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By seulater
#115332
I have a project where i need to make 20 led strips, each strip will have 200 RGB leds on it. I need independent control of each led.
The pcb for each string cant be much wider then the LED itself, so any part would have to go on the back side.
Anyone got an cool SPI parts in their bag of tricks that can pull something like this off ?

I am saying SPI, because I2C would just be to dam slow to update the leds.


Thanks
Jim
By seulater
#115352
That's cool, thanks. I need to see if i can find something a bit cheaper though.
I was looking at the PCA9633DP1,118, (Digi-Key: 568-3236-1-ND) PWM driver series.
User avatar
By ohararp
#115353
Jim, this is the chip you need http://www.mouser.com/ProductDetail/Tex ... cfTmq3g%3d
Same as used in this board http://macetech.com/store/index.php?mai ... 130397f969

They have been on back order forever. Seems like TI ran a huge order of them. I have thought to use these in a number of projects.
By macegr
#115361
Yeah the TLC5947 is awesome. Don't overlook the fact that the outputs can handle up to 30V...you can put clusters of LEDs in series and actually handle some decent power with this chip.

Mouser did finally get a bunch of these out there. At one point we had bought the last reel of 2000pcs and were the only ones distributing it. Sold all but a few hundred, used in the OctoBrites.
User avatar
By ohararp
#115380
garrett, when using a higher voltage say 30V are there any issues to be aware of (i.e. does the Vf of the series leds have to be within a certain threshold of VCC)? It wasn't clear to me in the datasheet if there were any constraints in terms of the Vled levels and the required voltage drop.
By gmarsh
#115388
I've used the TI TLC594x series (usually '5941) for the same application and I've been very satisfied with them.

Generally I build circuits like this with multiplexing, and since you're having 600 different LEDs on one of these boards, you'll probably want that unless having 38 TLC594x chips is acceptable in your application. Usually what I'll do is put HC595's in the same serial chain and use them to drive P-channel MOSFETs (usually a Fairchild FDC63xxP) for high side switching.
By seulater
#115389
I am going to have to start looking at some fets. I will take a look at that one you mentioned. I will also need 3 fets per led as well. the cost is going up and up ;)
By macegr
#115416
Ryan, when you use higher voltages you do want to keep the Vf of the LED series close to the power supply voltage. Otherwise, the chip has to dissipate all the extra energy, and the package can only handle 3W with good heatsinking. Typically want to keep within 1-3 volts of your supply.