What are good "goto" FPGA's... - Page 1
Forum section: electronics / general

author: alank2
author_rank: Super Contributor
timestamp: August 22, 2016, 12:42:55 am
content: I've been an AVR developer for a long time and there are some good "go to" models like the ATMEGA328P for example. You can do a lot with it.I've recently had my first FPGA experience with a EP2C5T144C8N development board, but a search at Digikey under their fpga category doesn't show many TQFP style parts. My question is - are there any "go to" FPGA's that are in non QFN packages that are a minimal pin count, but still quite capable. 5V is nice, but not necessary. An example is the FPGA project I've been playing around with, it can output to VGA. What would be cool is a small FPGA that I could write to from an AVR that outputs to a VGA or even a LCD that requires a constant refresh. What smaller FPGA parts do you use that might fit this criteria?

author: Korken
author_rank: Regular Contributor
timestamp: August 22, 2016, 05:59:28 am
content: I personally use one of the small Artix-7 for general testing and prototyping.The CMOD-A7 from Digilent was a really nice board for prototyping in a breadboard, though sadly no differential pairs to pins.Though as said before, they are BGA only. But you only need some Flux and hot air to solder them.

author: zappedy
author_rank: Regular Contributor
timestamp: August 22, 2016, 09:30:56 pm
content: What dev board in the <$50 range would you recommend with any of the mentioned FPGAs or others? The Chinese have some Spartan-6 boards on eBay, but also many others. I always hear you should be wary of these because of poor support, is that always a problem?The $10 EP2C5T144 boards have too few logic blocks.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: August 22, 2016, 09:38:33 pm
content: Quote from: Korken on August 22, 2016, 05:59:28 amAnd a multilayer PCB.You can often do QFP/QFN on 2 layers, but not BGA.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: August 22, 2016, 09:42:57 pm
content: Quote from: zappedy on August 22, 2016, 09:30:56 pmLattice do some very cheap, very basic breakout boards with onboard programmers.http://www.mouser.co.uk/ProductDetail/Lattice/LCMXO2-7000HE-B-EVN/?qs=%2fha2pyFaduiPIGriJQzO%252bP1xu9A%2f0H8aSB%2flpUoOj%2f0Xd1eez49UkyjBKwlIn0DmA nice thing about XO2 is onboard flash and voltage regulator, so minimal support components needed. Single supply makes 2-layer designs very viable.

author: JoeN
author_rank: Frequent Contributor
timestamp: August 22, 2016, 09:44:20 pm
content: Quote from: mikeselectricstuff on August 22, 2016, 09:38:33 pmI just had an odd thought. One problem with routing BGAs is that you can easily use up 4 layers just for signals, even from small BGAs. But many PCB prototype houses now do 4 layer at reasonable cost. However, the general guideline is to use the two inner layers as ground and power. What do you think of using just part of the inner layers as routing to break out the BGA traces and keep the rest (say 80% or more) for the planes? Is that a purely stupid idea or might it work out?

author: hasithvm
author_rank: Contributor
timestamp: August 22, 2016, 09:46:05 pm
content: Quote from: zappedy on August 22, 2016, 09:30:56 pmTry the LatticeSemi iCEStick boards?http://www.digikey.ca/short/3h7dzr$25 USD/$35 CAD from Digikey, and they have a reasonable I/O count and a decent-ish toolchain.My goto is an old Nexys2 board I had to buy as part of a lab kit. All the IO, and enough switches and LEDs to work things out. You can probably find one on fleabay if you look enough.

author: zappedy
author_rank: Regular Contributor
timestamp: August 22, 2016, 10:15:20 pm
content: On paper that ICEStick doesn't look alot more powerful than the $10 EP2C5T144 boards? Same ballpark LE's, RAM, I/O etc.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: August 22, 2016, 10:16:46 pm
content: Quote from: JoeN on August 22, 2016, 09:44:20 pmProbably depends on where the power & ground pins actually are, and how many signal balls you actually want to use. As long as the plane comes together in the middle rather than being split into 2 or more pieces it shouldn't be a problem.I've sometimes done inner layers as signal layers with pours instead of complete planes.

author: bgm
author_rank: Unknown
timestamp: August 22, 2016, 10:18:14 pm
content: Quote from: JoeN on August 22, 2016, 09:44:20 pmIt isn't that stupid an idea and it's what I have had to do for the smaller BGA packages on a 4 layer board. Yes it does work and you can fan stuff out modernly successfully, but dealing with BGA is generally a major pain in the arse on anything less than 6 layers (at least for the higher density, larger pin count packages).Look, I will be really honest here ... I *despise* BGA to the point of it now bordering on an semi-irrational hatred, but this is to do with the fact that I work in the world of industrials and there is no single package that has caused me more pain, grief, misery and suffering when it comes to devices in high vibration environments than BGA (no ... it isn't bad package ... it's f****king awful ... QFN is *marginally* better but again ... in high vibration environments ... yeah ... still not a real good choice - I won' go into the hows and whys here - that would demand a response that would be akin to reading "War and Peace").BGA (and QFN for that matter) really is a consumer package (which statistically covers 95% of their market) and for that purpose, is perfectly reasonable.(Think of the "Major Darling" eye twitch in Black Adder ... that will give you some idea as to the effect that BGA has on me...)/BGM

author: Sal Ammoniac
author_rank: Super Contributor
timestamp: August 22, 2016, 11:15:06 pm
content: Quote from: bgm on August 22, 2016, 10:18:14 pmWhat is a good package for high vibration environments?

