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TLC59108F: LEDs won't light up

Matteo Bonino
Prodigy 100 points

Part Number: TLC59108F

Dear all, good morning and happy new year ! 

I'm currently in the prototype production, for a home entertainment unit, which will have STM32U5 based user interface (display, encoder, etc..)

Among the different features, I'm deploying LED rings (RGB, common anode) , to be controlled by a pair of TLC59108F. You can see the draft schematics attached here. 

I'm struggling to have the LEDs light up. I'd ask you if you see anything wrong, please.

Some further information:

  • The two TLC59108F share the same I2C3 bus. SDA and SCL pulled up by means of 4.7K resistor
  • TLC59108F's Reset pins, connected to STM32 GPIO (pulled up internally within the STM32)
  • TLC59108F 'a': all A0-A3 to ground (address '40h', shifted left to include W=0, so 80h)
  • TLC59108F 'b': all A1-A3 to ground, A0 to 3.13V (address '41h', to be shifted left, so 82h)
  • Outputs 6, 9, 11 go to cathode of RGB LED ring. (common anode powered by 5V)
  • On the firmware side, first thing I do is to invoke the Mode1 register, switching the oscillator on (00h register, 00h value). Then I wait some 200mS.
  • Then I invoke the LedOut register, activating the LEDs
  • Finally, I adjust the individual PWM brightness control registers

However, I still cannot have the LEDs light up.

Anything wrong, as you can see from my notes ?

Thanks so much in advance to all !

Matteo

TLC59108F.jpg

  • 0
    TI__Mastermind 34925 points

    Hi, Matteo

    Our expert will reply you tomorrow.

  • 0
    TI__Genius 9180 points

    Hi Matteo,

    1. Do you see successful I2C communication with ACK signal?

    2. What is the VLED voltage you applied on each string of the LED? What is the forward voltage of each LED? This is to check if there will enough voltage for the LED to light up.

    Regards,

    Emma Wu 

  • 0 in reply to Hongjia-Wu
    Prodigy 100 points

    Dear Wu, thank you very much for your feedback.

    I've resolved at the end. The reason why LEDs did not show up was the way the LEDs are wired, in my unit. I thought the three pins of my unit (those connected to pins 6,9,12 of TLC59108F) were the LEDs cathode, as seemed to appear from the documentation.

    On the contrary, one email to the led / encoder unit vendor clarified that those pins are actually control pins which shall be at logic level '1' to light the LEDs. Those pins drive the gates of three mosfets in fact, which sink the LEDs to ground with logic level 1. 

    Hence, I've removed the mosfets, and I put the LEDs cathode in direct connection with the pins 6, 9, 12 of TLC59108F (as I've developed the interface already). Since then, all is working smoothly.

    Thank you very much for your support, and sorry if the issue was on something else 

    Cheers, a good day

    Matteo

  • 0 in reply to Matteo Bonino
    TI__Genius 9180 points

    Hi Matteo,

    Glad to hear that the issue has been resolved and thank you for letting me know. I will close the thread then. 

    Regards,

    Emma Wu