Display LED driver IC recommendation for 16 LEDs, 40mA@26V - Page 1
Forum section: electronics / beginners

author: Mecanix
author_rank: Frequent Contributor
timestamp: August 08, 2022, 04:28:04 pm
content: Hi guys, At last, 3 weeks holiday ahead and something new (to me ) to toy with. A 5" Display!I've received the display yesterday, all looks great however I've never anticipated those needs led drivers.Can anyone of you recommend a small form format, low passive counts, LED driver IC. One you've successfully used before and think works best for the specs attached.I'm aware there are thousands out there, hard to make a choice and so that's why I'm asking around. Hopefully there is already a "go to" famous IC for this...Thanks in advance

author: Zero999
author_rank: Super Contributor
timestamp: August 08, 2022, 05:20:21 pm
content: A 28V supply and a 68R series resistor.https://www.acadaptorsrus.co.uk/genuine-flo-ac-dc-adapter-fd28vd-12-50-12v-50ma-eu-power-supply/https://www.poweradaptorsuk.co.uk/500ma-05a-28v-14w-acdc-regulated-switch-mode-power-adaptor-353-p.asp

author: mariush
author_rank: Super Contributor
timestamp: August 08, 2022, 05:59:34 pm
content: The text says 25.6v +/- 0.3v which would make sense for 8 white leds in series, like in the picture.Ideally you would use a step-up / boost led driver. Start by going to reputable distributors (digikey, mouser, newark/farnell) and search for drivers that can boost some low voltage up to 25-30v and have configurable current limit.For example, here's led drivers that can boost 3.3v (because that's same voltage the display needs so let's keep the power supply simple) to around 26v, and which can supply at least 50mA (you will set the peak current limit to 40mA or less using a resistor or something, you want drivers that won't struggle, so if they can do a bit more than 40mA that's fine) ... only those in stock and sorted by price.Digikey link :https://www.digikey.com/short/pmd9cdm4The first result is AP5725, 50 cents chip ... should work, but if you check the schematic they recommend to be used with maximum 6 leds in series.If we go down the list, PAM2841 advertises in datasheet -https://www.diodes.com/assets/Datasheets/PAM2841.pdf- that it can do 10 or more white leds in series, so 8 leds shouldn't be a problem ... and it can work with 2.75v...5vAll the examples set the current limit to 20mA by configuring R3 as a 10 ohm resistor - for 40mA you use a 5.1 ohm resistor. Personally, I'd use a 5.6 ohm resistor to set the max current somewhere around 38-39mA ...5.6 is a standard value and 1mA of current won't make much of a difference.MCP1664 would work and it's available in two footprints and datasheet is easy to follow to configure your circuit :https://ww1.microchip.com/downloads/aemDocuments/documents/OTH/ProductDocuments/DataSheets/20005408A.pdfNote the paragraph may make it seem like it's not possible to have 8 leds with 3.3v input, but scroll down to page 2 and you'll see recommending a 10 uF inductor and the graph shows it's possible to have up to around 100mA on the leds with ~3v input, and 50mA should be doable with as low as 2.5v

author: Mecanix
author_rank: Frequent Contributor
timestamp: August 08, 2022, 07:27:17 pm
content: Hard to argue here. Without wasting time I've put up both the PAM2841 & MCP1664 and a hand full of white leds on order. Will breadboard this on 3V3 as soon as it reach me.If it all works out I'll call it a day and add that in the FFC breakout board I'm preparing for the display.My sincere appreciation and thanks, Sir.I'll report back in a few day.