Evil IC's stories - Page 1
Forum section: electronics / projects

author: dmg
author_rank: Regular Contributor
timestamp: February 18, 2016, 09:05:44 pm
content: I thought about opening a thread to talk about evil IC's we've found, considering evil any chip that either falis too much, always gets unexpectedly wiped from the market, has gotchas ambiguously documented in the datasheet or some other quirks that have ruined your day. I have two:1st is RF3827, a low noise RF amplifier. Turns out its bias circuit looks like a bidirectional hard short to multimeters or continuity testers in general. First time I prototyped it I checked for shorts and thought my the power rail was shorted. No obvious short seen with the microscope so I started removing components from the board until I removed the amplifier, short gone, replace, short, check pinout and it's right, damn the amp must be broken or shorted inside, get new one, short, WTF? Power up, all is right, wtf? ... At least I learned about biasing topologies while investigating this issue.-TXS02612. This little bastard is an innocent looking sdcard interface SPDT switch with bidirectional voltage translator that I've seen implemented in several designs as level translator only. It's one of the only active sd translators out there that's available in something that's not BGA. All those designs spent at least a PCB revision fixing issues with sdcard because of it. The gotcha? At least one of them is a note at the top of datasheet's page 15, right after all interesting stuff has been said, just before packaging and other information. The note says that you "should" power-sequence the device, applying power in a three-step process, and if you don't shit might not bias properly and direction sensing might not work or other funny stuff might happen. That "should" should be a "MUST" written in big red letters at the first page of the datasheet, because it gets you very hard and it's random, some batches are more sensitive than others to this issue. Also, if you follow the rules perfectly some SD card brands just refuse to work with it. It has gotten me recently...

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 18, 2016, 09:51:52 pm
content: FT232RQ -- package and footprint reads like a QFN. It's not, it's actually an LGA arranged like a QFN.I didn't have to work with it, but I've worked on a project that suffered from it: a Vinculum USB and uC core, from whoever the hell makes it. Apparently it's *awful*.I'm sure I've seen or used other things that I've repressed for good reason...Tim

author: os40la
author_rank: Regular Contributor
timestamp: February 18, 2016, 10:18:35 pm
content: What about this evil IC?

author: retrolefty
author_rank: Super Contributor
timestamp: February 19, 2016, 12:50:59 am
content: QuoteBut don't you know that the 'real engineers' don't get to work on the cover page of datasheets, that's the marketing departments sand box.

author: Monkeh
author_rank: Super Contributor
timestamp: February 19, 2016, 12:58:52 am
content: Quote from: T3sl4co1l on February 18, 2016, 09:51:52 pmWTF? And I thought their weird wide TSSOP-20 was bad enough.QuoteFTDI..

author: daqq
author_rank: Super Contributor
timestamp: February 19, 2016, 08:07:39 am
content: The STR9x (and various other ones) series of MCUs from ST... though I'm sure MANY suffer from something similar. Lets say you have the MII or RMII or external memory interface on a TQFP package. Now, how do you group your pins? Together? Apparently not - the best way is to have an interface of 16 pins occupy 3 different sides of a giant package, intermixed with other interfaces, power, crystal oscillator, because why not? I mean, would it make baby Jesus cry if they put the pin functions together so that you do not end up with a via minefield?

author: AndyC_772
author_rank: Super Contributor
timestamp: February 19, 2016, 08:30:18 am
content: I nominate the Micrel Ethernet switch IC, which has pins on it that are marked in the data sheet as LED outputs.Only, they're not. They're 'LED Out / undocumented factory test configuration In', which means if you're using them to drive a transistor instead of directly connecting an LED, they're sampled as 0 at reset, instead of 1.The symptom of this? A couple of ports don't work. Good luck finding that one.I'd also like to nominate the old SCSA interface chip whose data sheet gave package dimensions in both imperial and metric units... that weren't the same. Design a PCB using the wrong set of dimensions, and the chip doesn't fit. We had to splay out its legs (about 100 of them) to make them fit the prototype boards. Fun.Then there's the engineering sample IC which worked fine, apart from the bug in the I/O ring which meant its input logic '1' level was about 0.4V.Also burned into a special part of my brain, is the SDRAM interface on the old Freescale PowerQUICC processors. They'll talk to SDRAM, but you have to create a program that describes the timing of every address / data line and strobe using a look-up table called the Universal Programmable Machine. I cannot describe just what a loathsome experience this is... and if you get it slightly wrong, then some device will fail with occasional, random memory errors, under some conditions, somewhere. Believe me when I say DDR in all its incarnations is a hundred times easier.

