Struggling to understand datasheet - Page 1
Forum section: electronics / beginners

author: samsamm777
author_rank: Contributor
timestamp: January 28, 2022, 10:17:23 am
content: Hello all,I'm working on a new project, which has an OLED display. I've used a few displays in the past, but they have all been on board 'modules'. and just exposed the I2C, vdd and gnd pins. However this time I want to go for a more 'professional' approach and use a display on ribbon tape, rather than on a board. Anyhow i'm really strugging with understanding some of the datasheet pin descriptions for the display I want to use. Notably pins 1 to 4, C2N, C2P, C1N, C1P. The description refers to Flying Boost Capacitor and Flying Inverting Capacitor. I don't really understand this, and what I should do with these pins.https://www.farnell.com/datasheets/2549011.pdfI have a reference board, which uses the same display. Pins 1 to 4 have a capacitor network along with a zener diode, but i cant quite figure out the trace routing to understand whats going on.If anyone could help me understand whats going on here it could be hugely appreciated.

author: RoGeorge
author_rank: Super Contributor
timestamp: January 28, 2022, 10:56:48 am
content: That datasheet is too brief, you need to find a more detailed one, and some application notes with a schematic diagram for typical usage.Those are pins for the charge pump (not data). You must connect the proper capacitors there, and only if your design uses the chargepump. If not, left them unconnected, as specified in the table. You'll need an example with a typical usage schematic, usually provided by the display manufacturer.At a brief search for 'MCOT064032A1V schematic pdf' I've found a slightly bigger pdf on their website:https://www.midasdisplays.com/product-explorer/oleds/cog-graphic-oleds/mcot064032a/mcot064032a1v-bihttps://www.midasdisplays.com/getattachment/5996745b-188c-4678-8dd1-c67bdddd6619/specificationThere might be more pdf files on their website, if you can not find any schematic example, write them to ask for the missing docs.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 28, 2022, 11:01:25 am
content: That's a terrible "data"sheet... Check the manufacturer:http://www.midasdisplays.com/getattachment/27daa35a-a169-4fad-9742-73676d2c9834/specification...okay, they still don't give a circuit diagram. Well that's silly.Well the SSD1306BZ is a good hint, that datasheet should have some info in it. It will also have much more than you need (how to wire it up within the panel itself), though you need to know the command interface anyway, or maybe you have a library that's already got that.The key is, OLEDs take relatively high voltage to run, more than the 3.3V you're putting into it. It needs either an external SMPS, or onboard. And that can be using an inductor, or a stack of capacitors (charge pump). It seems they've picked the latter. A charge pump works by charging the capacitors in parallel (to 3.3V), then stacking them up in series alternately, thus getting 6.6, 9.9V, etc., or other ratios depending on number of flying capacitors and how they're being connected together. A bunch of analog switches are used to do this, onboard the chip; unfortunately, quite large capacitors are required to deliver adequate power, capacitors that certain won't fit on chip. So they're wired to pins where you can connect actual components. Note that, since the charge pump is only powering its output intermittently, filtering is required, and this is why several pins say to connect a capacitor to ground. In principle, you could even draw some current off these pins for other uses, though I would guess very little current can be spared (maybe a mA?) so it's best left alone.Tim

author: samsamm777
author_rank: Contributor
timestamp: January 28, 2022, 11:11:54 am
content: Thanks for the swift replies. I have written to MIDAS to ask for further documentation, as i also was surprised at the lack of detail. But thought it was more my lack of understanding not being able to figure out how to use the device.I wasnt aware of the charge pump concep, ill read up a bit and hopefully that will be more understandable once i do.thanks

author: dmills
author_rank: Super Contributor
timestamp: January 28, 2022, 02:57:12 pm
content: Sucky display module datasheets are a universal constant, there are NO good ones.Usually you have to look at the display 'datasheet for mechanical details and to find out which pins on the driver are exposed for your use, and then the driver chip datasheet to figure out what you can actually do, and then go to the display manufacturer for a chunk of register dump that hopefully does secret sauce to get the gamma to something sane.I have never actually seen a good explanation of how the gamma registers actually work on an LCD or OLED controller.Regards, Dan.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 28, 2022, 03:38:01 pm
content: Yeah... keep in mind how they're made:Company A makes a chip, which may be public, or under NDA in which case whatever extracts we get from it are probably partial and badly written/formatted.Company B uses chip (under license if applicable), to make LCD panels -- the chip is bonded to glass or flex, all the TFT stuff is deposited on the glass and wired up, and that's a module.Finally, Company C uses the finished panel, maybe with an additional interface board or flex, or controllers, puts it on a board or module, puts up programming info, etc., and that winds up on suppliers like Digi-Key. That includes touch controllers, or more powerful graphics controllers that add a framebuffer or what have you. Or ancillary stuff like backlight controller/power converter.Panel manufacturers are all over the place, product lifetimes are often short, a few years -- so it often takes a 3rd layer to stabilize that and offer something for low quantity / long life customers. Which is how you have a $5 panel costing like $50 or something from Newhaven or etc.And companies A and B could be Taiwanese or Chinese, so their datasheets are incomprehensible for most of us, unless translated; and it might be a poor translation. Hopefully, Company C smooths over that sort of compatibility issue as well; but, well, it seems not always to be the case.Tim

author: dmills
author_rank: Super Contributor
timestamp: January 29, 2022, 12:45:09 pm
content: Oh, but company B buys the glass in from company D who periodically change the details...Horrid things to deal with.