Is a revision A of Silicon reliable, if there is a B? - Page 1
Forum section: electronics / general

author: luiHS
author_rank: Frequent Contributor
timestamp: June 11, 2021, 09:00:55 pm
content: Hi.As most of us know, the global shortage of electronic components is already chaotic. I am doing what I can, to redesign my circuits with the 32-bit microcontrollers that I find, very few or none at all. Everything that is BGA 0.8mm pitch is out of stock, I had to settle for buying a remainder of stock in LQFP, and what is left and nobody wants is BGA 0.65mm pitch.The fact is that there is a microcontroller reference with revision A of Silicon, of which there is a large quantity in stock. The strange thing is that they appear with the status "Discontinued", when it is a very recent microcontroller. Silicon revision B exists but sold out until the end of the year.Is it reliable to buy a revision A of Silicon, when a revision B already exists, or could it have many errors and not be useful?.It is suspicious that they have so much stock and the status is Discontinued. I have asked the supplier, but he has not answered me yet.

author: ataradov
author_rank: Super Contributor
timestamp: June 11, 2021, 09:31:18 pm
content: Why not look at the errata documents? The differences are usually clearly documented.There is no particular reason to have two revisions on the market, so older revisions are marked as discontinued, although they will be produced for years to come, since many customers would have designed them in. And especially if there are significant enough differences to cause firmware incompatibility.

author: woofy
author_rank: Frequent Contributor
timestamp: June 11, 2021, 09:33:01 pm
content: It may be just a die shrink, but it's most likely bug fixes.The only way to know for sure is to get the errata sheets for the A and B revisions and compare them.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: June 12, 2021, 12:00:41 am
content: Quote from: luiHS on June 11, 2021, 09:00:55 pmAs above, professional vendors have errata sheets, which list the changes.In most cases they are minor, and affect one peripheral, and many errata have SW workarounds.Ideally, you code your SW so it can manage with either variant.So, you need to find the errata docs and study what effect they may have.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: June 12, 2021, 04:55:22 pm
content: Die shrinks can also lead to greater susceptibility to ESD and smaller tolerances for other kind of abuse.

author: mac.6
author_rank: Regular Contributor
timestamp: June 13, 2021, 12:28:18 pm
content: The biggest issue when using Ax when there is a Bx revision is the software support.A lot of time Ax is dropped as soon as there is a B0 that fix critical bugs.

author: TomS_
author_rank: Frequent Contributor
timestamp: June 14, 2021, 06:21:23 am
content: Don't forget that later revisions can also introduce bugs, or maybe even reintroduce a bug that was fixed in an earlier revision.The latest revision is not always a silver bullet.Check errata documents to see if there is anything that will cause concern for your application. You may find that you need to accommodate some odd or changed behaviour in software between revisions.

author: Benta
author_rank: Super Contributor
timestamp: June 17, 2021, 09:19:10 pm
content: The best way to go about this is to request the PCN (Product Change Notification) from an authorized distributor (forget Alibaba et al).This document is always issued by a manufacturer when a change to part occurs. Franchised distributors (again not Alibaba et al) are obliged to check their records and send PCN copies to customers that bought the part in the past.

author: ataradov
author_rank: Super Contributor
timestamp: June 18, 2021, 12:10:25 am
content: Different revisions will not have PCNs. PCNs are issued only when something is changed about the same part number (marking, packaging).

author: westfw
author_rank: Super Contributor
timestamp: June 18, 2021, 01:31:47 am
content: Note that SOME VENDORS (cough Atmel) have been tacking on "B" suffixes where there used to be an "A", for essentially new parts with dramatically different functionality. :-((ATmega88 - ok. ATmega88P: improved low power features (supposedly) ATmega88A, ATmega88PA: die shrink/revision?, ATmega88PB: oh, we changed some of the power pins to IO pins, added some features to the UART, connected some former ADC-only pins to digital GPIO... And the 328PB - that gets additional UART, SPI, and I2C ports, two more timers, and a touch controller. Grr.)

author: Siwastaja
author_rank: Super Contributor
timestamp: June 19, 2021, 02:19:58 pm
content: Quote from: westfw on June 18, 2021, 01:31:47 amI think you are mixing up part number suffixes and silicon revision codes.ATMega328PB is a different part with a different part number than ATMega328P or ATMega328. Even in ideal world, they are not supposed to be compatible! Normal level of carefulness is enough when ordering. Every letter, number and symbol in part number matters. Always. Copy-paste the full part number. Do not assume anything else. Easy enough!This thread discusses revision codes whichare not visible in the part numberand usually are not something you can order at least through normal distributors like Digikey. Here non-compatibility is a huge issue, and some manufacturers play dirtier tricks than others. In ideal world, the parts should be 100% compatible (or the manufacturer should change the part number instead, like ATMega328P->ATMega328PB) but in reality you need to be careful, for example STM32H743 had this change of ADC clock divisor messing up both binary and source level compatibility going to REV V. In some very rare/unlucky cases, it couldn't be worked around in software at all, rendering parts inoperable. But you can't order the old or new revision anywhere, you need to order the part number which stays the same, see what product you happen to get, then design the product around this. So shit like this sometimes happens.