author: tom66
author_rank: Super Contributor
timestamp: February 19, 2016, 09:34:36 am
content: Not strictly the chip's fault, but we had a transistor almost kill/maim one of us at work. It was a D2PAK device as part of a moderate power motor controller (around 250W at 60VDC) and we were testing it without the heatsink running under light load from a lead-acid battery bank. For some reason or another the driver IC on the low side decided 100% duty cycle was a good idea, causing the lower FET to switch on permanently, detonating it off the PCB and ejecting it into the ceiling tile above as the entire short circuit current of the battery was placed through a small MOSFET.To this date, there is still a mark in the ceiling tile showing where the transistor attempted to enter low-earth orbit.

author: dmills
author_rank: Super Contributor
timestamp: February 19, 2016, 11:41:12 am
content: Opamp datasheets that do not mention correlated noise due to bias current cancellation schemes, can be noisier then you expect unless you are very careful.Altera FPGAs with a small note on page 1167 of the datasheet to the effect that even if not using the code security stuff the thing will not come out of reset unless the battery terminal is powered (And it is not a ball you can get to after the fact).Then we have the wonder of parts where the controlling dimension is metric, but everything seems to be on a 1.27mm grid, somebody does not quite get it.Can I also offer an honourable mention for anything where the datasheet gives a 'required value' rather then a range, Ethernet PHY bias resistors, looking at you! 2.67k might be ideal, but knowing if anything from 1.8k - 3.3k would work, would be really helpful and might save be a single use part on the BOM, recent TI has been annoying this way.App note BOMs that are wrong are evil, TI has a eval board for the TAS5715 where the BOM gives a cap value for a snubber that is about two orders of magnitude too big, if you are not paying attention your direct copy of the design melts the snubber resistors...Regards, Dan.

author: plazma
author_rank: Frequent Contributor
timestamp: February 19, 2016, 12:26:05 pm
content: AD5316R used to have a datasheet error which resulted to Vdd being almost in short to ground.The datasheet used to say:RSTSEL Power-On Reset Pin. When this pin is tied to GND, all four DACs are powered up to zero scale.When this pin is tied toVDD, all four DACs are powered up to midscale.Now it is fixed:RSTSEL Power-On Reset Pin. When this pin is tied to GND, all four DACs are powered up to zero scale.When this pin is tied toVLOGIC, all four DACs are powered up to midscale.It was easy to find the hot component but it took a while to find the fault since the datasheet was wrong. Analog support found the fault after we supplied part of the schematics.

author: ovnr
author_rank: Frequent Contributor
timestamp: February 19, 2016, 12:39:09 pm
content: STCF07 high power buck-boost LED driver.Datasheet says "an optional NTC resistor protects against overheats". Yes, and if you simply leave the NTC pin disconnected, it won't start up. Absolutely hilarious to bodge wires onto a 4x4 0.5mm pitch QFN on a tiny-ass board.

author: ajb
author_rank: Super Contributor
timestamp: February 19, 2016, 01:03:31 pm
content: Quote from: dmills on February 19, 2016, 11:41:12 amTI also has a split rail switcher calculator spread sheet that will tell you that the output caps should be e.g. 30uF on the positive side and 0.1Fon the negative. Turns out what's labeled 'Cneg' is actually the negative cap's ESR. At least it's wrong enough to be blatantly obvious...

author: exe
author_rank: Unknown
timestamp: February 19, 2016, 01:54:41 pm
content: Quote from: daqq on February 19, 2016, 08:07:39 amWhy, WHY are they doing this? I have exact problem with interfacing a 16bit display bus. My only guess is that they try to keep pinout in somewhat common across different packages. Say, the pinout of qfn-32 looks similar to qfn-64 (though the latter additional IO ports available).

