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LP8860-Q1 / Dimming Resolution

Kuramochi Tadahiko
Guru 28715 points
Other Parts Discussed in Thread: LP8860-Q1

Hi,

My customer requests dimming resolution such as following file.

Requested Dimming Ratio.xlsx

Can the LP8860-Q1 achive this dimming raio?

I think that it cannot achive 0.00172%/step, is it correct?

Best Regards,

Kuramochi

  • 0
    TI__Expert 4565 points

    Hi,

    The min output PWM pulse width of LP8860 is 200ns, and min freq of PWM output is 4883Hz. The period of 4883Hz is ~200us.

    200us/200ns = 1000. If you use hybrid dimming which current to PWM dimming switch point at 12.5%. Dimming ratio can be 8000.

    Step size is another concept. If PLL freq = 40MHz as a sampling freq of output PWM, and PWM freq is 4883Hz, 40MHz/4883Hz = 8191(~13 bit)

    If you use 3 bit steady dithering on top of this, 16 bit resolution(65535 steps) can be supported. 0.00172%/step = 58139 total steps.

    In order to have clean 16 bit brightness input, using brightness register will be better to test this.

    Hope this helps,

  • 0 in reply to Sung Ho Yoon
    Prodigy 150 points
    Hi Sungho,
    As datasheet show, the PWM input Dimming Ratio >13000:1 with External PWM voltages, at PWM frequency = 100Hz,
    I want to know, under this condition, Fsw=? Or it can be ignored?
    The application condition of my project is Fsw=2.2MHz, and I want to know the Min. Dimming Ratio of input PWM.
    Thank you!Best regardsSiwei LI
  • 0 in reply to siwei li
    TI__Expert 4565 points

    Hi Siwei,

    SW frequency of LP8860 is independent from PWM resolution/freq.

    Boost SW freq can be decided by SYNC(not VSYNC) input if external clock is used.

    Hope this helps,