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LP8556: LP8556 PWM Dimming Frequency Range

Kevin Wen
Intellectual 2235 points
Part Number: LP8556

Hi team,

My customer BOE is evaluating LP8556 on their high resolution panel for VR applicaiton, they want to set the LED driver PWM dimming frequency to as low as 60Hz (FSET pin shorted to GND, PWM dimming frequency is the same as input frequency)

would you please suggest if LP8556 could support PWM frequency between 60~75Hz? thanks. 

Kevin

  • 0
    TI__Expert 4565 points

    Hi Kevin,

    Using PWM in freq = PWM out freq mode will disable phase shift of PWM dimming output causing PWM only mode operation.

    In this case, it may help resolution wise, but LED flickering may be visible due to too low PWM frequency.

    And min freq of PWM input is 75Hz according to datasheet, so 60~75Hz operation is not guaranteed. Actually, I've checked this freq range on EVM and it worked well, but I don't recommend this condition for the reason I stated before.

    Increasing PWM output resolution can be obtained by using dithering function.

    Input can be still 75Hz~25000Hz. Lower freq will be better to have higher input resolution. PWM out freq can be min(2402Hz).

    If PWM in freq = 75Hz, input resolution will be log2(10000000/75) = 17 bit, but max PWM input data can be 16 bit

    PWM out freq = 2402, output resolution can be log2(10000000/2402) = 12 bit, dithering can enable additional 3 bit resolution, so final resolution can be 15 bit which still supports PWM phase shift. If hybrid or current dimming is used, dithering can't be applied on current dimming range and max resolution can be 12 bit.

    Hope this helps,