author: errorprone
author_rank: Contributor
timestamp: June 19, 2021, 04:41:34 pm
content: It also depends on the manufacturer. For the i.mxrt series the silicon revision is also tacked on to the part number. Unfortunately nothing is consistent and you just have to read the datasheets and errata.

author: westfw
author_rank: Super Contributor
timestamp: June 20, 2021, 10:54:01 pm
content: QuoteMy point is that they ARE mixed up; some vendors will put them in the part number, and some won't.

author: JPortici
author_rank: Super Contributor
timestamp: June 22, 2021, 03:45:41 pm
content: Quote from: westfw on June 20, 2021, 10:54:01 pmlike TI and their LDOs that apparently have logic so complex they need different silicon revisions because safe modes are nonfunctional, and they will happily use an "A" for both a different version and a different pinout.. TPS709A is first revision, pinout A. TPS709AB is second revision, pinout B. TPS709BA is third revision, pinout A. With also a multitude of other letters after to complete the shitshow, the wrong revision/pinout can slip(I don't remember if it was actually with the TPS709 that i had these issues, but you get the point)

author: Siwastaja
author_rank: Super Contributor
timestamp: June 22, 2021, 04:40:27 pm
content: Quote from: JPortici on June 22, 2021, 03:45:41 pmOh that sucks but it's totally manageable, all you need to do is to stupidly treat the part number as an identifier for a part, each unique part number is an unique part, bypassing all assumptions and all generic wisdom about similar numbers. The longer the part number is the easier it gets since it overwhelms your brain and makes you not look at it, only copy-paste. When ordering though be very careful you are actually getting what you copypasted in the search box.But ST doesn't include the silicon revision in the part number, and silicon revisions are not necessarily binary or even source level compatible, and no, this isn't due to just bugfixes but other changes too, like arbitrarily adding a fixed, unnecessary and un-bypassable /2 clock divider into the ADC. There simplyis no processto overcome this as far as I know, unless the process is:* Every week or so, download the full st.com and all documentation, store in your archive* Very early in design, order parts for the whole expected batch of the product* Open the physical package* Look at the device markings* Now from your archive, find the documentation for that revision, since it's not publicly available anymore even though distributors sell you those parts* Now design!* Manufacture all units at once... although I'm sure if you were a large enough player like a big automotive customer ST would help you in this process, I'm pretty sure.

author: AndreZheng
author_rank: Contributor
timestamp: June 23, 2021, 05:26:07 am
content: Normally, the datasheet will lists all the differences applied on revision B. And another hidden fact is there might be some cost saving technicians also applied on revision B.

author: luiHS
author_rank: Frequent Contributor
timestamp: June 25, 2021, 12:19:14 am
content: I have been reviewing the manufacturer's errata documentation, and I see that between version A and B, practically all the errata are kept in version B, except for one that is no longer in revision B.In the document I see that almost all these errata are given solutions by software, that is, they are not corrected in the Silicon of the next revision of the chip, but it is the user who must solve it by software in his program according to the suggestions of this errata document.So I do not see that it is so important to buy a revision A instead of a B, mainly because of the A there is stock in my country, and of the B I would have to access the Chinese market, with the risk that they will sell me product counterfeit or reused, which already happened to me with some MOSFETs and accelerometers.Is it common that many errors are not corrected by hardware in the next revision of the chip, and the manufacturer simply suggests fixes by software in the errata document?

author: ataradov
author_rank: Super Contributor
timestamp: June 25, 2021, 12:30:48 am
content: Quote from: luiHS on June 25, 2021, 12:19:14 amYes, very common. Often things are not fixed even if there is no workaround.All erratas are weighted against the risk of introducing new errors. If the feature with an issue is not critical for majority of the customers, it may have erratas that are never fixed.

author: SiliconWizard
author_rank: Super Contributor
timestamp: June 25, 2021, 12:35:01 am
content: Quote from: ataradov on June 25, 2021, 12:30:48 amYes. Also, what is considered is how effective the workarounds are. If they are indeed effective, there is little incentive to correct the hardware, as not only could it introduce new problems as you said, but it could require designers to handle the parts in a different way depending on silicon revision, which is a royal pain!When designers have been relying on silicon bugs and implemented workarounds for them, they don't necessarily want these bugs to be fixed. Simple as that. Unless of course the workarounds are very annoying/not 100% effective/or add significant cost.For issues that have no workaround, that could be the same: if designers have choosen a part despite of a bug with no fix, and have designed around it, then they won't care much if the problem is fixed in a later revision.That's the general problem dealing with products that have been deployed, especially on a large scale. Once they have been, offering fixes that could actually make existing designs not work anymore is a tough decision to make. One approach that some vendors use is to finally release an "upgraded" part instead of just a silicon revision; for instance, TI sometimes releases parts with an "A" suffix; they are equivalent, but usually contain a number of fixes that make them not strictly equivalent. Since that's not strictly the same part number, and they often have a significant overlap in production with the two versions, existing customers can keep buying the old version, and take time to eventually upgrade.

author: Bassman59
author_rank: Super Contributor
timestamp: July 01, 2021, 03:26:22 pm
content: Quote from: ataradov on June 25, 2021, 12:30:48 amErratais plural.Erratumis singular.Just like data and datum.So in the above, “erratas” is not correct!