author: ConKbot
author_rank: Super Contributor
timestamp: August 23, 2016, 04:55:10 pm
content: Quote from: bgm on August 22, 2016, 10:18:14 pmhttp://www.microsemi.com/index.php?option=com_docman&task=doc_download&gid=130006Have you met my friend, Multi-row QFN?

author: voltsandjolts
author_rank: Unknown
timestamp: August 24, 2016, 07:03:32 am
content: Quote from: ConKbot on August 23, 2016, 04:55:10 pm

author: bgm
author_rank: Unknown
timestamp: August 30, 2016, 10:04:50 am
content: Quote from: Sal Ammoniac on August 22, 2016, 11:15:06 pmIn terms of *ease* of maintenance ... you can't go past old school through-hole DIP with soldered (not socketed) pins. The problem though is that it's a package that is nearly extinct.That leads to my *personal* preference which is QFP. The reasons for this is that soldering the leads is easily done with a simple iron, inspection is dead easy and removal of a dead component is also relatively straight forward as well.With BGA, once the component is down, you simply cannot easily inspect it in the field, and I can tell you nothing drives you nuts more than being out in the middle of scorching hot day in the mid 40s (c) underneath the blazing sun and trying to work out why a controller has suddenly started acting 'funky' because a BGA pad has cracked.QFN is better than BGA in that you can more easily 'inspect' connections and replace wholesale components a lot more easily in the field, but it is far more prone to cracking of the joints in high vibration environments.At this point, I must disclose that my personal opinions are based on regularly working in locations where you are a 15 hour drive from the closest town (all of a few hundred people) and it simply isn't feasible to drag a reflow oven or even a good rework station around, so as a result you very quickly gravitate to packages which are easily tested, inspected and replaced./BGM

author: bgm
author_rank: Unknown
timestamp: August 30, 2016, 10:09:57 am
content: Quote from: blueskull on August 24, 2016, 07:10:15 amI laughed so much at this, I damned nearly hurt myself. I can *so* relate to this kind of sentiment ....

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: August 30, 2016, 10:18:31 am
content: Quote from: bgm on August 30, 2016, 10:04:50 amSurely in that sort of environment, board exchange would be the most practical repair strategy

author: Bassman59
author_rank: Super Contributor
timestamp: August 30, 2016, 03:49:49 pm
content: Quote from: Sal Ammoniac on August 22, 2016, 11:15:06 pmThe Column Grid Array, which you'll find only on space-qualified or mil-spec devices.It has the same footprint as a BGA, but rather than solder balls, it uses little solder columns around tiny springs of wire for each pin.

author: bgm
author_rank: Unknown
timestamp: August 30, 2016, 10:40:41 pm
content: Quote from: mikeselectricstuff on August 30, 2016, 10:18:31 amFrom a practical perspective I agree ... switching out a control board is easier, but when you often have to discover exactly what you are dealing with when you are out there ... yeah ... not really that practical.There is just so *many* different boards that keeping a separate one for all just isn't feasible. If I could cart around an entire warehouse of replacement boards, then that would be the way to go, but it's simply not practical - and it's not like I can just phone someone up and the next day I get a part ... it just doesn't work like that (unfortunately).I'm dealing with basically two schools of stuff.There is the old school stuff which is kinda nice to work with (I'm talking Z80s, 6800s, 6502s, etc) and does lend itself to repair very easily, and for most part, most of that old stuff is pretty damned bullet proof. How you see that stuff being abused and it still works just *never* ceases to amaze me. It's worth fixing as ... well ... a lot of it is 30+ years old, yet it *still* works for most part and it's usually electrolytic caps that are usually the most common fault. The electronics in them is pretty damned robust (74 logic such as the 245s being the most other common fault). You will occasionally see the odd dead VIA/PIA (6522/6521/6821) but it's usually the buffers and latches that die first. Actually, I tell a lie in that regard ... the electro-mechanical relays are also another really common fault but they're usually on a separate board, and I keep a stack of those on hand (it's a really common fault).It's the newer stuff that is more 'fickle' and that is where the pain, misery and suffering really begins. My personal bugbear is the more recent controllers on the market which, despite being called 'industrial', really are just a cheap china made crap board. They are truly *horrible*.If you compare those with say a name brand such as Siemens, there is simply no comparison ... the whole quality of their construction is just *so* much better ... a 2-2.5mm board thickness, at least 10mil tracks on pretty much everything, QFP and a good coating on everything and where they use electrolytic caps, they use radial ones that are also epoxy'd down as well, so that vibration doesn't kill the caps as easily.So many of these newer 'cheap' controllers that you get these days ... despite being called 'industrial' are just *rubbish*, yet despite the mines paying top dollar for a crusher (a mine might pay $150k for say an impact crusher and yet on the side, the manufacturer of the crusher will still insist on sticking on the nastiest, cheapest, piece-of-crap controller you can get that will barely see out the warranty). Naturally, if it does last the minimal warranty period, when it does break, they charge a fortune to replace same said ultra crappy controller, and when you see how badly some of these things are made, you just have to shake your head.Most common faults I've found to date (in no particular order):* Cracked BGA joints* Electrolytic caps tearing* Board trace lifting and tearing (yes ... I've seen traces actually *lift* from the PCB - no soldering involved here ... the construction really is *that* bad)* SMD parts literally 'falling off'* Voltage regulators lacking heat sinks and left flapping around in the breeze* ... and on the newer ones, the power control ICs (seeing as a lot of the newer stuff is trying to be low power, which just makes me laugh hysterically as these things typically control 200+HP electric motors and the amount of power that a standard 5v @ 2 A controller is going to be using relative to a electric motor that size is so statistically insignificant that you wonder why the hell they bother).... and my #1 all time favourite ... tantalum caps, which, when they fail, fail short - that's just plain *evil*. When they blow, I've seen them take out traces. May the inventor of those things suffer the fleas of a thousand cats in their genitals./BGM