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 19, 2016, 07:19:50 pm
content: I've personally laid out STM32F4 and ATSAM3 MCUs that have the ports in randomized nibbles. It's a pain in the ass.Remembered another one, from sci.electronics.design: AD7793https://groups.google.com/forum/message/raw?msg=sci.electronics.design/qvGBxlsC23M/lw4SJMNfEQAJQuoteTim

author: tszaboo
author_rank: Super Contributor
timestamp: February 19, 2016, 09:18:55 pm
content: Every single analog switch. How it looks on the pcb: Signals come from left, swiched, go to the right.How the package looks like? Lets have the signals on all edge, mix them with noisy digital signals, and add the power in the middle.I'm sure it made a lot of sense to the IC designer. And then of course they behave like bad puppies.

author: wraper
author_rank: Unknown
timestamp: February 19, 2016, 09:48:41 pm
content: https://www.eevblog.com/forum/projects/are-there-different-versions-of-the-worldsemi-ws2803s/

author: tesla500
author_rank: Regular Contributor
timestamp: February 19, 2016, 11:00:13 pm
content: Quote from: NANDBlog on February 19, 2016, 09:18:55 pmPinouts are probably dictated by the layout of the die. whatever the order the pins are on the edge of the die, that's what they are in the package, at least for leadframe parts. I wonder why they can't just use the bondwires as jumpers to reorder the pins slightly though.Power pins in the middle makes sense from an inductance perspective, smallest distance from pin to die. On wide packages the extra length can be quite significant.

author: JJalling
author_rank: Unknown
timestamp: February 19, 2016, 11:23:22 pm
content: SHT11 from Sensirion. Why the heck put a dot next to the NC pin instead of pin 1. And why the heck don't they place pin 1 in the top left corner???I think they are testing if people are reading the datasheet or not - they got me :-/BR Jonas

author: Cerebus
author_rank: Super Contributor
timestamp: February 20, 2016, 12:31:33 am
content: Quote from: JJalling on February 19, 2016, 11:23:22 pmI think the clue is in the part number. I had a metallurgist friend at college who always claimed the standard alloy number for mild steel was SH-one-T.

author: daqq
author_rank: Super Contributor
timestamp: February 24, 2016, 07:21:20 am
content: Yesterday I got bitten by two minor notes in LT datasheet and one incongruity in the simulation model in LTSpice.First off the LT1112:Quote...so, no voltage clippers. The simulation model does not model this part of the behavior, I have already reported it.Then there is a creative SPI implementation in the LTC2601, namely the SDO output.QuoteSo, some surgery was required since it was blocking the bus.

author: MrSlack
author_rank: Frequent Contributor
timestamp: February 24, 2016, 09:11:36 am
content: I wrote a driver for a realtek Ethernet controller once. Think it was the 8139. NOTHING in the datasheet was true and most of the facts were derived from reading the freebsd and Linux kernel sources which were full of bitching about it too.

author: jeroen74
author_rank: Frequent Contributor
timestamp: February 24, 2016, 12:14:02 pm
content: Order of pins on this sensor:http://www.microesystems.com/products-services/linear-encoders-nano/m1200

author: poorchava
author_rank: Super Contributor
timestamp: February 24, 2016, 12:32:12 pm
content: SPIRIT1 sub-1GHz transceiver chip from ST. It has some pretty clever logic inside and this includes 96-byte long FIFOs for RX and TX. You can set stuff to happen when number of elements exceeds 'X'. Too bad that for RX FIFO this is actually a number of bytes left, not bytes used... And they only marked it one one picture in entire datasheet.... Took us like 2 or 3 days to figure this out...

author: dfmischler
author_rank: Frequent Contributor
timestamp: February 24, 2016, 01:41:11 pm
content: Quote from: MrSlack on February 24, 2016, 09:11:36 amSame here. You couldn't possibly write working code for that chip if you believed the datasheet.

author: Artlav
author_rank: Frequent Contributor
timestamp: February 24, 2016, 01:49:59 pm
content: Altera Cyclone IV FPGA, EP4CE10E22.The package have an exposed pad, which is not for thermal reasons, but MUST be connected to the ground plane properly.Otherwise the thing won't program at all, despite the pad being internally connected to the ground pins.I did not anticipate that, and so was forced to do full-blown reflow soldering (DIY setting here) of the chip to get it to connect...On a dozen boards.

