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LP8556: PWM dimming frequency

K.Yaita
Guru 29690 points
Part Number: LP8556

Hi Team,

I understood PWM dimming frequency can be set by PWM_FREQ [3:0] or RFSET [kΩ].
Is there any tricks to decide PWM dimming frequency [Hz]?
I believe it is better to keep out audible field..

May I have your advice?

Best Regards,
Yaita / Japan disty

  • 0
    TI__Expert 4565 points

    PWM out freq settings can be only preset values, not continuous ones.

    If audible noise by this freq is concerned, hybrid dimming or current only dimming can be considered. Current only dimming will keep PWM always 100% without any PWM switching, and hybrid mode will start PWM switching at low brightness(depending on PWM_TO_I_THRESHOLD) which is low load condition can be safer for audible noise.

    Thanks,

  • 0 in reply to Sung Ho Yoon
    Guru 29690 points

    Hi Yoon-san,

    Thank you for your support.
    I would like to ask an additional question about PWM dimming frequency.

    Is there any difference between higher PWM dimming frequency and lower PWM dimming frequency when adaptive (hybrid) dimming is used?
    I would like to know which is recommended to achieve accurate LED current at light load.

    Best Regards,
    Yaita

  • 0 in reply to K.Yaita
    TI__Expert 4565 points

    Hi Yaita-san,

    PWM dimming freq setting will change PWM freq at low brightness on hybrid dimming.

    Generally, PWM output freq is higher than a few hundred Hz, so I don't think there would be any artifacts can be detected by human eye.

    If PWM freq is too high, resolution can be lower than low PWM freq due to limited sampling clock freq.

    So, I recommend lower PWM freq as long as it doesn't have any visual artifacts.

    Hope this helps,