Generating multiple low current TFT LCD Power Supply Rails??......... - Page 1
Forum section: electronics / projects

author: Smokey
author_rank: Super Contributor
timestamp: October 11, 2023, 11:25:14 pm
content: I'm finding myself needing to directly interface with a TFT LCD in RGB mode. That's all fine, but I also need to power the thing.I only need a 3.3V rail for the rest of the system, so it would be great if I could cover all the following LCD rails starting from that:(These are the specs from the display manufacturer)DVDD=3.3V at 3mAAVDD=10.4V at 17mAVGH=16V at 200uAVGL=-7V at 300uAVCOM=3.5V~4.5V at 20uAThe backlight needs 9V at 150mA, but I got that covered already.I can pick up all those LCD supply rails in one chip with the TPS65100, but that part has significantly more output capability than I actually need for this job. I haven't priced out the whole TPS65100 solution yet with all the diodes and inductor and caps and stuff.https://www.digikey.com/en/products/detail/texas-instruments/TPS65100QPWPRQ1/1950835https://www.ti.com/lit/ds/symlink/tps65100-q1.pdfConsidering the super low current requirements, what have you guys used for something like this to keep the cost down? Is the TPS65100 a good option even though it has way more capabilities than I actually need here?

author: Smokey
author_rank: Super Contributor
timestamp: October 16, 2023, 12:26:58 am
content: I think I'm just going to use the TPS65100 here. At least I'll have that circuit in my library when I need to drive a display that actually needs the higher power capabilities.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 16, 2023, 03:06:50 am
content: It doesn't have an onboard converter? I've seen at least one display that had an onboard controller and you attached external MOSFET and diodes and capacitors at the far end of the flex cable, to supply all the oddball voltages... weird, but it worked fine anyway. Let me see... ah yes, that was an e-paper display that did that exactly.They don't give a recommended circuit either?Edit: they had this suggested circuit, maybe that gives you some ideas.Tim

author: Smokey
author_rank: Super Contributor
timestamp: October 16, 2023, 04:25:44 am
content: Nothing internal but the COG LCD driver chip. All of the power supply stuff and RGB is up to me.There was not only not a recommended power supply, they didn't even give the current requirements on the datasheet. There was also no mention of what to do with the VCOM voltage at all. I had to email engineering. Without guessing it is essentially impossible to do a design using only the datasheet information. Fun times!This is another rant, but some of the industries that are almost exclusively Chinese suppliers like LCDs seem like they have the worst documentation of all time.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 16, 2023, 06:33:02 am
content: People complain about companies like Newhaven severely marking up commodity products, but so quickly forget just how much work they actually do behind the scenes. Until they have to actually do it themselves...Mind, not accusing you of such a perspective, more to say: anyone reading this, who was wondering... now you know another little piece of it.Within China itself, probably a lot of these companies make do by literally being next door to each other, and having ready contacts whether in person or over the phone (or Weibo or whatever). And I'm sure they have no shortage of frustrations themselves, but as long as a few customers figure it out well enough to sustain sales, it doesn't really matter. And so, even if we're lucky enough to get poorly translated datasheets at all, they need not be complete, or, much of anything really. Sad, but alas.I suppose maybe in time, industry/trade orgs and standards will take root over there, and doc standards will rise, but this will take time -- I imagine, coincident with everything else improving to such a point that enough people find it frustrating enough to solve, as opposed to just the day-to-day frustration of existence. In short: a middle-class sort of problem.Tim

author: Smokey
author_rank: Super Contributor
timestamp: October 16, 2023, 05:30:44 pm
content: As I've said elsewhere, I've been in charge of documentation before, so I feel that pain. But I've also been in charge of tech support and I can say for sure that those two things have a direct relationship.As a tech support person, I can absolutely guarantee that you will need to answer the same question over and over and over and over again, until the point that you finally revise your documentation and include the information that people keep asking about.There will be people that still won't read the documentation and still ask the same question, but at least now you can shame them for not reading the documentation when you answer it.

author: Buriedcode
author_rank: Super Contributor
timestamp: October 18, 2023, 06:14:11 pm
content: Perhaps I'm missing something, but why not just a single boost converter powering multiple opamps with resistive dividers for the voltages? The negative one can just be a charge pump with zener - assuming the current draw is fairly consistent.edit: Considering the 10.4V is the highest current - that can be the boost coverters output. A doubler for the 16V - with zener regulation, an inverting charge pump for the -7V (another zener), and the others can just be a dual opamp powered by the 10.4V.