author: AndyC_772
author_rank: Super Contributor
timestamp: February 24, 2016, 02:39:28 pm
content: Tip: on that same device, did you spot that the MSEL pins must be connected toanalogueVCC for a logic 1, ie. 2.5V, and not one of the I/O banks' digital supplies?

author: Jeroen3
author_rank: Super Contributor
timestamp: February 24, 2016, 04:53:48 pm
content: Somewhere on this planet, there is a lqfp molding machine that leaves 2 injection marks and 1 pin 1 circle.This is pure evil when it is not shown on the datasheet. And when the datasheet does not show the texts.You'll have to find pin 1 from the tape/tray orientation. If you got it in tape/tray.

author: Messtechniker
author_rank: Frequent Contributor
timestamp: February 25, 2016, 06:11:18 am
content: Not ICs but transistors instead.Going back some 40 years and hard pressed for money (student, you know), I purchased 100 special offer BC 337 NPNs made in the GDR (our German communist friends at the time). And a very special offer it was! After finding out the hard way that they would not work – being made in GDR I did not expect much anyway – I then after a while found these buggers to actually be some sort of PNP silicon with a bit of beta. If not too strict about specs they could have been labelled BC 327 perhaps. Lucky for the offender to be behind the iron curtain as otherwise I would have stuck my hot soldering iron….<heavily censored>.Since at that time I used to hang out at a mayor Cologne radio station, I traded the lot in for some blank tape.The teaching staff of the broadcasting training unit then used these trannies in the course of component level troubleshooting exams making the students really sweat, as you can imagine.

author: Ice-Tea
author_rank: Super Contributor
timestamp: February 25, 2016, 08:27:28 am
content: A DSL chipset of a manufacturer that shall remain unnamed (they have more lawyers than me). It had a 1.2V core voltage with tight tolerances (+/- %), the 1.2V was regulated by an integrated buck regulator. In the field, some units started to reboot. Only a very small percentage, but enough to make the end customer complain. At first, it looked like even when a very small noise peak ventured below the -3% threshold, the unit would reboot. A while later we found units rebootingwithoutviolating the 3%.To add injury to insult: the IC manu's FAE go involved (obviously). At some point, we figured out that the tolerance of the internal voltage reference came into play (if it's 2% low, you have 1% margin remaining on your board, not very comfortable). So the FAE dialed in the actual chip design engineer (yes, the project wasthatbig. So, he was asked what the actual tolerance was on the reference. He innocently replied "+/- 3%". At which point I was speechless and the FAE nearly fell off his chair "that leavesnonoise margin on the board"! The design engineer seemed a bit confused at this point, as if he never even considered this.

author: Artlav
author_rank: Frequent Contributor
timestamp: February 25, 2016, 11:01:01 am
content: Quote from: AndyC_772 on February 24, 2016, 02:39:28 pmYep.It was mentioned in the middle of one of several "how to wire this chip" documents.More of luck, really - this was rather new to me, so i read through every one of them and paid attention to most of the notes.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 25, 2016, 11:45:38 pm
content: Quote from: Ice-Tea on February 25, 2016, 08:27:28 amAnother favorite-to-hate from the newsgroup: there's a DSL line driver (analog buffer) that claims +/-15V supplies, but is only good for a 5V output range. ...Bad...things happen when you try to use it for a more obvious range. Like latchup and overheating.A pet peeve of mine: synchronous buck converters should be timed for an interference condition, rather than open-circuit dead time (that is, ~30ns of shorting time is better than 30ns of open time). Why? Because you snub that with an RLD network in series with the high side switch, and all is fine. You can't fix dead time, which inevitably causes forward bias of the low side body diode, leading to increased losses and EMI.One of the LT uModule bricks does this; it gives off <2ns spikes with amplitude equal or greater than the supply voltage (I didn't have a scope handy that was fast enough to resolve it). Likewise, the LTC3810 suggests an impossibly wimpy diode in parallel with the low side switch, which does fuck all. Fortunately, those projects went inside metal boxes, and I was able to filter it good enough to pass...More notably, a TI/National monolithic regulator part (I don't remember what, offhand; this example is also from the NG) has just enough dead time to forward bias its low-side body diode, then yank it off (hard recovery), resulting in, not just high peak currents, but evidently a true drift step recovery mode, resulting in fractional ns risetime!Switching design, in general, utterly rejects even the barest possibility of supply inductance. Monolithic regulators could have separate logic and switch VCC pins, but they don't, so you have no choice but to heavily bypass them. You at least have the option, when external-switch circuits are used, but no one talks about snubbing those, either (and you never have the option of being able to adjust timing to allow overlapping drive). The app notes, dev kits and FAEs (even from a company as rich as Linear) are utterly useless and ignorant of EMC issues; at best, they'll tell you to throw some ferrite beads on the supplies, which is ineffective at best (they saturate), and completely misses the fundamental source of the problem, which they've unintentionally optimized to be as bad as possible in the process.Tim