author: bgm
author_rank: Unknown
timestamp: August 31, 2016, 12:16:40 am
content: Quote from: Bassman59 on August 30, 2016, 03:49:49 pmI think he was referring to something that us 'mere mortals' can afford.You certainly won't be finding your garden variety $2 8051 based micro in that sort sort of package or even probably a $10 CPLD/FPGA in that sort of package - for that you need to add a few zeros to the end of your component cost..../BGM

author: Muxr
author_rank: Super Contributor
timestamp: August 31, 2016, 01:21:57 am
content: Quote from: blueskull on August 22, 2016, 12:54:02 amReally? I find TQFP miles easier.. for one if you have a solder bridge short you can simply just wick it off.. with QFP you have to remove it and solder it again, not to mention you can't visually inspect the solder joints since they are under the package, still much better than BGA.I was recently working with a LFCSP-16 package chip, and even though it only has 16 pins I have no idea if I soldered it properly or not. I don't have an x-ray. Pins over anything else, any day.To the OPs question, I really like the Lattice MachXO2, they are easy to work with, you can flash them 10s of thousands of times and are pretty cheap and available in small quantities.

author: andy1
author_rank: Contributor
timestamp: August 31, 2016, 05:42:31 am
content: I also like the MachXO2 and have used it in several projects for work and personal as it is relatively cheap, has enough memory and logic density for anything I need and package choices work nicely with 2 layer designs (qfn and tqfp for me, really wishing the qfn84 4000 part would be in normal circulation)Also the HC-parts single 3.3V power supply makes routing etc. Much easier as 99% of my designs are with 3.3v digital section.The internal flash is also convenient as it can be flashed many times and no need for external spi-flash.Small bonus is also that the manufacturer provided software supports cheap ft2232 interfaces for programming so no need to buy any specific fpga programmer.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: August 31, 2016, 07:42:33 am
content: Quote from: Muxr on August 31, 2016, 01:21:57 amThe trick with QFN is to make sure the pads extend at least 0.5mm from the edge of the package. You can then see whether or not there are solder fillets, and you can easily deal with shorts and resolder individual pins ( need 0.3mm solder).A big advantage, especially for production, is they don't suffer from bent pins like QFPs can - a lifted QFP pin can be very hard to spot.The only downside is where the QFN requires the centre pad to be soldered, as this reduces available routing area.With hot air, I find QFNs quicker to replace then QFPs as the pull onto the pads much more readily

author: Muxr
author_rank: Super Contributor
timestamp: August 31, 2016, 04:01:41 pm
content: Quote from: mikeselectricstuff on August 31, 2016, 07:42:33 amHmm.. interesting. I think my problem might be the fact that I don't order a stencil for my prototypes. I usually just dab some solder paste on the pads with a toothpick. This is why I sometimes get solder bridges. Should probably use stencils more often. Will give QFN another chance.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: August 31, 2016, 04:27:25 pm
content: For doing QFNs without a stencil I wouldn't use paste - just flux, drag a bead of solder onto each pads, flux again on pads and QFN, then reflow with hot air

author: Muxr
author_rank: Super Contributor
timestamp: August 31, 2016, 05:39:52 pm
content: Quote from: mikeselectricstuff on August 31, 2016, 04:27:25 pmThanks Mike! That does look much easier.. will give it a try, cheers!

author: JoeN
author_rank: Frequent Contributor
timestamp: September 04, 2016, 09:35:46 am
content: Quote from: Muxr on August 31, 2016, 04:01:41 pmFor QFN's what I do is put flux on the pads for the QFN footprint on the PCB, tin the pads with a chisel tip, not too much, especially for the center pad, reflux the tinned pads, flux the bottom of the IC, position the IC on the pads, and gently bring it up to solder melting temp with a hot air gun, push it back and forth to watch surface tension pull the IC into place, and then stop, clean it up, and look at it under the microscope. Never had to deal with stencils or solder paste. Anyone else go this way? It works for me.