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TLC59108 LED controller question about reasons for PWM (97kHz and 190Hz) frequency choices.

Carl Van Wormer
Prodigy 240 points
Other Parts Discussed in Thread: TLC59108

I am looking at the TLC59108 LED controller. This chip, and many others in the LED controller family have a 97kHz frequency controlling the individual LEDs and a 190Hz frequency controlling the global dimming. I'm trying to learn more about these two special frequencies. I've found no information in the E2E support, as suggested by TI tech support. Can you direct me to some engineering resource to help me understand why these two values were chosen?

 

  • 0
    TI__Expert 3460 points

    Hi Carl,

    This is a difficult question because the frequencies came from a design decision. Unfortunately, I can't reach the original design team to get a full understanding. Are there any concerns you have about those frequencies?

    Thanks,

    Harry Kennedy

  • 0 in reply to Harry Kennedy1
    Prodigy 240 points
    I would like to understand the reasons behind the design decisions. They selected those "strange" frequencies for specific reasons. If I knew those reasons, I might not make mistakes in my surrounding design choices. For instance, if they just made the choices to stay out of the range of microphonics of the ceramic capacitors, I might want to check my design for those attributes. If they made the choice because of non-interference with lighting for an NTSC camera, I might want to watch out if I was doing a non-standard video interface. It may be that these were arbitrary choices based on the number of flip-flops in the FPGA they were using for prototyping, but there may have been some real and significant reasons these values were chosen. If you can contact the original design team, the mystery could be solved. Inquiring minds want to know.
  • 0 in reply to Carl Van Wormer
    TI__Expert 3460 points
    Hi Carl,

    Looking more into this, I would consider the following about the two frequencies.

    97KHz is well above the audio band. Another reason 97KHz is a good frequency is because the 3rd harmonic is still below the AM band.

    190 Hz is a low frequency that still allows the eye to perceive it as a continuous light, and not blinking.

    We don't see any other concerns, but feel free to send me an email at h-kennedy@ti.com if you had any other specific concerns.

    FYI: one resource I used was this: www.eetimes.com/document.asp

    Thanks,

    Harry Kennedy