TLC5947 - what capacitor for the reserved space on the board

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schoschie
 
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TLC5947 - what capacitor for the reserved space on the board

Post by schoschie »

Hi, the TLC5947 driver board has space reserved for an optional capacitor, but I found no details on this. The TLC5947 datasheet has a decoupling cap in the example schematics on the first page, but does not note any rating or other details about it.

I can only guess that it should be some kind of buffer or decoupling cap, but since it's not soldered in by default, it doesn't seem necessary in most cases. The question: Under what circumstances would it be advisable to solder in a cap? What cap should I use? Thanks for enlightening me :)

Agent_24
 
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Re: TLC5947 - what capacitor for the reserved space on the b

Post by Agent_24 »

Are you talking about this one? https://www.adafruit.com/products/1429 It already seems to have the decoupling capacitor as mentioned in the datasheet - one of the SMD ceramic ones, 0.1uF is the usual value.

If the capacitor space you are talking about is the one called "Opt. V+ Cap" I expect you only need that when you are using the "optional V+" supply and If the power supply used is far away via a long cable. You would probably want an electrolytic capacitor at least 100uF there.

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adafruit_support_bill
 
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Re: TLC5947 - what capacitor for the reserved space on the b

Post by adafruit_support_bill »

Agent_24 is correct. This is for the V+ supply. A capacitor installed there will help smooth over instantaneous current peaks from switching leds. If you are seeing dimming, flickering or other interactions between LEDs, you can add a cap there. Use an electrolytic rated for at least as much voltage as your V+ supply. And mind the polarity when installing.

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Aqualize
 
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Re: TLC5947 - what capacitor for the reserved space on the b

Post by Aqualize »

Bringing up an old thread but the subject is the same.

I've bought 3 TLC5947 Adafruit LED PWM breakout boards, will be connected daisy-chained. I don't know if I need it but it would be much easier to add the capacitors before I get started mounting the boards in the project. I looked through the scrap and found a used desktop switch where I found 3 electrolytic capacitors. Marked as 16 V and 470 μF.
I know very little about this (capacitors) so the question is: 470, is that okay? Or should I try to get closer to 100 μF. Agent_24 wrote "at least" 100 so I hope these will fit the bill.

Thanks for any help
Last edited by Aqualize on Wed Dec 10, 2014 5:54 pm, edited 1 time in total.

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adafruit_support_bill
 
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Re: TLC5947 - what capacitor for the reserved space on the b

Post by adafruit_support_bill »

Marked as 16 V and 470 μF.
Those should work fine.

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