Cheap LED driver and cheap RGB LED quality - Page 1
Forum section: electronics / projects

author: 3dgeo
author_rank: Frequent Contributor
timestamp: November 16, 2019, 07:03:39 pm
content: Hi,I designed PCB around 16 outputTLC59116IPWR(US$1.1833), but recently I foundIS31FL3236A-QFLS2-TR, a cheap (US$0.547) 36 output IC. Currently I'm making sample PCB to test it, but I wanted to know community opinion on it.It's package is really small for 36 output @38mA (MAX), I'll be using it @5mA (may be 10mA) with RGB 3528 LEDs. Tho I'll make test PCB to test it @20mA. Also I should mention that IS31FL3236A has a very nice feature – it stores RGB values in a buffer and latches them all at once when it receives I2C commend to do so. A small disadvantage is that its max PWM is @22Khz vs 100Khz on TLC59116IPWR, but I don't think it will effect my design.Also I would like to discuss RGB led quality, due to specific reasons I will be using 3528 "regular" SMD mount RGB LEDs, but I'm noticing they are being phased out on LCSC, and on Digikey they are way too pricey. But on Ali they are incredibly cheap 1000pcs - ~4usd, I actually got few batches from ALI and they seem to have some visible light inconsistencies at low brightness.I guess my question would be what is the difference between expensive and cheap LEDs? Is expensive LEDs more consistent, brighter? Price difference is 0.4ct vs 40ct or more.If you have something related to say – say it, just wanted to get some feedback cos rerouting PCB will take at least few days, but I will be saving a lot on LED drivers (3 of them per board) in a long run if that chip turns out to be as good as it looks.Have a great day

author: SiliconWizard
author_rank: Super Contributor
timestamp: November 16, 2019, 07:09:37 pm
content: Oh, I was first thinking you'd be switching to an obscure and not well documented unknown chinese chip, but it's an ISSI chip which looks pretty decent. Thanks for pointing it out, I may have some use for this later!As to power dissipation, it has a small QFN package but of course with a thermal pad. Soldering the thermal pad and adding a few vias through the pad on PCB is definitely not optional.

author: 3dgeo
author_rank: Frequent Contributor
timestamp: November 16, 2019, 08:45:52 pm
content: It's hard for me to understand – are you being sarcastic only in 2nd part of your post or in 1st also

author: SiliconWizard
author_rank: Super Contributor
timestamp: November 16, 2019, 08:58:21 pm
content: Oh, in neither actually, for once!

author: 3dgeo
author_rank: Frequent Contributor
timestamp: November 16, 2019, 10:04:35 pm
content: So why you think vias on thermal pad is not optional? I added 5 vias.Mind sharing what your plans with this IC?Doing some LED stuff as well?

author: wraper
author_rank: Unknown
timestamp: November 16, 2019, 10:15:08 pm
content: ISSI is well known manufacturer for it's RAM and FLASH. Expensive LED does not mean bright.

author: SiliconWizard
author_rank: Super Contributor
timestamp: November 16, 2019, 10:20:52 pm
content: Quote from: 3dgeo on November 16, 2019, 10:04:35 pmThe vias will help dissipate heat (and of course distribute current) through the other connected layer(s). Ideally have at least one solid ground plane if you can.Quote from: 3dgeo on November 16, 2019, 10:04:35 pmYes, I'm thinking of making some kind of LED-based display, and I definitely want to limit the number of parts (apart from the LEDs obviously). Of course the question will be whether it's worth it compared to using like the Neopixel LEDs for instance, which can be had for pretty cheap by quantities.

author: mariush
author_rank: Super Contributor
timestamp: November 17, 2019, 12:24:23 am
content: TME.eu has 16 RGB leds in 3528 package:very long tme.eu linkThe cheapest is 6$ for 100, plus VAT :https://www.tme.eu/gb/details/rf-w7sp30ts-a44/smd-colour-leds/refond/If you don't mind other packages, they have cheaper but PLCC6 (~5050) for ~8.75$ for 250 leds :https://www.tme.eu/gb/details/rf-w2sa50ts-a39r/smd-colour-leds/refond/You should also check out IS31FL3741 - it's more expensive but it has 39 Current Sink × 9 SW matrix size: drive up to 351 LEDs or 117 RGBsHere's link to it:https://www.digikey.com/product-detail/en/issi-integrated-silicon-solution-inc/IS31FL3741-QFLS4-TR/706-1662-1-ND/9169513Here's PDF :http://www.issi.com/WW/pdf/IS31FL3741.pdfWould be good enough to make 10x10 tile, or a 12x9 (4:3 aspect ratio) - the max is 117 RGB or 13x9 rgb leds

