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TLC6983: How to solve first scan line dim and gradient dim lines

jh lee
Prodigy 70 points
Part Number: TLC6983

I'm using TLC6983 for 1mm pitch LED panel.

And only use 11-bit PWM for display because I need a very fase frame rate. (about 2000Hz).

I can't remove the first scan line dim & gradient dim with changing register FC4 [35:38].

Could you have any suggestions?

  • 0
    TI__Expert 8545 points

    Hi JH,

    it seems you already have a board designed by your side?

    the performance is related with hardware design and according to your hardware design, I can suggest to adjust the registers setting.

    so could you please provide the current information about your design?

    1. CLK rate
    2. Frame Rate(Vsync CMD frequency)
    3. Hardware design(VCC/VLED/Current/Line Number...)
    4. registers setting
    5. RGB or monochrome?
    6. ...

    if you don't want to public your project information, please contact me by email.

    my email address: monet-xu@ti.com

    BR

    Monet Xu

  • 0 in reply to Monet Xu
    Prodigy 70 points

    Thank you for your reply.

    My design is below.

    1. SCLK 12.5Mhz, GCLK 50Mhz, TSW 90GCLK

    2. 1500Hz. 

    3. VCC/VLED_R,G,B 3.4V, 

        Current : Rset 28.7kohm

        Line number : 8 line

    4. FC0 : 0x4000, 0x30070100

       FC1 :  0x0E60, 0x0094A54C

       FC2 : 0x0380, 0x00000660

       FC3 : 0x000F, 0xFFFFFF00

       FC4 : 0x1F80, 0x05404008

    5. RGB

    If you need more information, feel free to ask me again. 

    thankyou

  • 0 in reply to jh lee
    TI__Expert 8545 points

    Hi JH,

    One thing makes me confused. why you need such high frame rate?

    actually for our eye we can't catch the flicker when the frame rate is large than 120hz. And considering the camera shooting, to avoid the black line we increase the refresh rate.

    1. so could please check which parameter is 2000hz, frame rate or refresh rate?
    2. for TLC6983, the minimum PWM resolution is 12bit
    3. we suggest to separate the VLED_R with VLEDG/B because that will influence the display performance like first line dim.
    4. could you take a picture about your LED panel about the issue?

    BR

    Monet Xu

  • 0 in reply to Monet Xu
    Prodigy 70 points

    I understand your point but I need indeed 1500Hz for our application.

    1. It is frame rate not refresh rate. Vsync time is 1500Hz.

    2. I think Nsub-period minimum 16 and Gclk minimum 128 so minimum resolution is 11bit right I think.

    3. I was intended seperate VR and VG/VB but I had mistake  that VLEDB , VLEDR/VLEDG has same net. 

        blue LED and green LED minimum voltage 3.1V so I had no choice voltage 3.4V both.

    4. It's not possible for our company security policy. 

       I can watch Dark Line on each of the 8 lines on my board when I display white frame.

         

  • 0 in reply to Monet Xu
    Prodigy 70 points

    Is there any solution to my situation?

  • 0 in reply to jh lee
    TI__Expert 8545 points

    Hi Jh,

    firstly, one frame is 1/1500 = 0.67ms. but the display time is just ~0.5ms. please increase the segment length to 165 to reduce the black time.

    adjust the FC4 38-35 FIRST_LINE DIM setting. increase it step by step and check whether the issue improved.

    if it is still here, please display the whole Panel to R or G or B, and check in which condition will observe the first line dim issue.

    so what is the end application?

    BR

    Monet Xu