like those "analog frontend only" chips, without LCD/LED driving capabilities. Like the MAX134, that comprises of an integrating AD converter, range switches, filters.. and other analog for measuring ohms or so + a way to interfacing it to a host MCU, that des the LCD driving business etc.

author: KhronX
author_rank: Frequent Contributor
timestamp: December 25, 2016, 04:37:28 pm
content: Ah, right, that's a bit different then"Multimeter chipset" sounded to me like an all-in-one solution - which is exactly what gets used in low-end metersWell, those and/or anonymous chip-on-board dies...Separate front-end chips are, i believe, rarely found in low-end meters. TWO chips are more expensive than one

author: JoeN
author_rank: Frequent Contributor
timestamp: December 26, 2016, 06:53:43 am
content: That is really odd. The QFP is listed in stock and for sale both on Maxim's site and also at Digikey. The datasheet linked from both sites is that old one you linked earlier that has no mention of the QFP part, much less the pinout.http://www.digikey.com/product-detail/en/maxim-integrated/MAX134CMH-D/MAX134CMH-D-ND/1701926I can only infer that it hasn't been updated because nobody has complained because nobody has bought that part in a decade. Why would you?

author: Yansi
author_rank: Super Contributor
timestamp: December 26, 2016, 12:53:51 pm
content: Why would I? I don't know... maybe I could try to build myself a multimeter.Never built one (but I tried integrating voltmeter once!) and the MAX134 seems quite friendly for such task. Or are there any more modern alternatives to this one? (That was why I have asked about the common used multimeter chipsets - cause I could find almost none, except some crazy chinese chips like from Cyrustek)That also reminds me of something! But will create separate thread for it.//EDIT:https://www.eevblog.com/forum/projects/voltmeter-input-resistors-and-strange-color-bands/

author: JoeN
author_rank: Frequent Contributor
timestamp: December 27, 2016, 06:33:25 am
content: Quote from: Yansi on December 26, 2016, 12:53:51 pmIt seems to me, the best way to build a multimeter these days is a good quality 18 to 24-bit ADC and a fairly inexpensive microcontroller. Together, they are going to give you a lot more accuracy than a MAX134 and even cost less, though you are buying yourself a programming job, though probably not a very complex one. The upside is you can add any and every feature you ever want into your multimeter, and keep adding features going forward, all in software.

author: Yansi
author_rank: Super Contributor
timestamp: December 27, 2016, 11:15:30 am
content: Quality ADC you say? And what about the frontend? I think the ADC is the least (but not last) problem in such design. Of course, one can make the frontend from "almost discretes" and use a fuckton of MUXes etc. But still any more integrated solution for the complex signal and range switching would help much?

author: KhronX
author_rank: Frequent Contributor
timestamp: December 27, 2016, 11:23:52 am
content: What you have to keep in mind is that "bespoke" front-end devices, in addition to being few and far between, don't have much of a market at the retail end of thingsThat, and the manufacturers who actually need it, either get said front-end chips OEM'd / custom-designed and made for them, or they just spin the silicon themselves (whichever the case may be).I hate to be raining on your parade, but that's just the reality of it

author: Yansi
author_rank: Super Contributor
timestamp: December 27, 2016, 05:36:18 pm
content: I am not against building frontends from discretes or jellybean ICs. But this time... no. Maybe some time in the futureYansi

author: shakalnokturn
author_rank: Super Contributor
timestamp: July 21, 2023, 12:18:20 am
content: I realise this is slightly outdated.Just ran into the same IC in a Finest 135 clamp meter, found a Russian forum where someone got in touch with Maxim about the QFP44 package.Here's a copy of the reply and document he received (I just love it!):"Hello Alexey,Thank you for taking the time to contact us. Maxim added this part after the datasheet was published and has not updated the datasheet yet. They did supply the attached pinout for your review.If you have any other questions or comments, please don't hesitate to contact us.Best Regards”They still haven't updated the datasheet since... No rush, procrastinate until the part is long obsolete

author: Yansi
author_rank: Super Contributor
timestamp: August 11, 2023, 06:37:27 pm
content: Awesome! Thank you for providing that. Maybe some time in the future i will get back to the project of fighting with the MAX134 chip.(Also funny how somebody wanted to hide some info in the scanned document, yet you can still easily read the text hidden behind the sticky note papers.)