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Thread: LED Drivers IC: Sink current using PCA9685?

  1. #1
    Unenlightened
    Join Date
    Apr 2021
    Posts
    2

    Help LED Drivers IC: Sink current using PCA9685?

    Hi, all
    I'm using a PCA9685 with a pinout board like Adafruit's. I'm trying to run a bunch of LEDs at 20 mA, and the chip is supposed to be able to source 10 mA and sink 25 mA. I understand that to have it Source, connect the LED between the PWM and GND pins and sink it between V+ and PWM.
    I've tried both ways and using a multimeter and a red LED I get 12.5 mA. Why is it not 25 in Sink? Also, why do I get 12.5 on Source mode as well?

    Is there any idea of it? so if possible a simple explanation would be nice, thanks in advance.

    Enclose PCA9685 data source as Reference: https://www.apogeeweb.net/productdet...W-118-t5Bl0pmz

  2. #2
    Flashaholic
    Join Date
    Nov 2009
    Location
    Ottawa Ont. Canada
    Posts
    443

    Default Re: LED Drivers IC: Sink current using PCA9685?

    What value of series resistors are you using? If you're not, they need to be there. Driver outputs can sink up to 25mA but they are not constant-current outputs as with some chips. See page 29 of the datasheet.

    Also, what is supply voltage to the chip and LEDs?

    Dave

  3. #3
    Flashaholic
    Join Date
    Nov 2009
    Location
    Ottawa Ont. Canada
    Posts
    443

    Default Re: LED Drivers IC: Sink current using PCA9685?

    With 5v supply and a red LED, series resistor would be approximately:

    (5.0 - 1.8 - 0.5)/0.020 = 135 ohms. Anything close should work.


    Dave

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