author: 3dgeo
author_rank: Frequent Contributor
timestamp: November 17, 2019, 04:58:22 am
content: Quote from: SiliconWizard on November 16, 2019, 10:20:52 pmI think it depends what is projects current limit and how much time you willing to spend making PCB. My current limit is way beyond max led current, so If I use neopixels I have to drive them max at 25% current, that means only 25% color steps from 256, plus adding linear color correction and I would get barely a few steps from 0 to max brightness. So I have to use driver so I could still use 256 steps. But routing for regular RGB LEDs is annoying and tedious... Also there are plenty premade displays in Ali @descent price, so making one is not best use of timeQuote from: mariush on November 17, 2019, 12:24:23 amWow, thanks, that's a nice IC, it's almost what I need – I'm making 105 RGB matrix (old config 15x7, new 35x3), but it's not all that simple – price is still way more than 3 * IS31FL3236A-QFLS2-TR + using 3 ICs gives me 105 outputs vs 39 + routing for 3 chips will be way simpler than routing for 1, heat dissipation from 3 chips should be slightly better. Tho considering only price – extra 2 dual external fets and extra 4 parts to PNP should make 1 IC viable choice. Hm, that's a hard decisionI will contact LCSC and ask if they can get them, LCSC will sell them probably way cheaper than Digikey...What comes to LEDs, I'm aware I can buy them for crazy high price, it's not what I need

author: mariush
author_rank: Super Contributor
timestamp: November 17, 2019, 10:16:59 am
content: Well, for 35x3 that would work perfectly... the chip can do 13x9, so you can easily arrange them to have 36x3 and just not solder the 36th columnYou have the added advantage of 256 steps of brightness for each of those 9 channels, and a global brightness level for all channels. You can set a higher current limit through the resistor and then set the max brightness for some color channels lower because some colors are more efficient and produce more light.You also haveIS31FL3731at LCSC, at 0.9$ if you get 10 or more:https://lcsc.com/product-detail/LED-Drivers_Integrated-Silicon-Solution-IS31FL3731-QFLS2-TR_C191206.htmldatasheet here:https://datasheet.lcsc.com/szlcsc/Integrated-Silicon-Solution-ISSI-IS31FL3731-QFLS2-TR_C191206.pdfIt's a 144 led driver, arranged as 2 matrixes, each with 8x9 leds. So you could rearrange the leds as 2 groups of 24 x 3 single color leds, or 2 groups of 8 x 3 RGB leds.Ideally, you would use 3 of these chips, one for each color, because you'd want to set separate current for each red, green and blue.... but it would be a bitch to do the wire layout for a 35x3 display ... lots of traces on just two layers. Going with 4 layers would significantly reduce the PCB difficulty but what you save on led drivers, you put in the circuit board.Another driver that may be worth keeping your eyes on, isLP5036... 36 channels or 13 RGB leds:https://www.digikey.com/product-detail/en/texas-instruments/LP5036RJVR/296-LP5036RJVRCT-ND/10435072datasheet :http://www.ti.com/lit/ds/symlink/lp5036.pdfThe driver has 3 programmable banks, one for each color, and has 12bit PWM output and 8 bit global brightnessYou could arrange it as 4x3 RGB leds (12 channels) and then use microcontroller to do 1/9 duty cycle (36 columns divided by 4 columns lit at a time = 9 "areas" of 4x3 RGB leds) but this would mean you'd need 9 mosfets to switch power between "areas" and naturally a microcontroller with higher pin count, 9 extra io pins to enable or disable the mosfets.

author: 3dgeo
author_rank: Frequent Contributor
timestamp: November 17, 2019, 02:56:29 pm
content: Hm, I don't like that IS31FL3741 has 9 anodes, it's a bit too much on routing and it reduces light significantly. To get same light amount I have to drive each led @~23mA, that's not a big deal, but cheap LEDS may not like that. Also if I use only 8 anodes I would get only 104 leds instead of 105 I needAnd leaving out 3 cathodes and using all 9 anodes seems a bit wastefulBig advantage IS31FL3741 is a memory buffer for entire matrix! In my current configuration I have to send new data if I change active fet.Also there is "open detection" and "short detection" – I'm guessing it's used for key press detection?If so than's a very nice feature!IS31FL3731 – can't see myself using this chip.LP5036 – has very nice features, tho way too expensive.I will nag LCSC about IS31FL3741, if they can get it at descent price I'll role with them, otherwise IS31FL3236A.3 * IS31FL3236A I would give 35*3 + 1 extra output per chip (I'm using free outputs to reduce resistance on R_EXT and increase LED current if PSU allows it).Quote from: mariush on November 17, 2019, 10:16:59 amTell me about itI have working 2 layer PCB prototypes with 45x7 (3 ICs with 16 outputs), and it is tight..... Tho I managed to squeeze 0.3mm traces, but if my assumptions are correctwith new ICs I have room for 0.15mm at bestand some traces are 25cm long.No, my assumptions were wrong, if I use this chip routing will be at the same level or even simpler!Edit:I noticed in datasheet that IS31FL3741 has resistors on every input (20/51ohms), but no info on them. If they are required this chip is not suited for me, I don't have place for 39 resistors on the PCB, plus PNP cost will be huge...