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Vsync in backlight driver?

Tung Shen Chew
Prodigy 10 points
Other Parts Discussed in Thread: LP8545

Hi all,

I am building a simple circuit to control an embedded-DisplayPort LCD screen (60Hz, LP097QX1-SPA1), using the LP8545 to power the backlight. May I ask if the Vsync signal on the LP8545 must be connected to achieve good performance? How will my screen performance suffer if I leave out this signal, and is there a way to obtain this signal from the raw Displayport interface?

Thanks,

Tshen

  • 0
    Intellectual 490 points

    My understanding is that the Vsync input is used to synchronise the backlight PWM with the video frame rate (Vsync or Hsync) to reduce the potential for aliasing or other artefacts.. Since DisplayPort does not necessarily operate synchronously with the display frame rates I don't think there is a simple way to extract a suitable signal to mimic the function of Vsync or Hsync in this case.

  • 0 in reply to Gareth Richards
    TI__Intellectual 2510 points

    Hi Tshen,

    This is info what I got:

    Main purpose for using Vsync – to reduce a “waterfall” effect. If frequency output PWM frequency is big enough, phase shift mode is  used – effect will be not visible for normal brightness level. Maybe only for very low brightness.

    For simplified control using Vsync is not necessary. And one note – better to use Hsync (freq range for LP8545 is 58..55000kHz) – “breathing” PLL can create artifacts which you are not expected to see.

    Regards,

    Sami