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The number of the bits of PWM(TLC5958)

Other Parts Discussed in Thread: TLC5958, TIDA-00161

I'm Tokumoto, Marubun from Japan.

I would like to know about TLC5958.

According to the page4(system specification summary) of TIDA-00161(tidu370.pdf),
specification of the gray scale is described as "~14bit".

Can TLC5958 change the number of the bits of PWM into 14bit  from 16bit?
 (I was not able to find the change method from a data sheet and
    an application note(slva645) of TLC5958.)

Best regards.

  • Tokumoto-san,

    For your quesiton, Yes, tlc5958 can be worked in 14bit grayscale.

    You can find application note in below link:

    http://www.ti.com/product/TLC5958/technicaldocuments

    In the application note, tlc5958 is described working in 8+8 mode. Actually tlc5958 can also be working in 8+6 mode.

    tlc5958 can support 8+6 mode, that means you can send 64 sub-period then follow up with a Vsync command, it will enter next frame rate display.

    You don’t need to finish all the 256 sub period. Timing is below. Be noticed that, you still need sending 16bit GS data while working in 14bit mode.

      

    Best regards,

    Feifei

  • Feifei-san

    Thank you very much for your reply.
    Please let me ask you two questions.

    (1)About 8+6 mode
           I understand TLC5958 can be worked in 8+6 mode(14bit grayscale) with using Vsync command.

          So,I intend to set the following value to GS data to adjust brightness ratio in 8+6 mode.

          For example;
            ①If GS=0,then the brightness ratio will be 0/16383 = 0%.
            ②If GS=125,then the brightness ratio will be 125/16383 = 0.763%.
            ③If GS=16382,then the brightness ratio will be 16382/16383 = 99.994%.

          Is my understanding correct?

    (2)About system specification summary of TIDA-00161
          I calculated the value of "visual refresh rate" and "Grayscale"
           described in the page4(system specification summary) of TIDA-00161(tidu370.pdf).

          The results of calculation are as follows. (in 8+6 mode)

         tsub-period = (1/33MHz)×257×32+31×tded=0.280(ms)
      
          *tded:dead time=1us

        Visual Refresh rate = 1/tsub-period = 3.57(kHz)

        Total Display Period = tsub-period×64+63×tded = 17.997(ms)
      
         Frame rate = 1/Total Display Period = 55.566(Hz)

          From the above results,I think TLC5958 cannot realize "frame rate = 60Hz"
          even if  the number of the bits of PWM is 14bit.

         Is my calculation incorrect?

    Best regards

  • Hi Tokumoto-san,

    For your 1st question, if tlc5958 works in 8+6 mode.

    You need to set below for GS data.

    Still send 16bit data with 2 LSB 2b'00 and high 14bit represent the real GS data.

    For example: GS=4h0004, then the brightness ratio will be 1/16383.

                             GS=4h0008, then the brightness ratio will be 2/16383.

                             GS=4hFFFC, then the brightness ratio will be 16383/16383.

    For your 2nd quesiton, the calculation is correct.

    If you want to realise 14bit GS in 33M and 1/32 multiplexing and 60Hz, you can reduce dead time.

    Or you may want to realise 13.8bit GS.

     

    Best regards,

    Feifei

  • Hi,Feifei-san.

    Thank you very much for your prompt reply and the detailed explanation.

    I understand your answer.

    Please let me ask a little bit in regards to that.


    (1)About 8+6 mode
      ①When I use TLC5958 in 8+6 mode,I intend to set "0" to SEL_PWM(FC2:bit14).
        Is my understanding correct?

        ②Is there special setting(FC1,FC2 register) compared with 8+8 mode?


    (2)About 9+5 mode
       ①Can the TLC5958 be worked in 9+5 mode(14bit grayscale) with using Vsync command?

       ②If the above working is possible,then I intend to set "1" to SEL_PWM(FC2:bit14).
       Is my understanding correct?

     ③Is there special setting(FC1,FC2 register) compared with 9+7 mode?


    (3)About other PWM mode
      ①Can the TLC5958 realize 13bit or 15bit or other bits by changing a timing to send Vsync command?

       For example;(8+5mode)
         GS=4h0008, then the brightness ratio will be 1/8191.
                 GS=4h0010, then the brightness ratio will be 2/8191.
                 GS=4hFFF8, then the brightness ratio will be 8191/8191.

    Best regards

  • Hi Tokumoto-san

    Your understanding is correct.

    For your question:

    1)About 8+6 mode
      ①When I use TLC5958 in 8+6 mode,I intend to set "0" to SEL_PWM(FC2:bit14).
        Is my understanding correct?

    Yes

        ②Is there special setting(FC1,FC2 register) compared with 8+8 mode?

    No special setting


    (2)About 9+5 mode
       ①Can the TLC5958 be worked in 9+5 mode(14bit grayscale) with using Vsync command?

    Yes

       ②If the above working is possible,then I intend to set "1" to SEL_PWM(FC2:bit14).
       Is my understanding correct?

    Yes

     ③Is there special setting(FC1,FC2 register) compared with 9+7 mode?

    Nothing special


    (3)About other PWM mode
      ①Can the TLC5958 realize 13bit or 15bit or other bits by changing a timing to send Vsync command?

    Yes, it works.

     

    Best regards,

    Feifei

  • Hi,Feifei-san.

    Thank you very much for your prompt reply.

    I am able to reply to my customer immediately by your support.

    Please let me ask you a question.


    I understand that I do not have any problem even if I insert an interval(SCLK stop)
    on the way writing in data(FC1,FC2,GS Memory) as follows.

    For example(48bit GS Data Write command)

    プレゼンテーション1.pdf

    Is my understanding correct?

    Best regards

  • Yes, there will be no problem if you insert interval during data writing, as long as there are no latch signal.

    Best regards,

    Feifei