author: poorchava
author_rank: Super Contributor
timestamp: February 26, 2016, 12:37:48 am
content: There is a range of dsPIC30 devices, which need exactly 7.5MHz crystal to achieve maximum clock frequency. Other frequencies won't do because of the limited input range of the PLL. Now try get such crystal... Yes they are out there but they are hard to get, especially for a hobby project. I wonder what the chip designers were thinking...Another one: a low power integrated SMPS chip from TI, which is normally meant for buck operation, but can also work as an inverting buck-boost which is described in an application note... Too bad that in our application it wouldn't start oscillating in some cases.... unless one shorted the output cap with a tweezer or something. Nobody seemed to have any clue WTF: support forums, FAE, nobody. Spice model doesn't work for this mode of operation... Cool...

author: manu
author_rank: Regular Contributor
timestamp: February 26, 2016, 10:42:16 am
content: Quote from: T3sl4co1l on February 19, 2016, 07:19:50 pmHad to deal with this one. Nightmare.

author: vk6zgo
author_rank: Super Contributor
timestamp: February 28, 2016, 05:32:35 am
content: Some years back,I was modifying an "in House" constructed Transmitter Remote control,The mod went OK,but when I was messing around,I removed a couple of 4000 series monostables,which were used to obtain several fairly long delays.Oops--I lost one.No problem,just grab a new one from the store!Plugged in and tested-----the thing "timed out" after a way too short a delay.Weird!----Must be a faulty one!Tried another one with the same result.When I tried the old one from the other position,it operated correctly.!!A bit of research revealed that NS had decided to split the range,keeping the old number for monos which were optimised for short "on" times,& creating another number for circuits requiring long "on" times.We bought some of the "long time" type,& they worked perfectly.The next job was to either replace every one we used,or to document the situation --we chose to do the latter.

author: MrSlack
author_rank: Frequent Contributor
timestamp: February 28, 2016, 09:28:30 am
content: That sounds about right. If there's one thing I've learned over the years, 4000 series are dicks. I've had a couple of completely unintuitive half working ones over the years, particularly the 4046 PLL leading to much head scratching. Also they're actually very different between vendors as well with respect to input and output protection and this can have some significant side effects on some analogue circuits which shaft you if you replace say a 1970s RCA device with a modern TI device. Still use the things though!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 28, 2016, 01:06:15 pm
content: Supposedly, the original CD4046s are still the best PLLs for the frequency range. The 74HC4046 and 7046 were designed by retards: the charge pump PD has some degrees of dead time, and the oscillator is drifty and nonlinear.Tim

author: MrSlack
author_rank: Frequent Contributor
timestamp: February 28, 2016, 01:10:13 pm
content: I've only used the CD4046's myself. I have heard the same as well. RC oscillators in the 4000 series are all quite drifty generally. Tend to use an old bipolar NE555N as the master RC oscillator or an xtal on a 4060. They're quite stable. Trimmed RC for <2% accuracy. xtal for anything more accurate divided down to the frequency I need.

author: Gribo
author_rank: Frequent Contributor
timestamp: February 28, 2016, 07:52:12 pm
content: TI's MSP430F135/149 and then the MSP430F235/249 - Low power brownout detector that doesn't work when the battery's voltage drops too slowly. Had to retrofit 1K units with MAX809 to fix that.The CC1101 app note regarding FCC certification in 915MHz - No way in hell you get that spectral mask with the supplied parameters. The result? Lower link budget, just to pass certification. Their response? Ah yes, a mistake in the automated gig..