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TLC59581: ES-PWM, frame rate queries

Reno Adley Prawoto
Prodigy 110 points
Part Number: TLC59581
Other Parts Discussed in Thread: TLC5958

Dear TI experts,

After reading the application report for TLC59581, I have some questions that I would like to confirm about ES-PWM. 

1. Is the multiplexing ratio which is 1/32 represents the 32-row scan of the LED matrix ? If it does, then if I want to drive 96x96 px display, will it require total of 18 pcs of TLC59581 to drive it with 1/32 multiplexing ratio just like illustration below ?

32x16 32x16 32x16 32x16 32x16 32x16
32x16
32x16

2. In the 8+8 mode, and 7+9 mode, I observe that 7+9 mode will have higher visual rate, but the two of them will have about the same frame refresh rate ? Is there a method to improve the refresh rate because the one in tidu370 the refresh rate reach 60 Hz ?  My calculations are provided below :

interval between segments (deadtime) = 0.1us

frefresh = 1/tsub-period

frame rate = 1/display-period

8+8 mode :

frefresh = 1/ [(257x32)/33MHz+31x0.1us] = 3963.3 kHz

frame rate = 1/[(tsub-period x 256)+0.1us x 254] = 15.475 Hz

7+9 mode :

frefresh = 1/[(129x32)/33MHz+31x0.1us] = 7800.87 kHz

frame rate = 1/[(tsub-period x 512)+0.1us x 511] = 15.22 Hz

3. How will cascading affect the refresh rate ? In tidu370, it uses 8 pcs of TLC5958 and cascade 4 of them but the refresh rate can still achieve 60 Hz

Thank you, looking forward to hearing your reply.

Regards,

Reno

  • 0
    TI__Genius 14295 points
    Hi, Reno,

    Proper engineer has been assigned to take a look at this and will reply you soon.

    Thanks.
    Regards,
    Kenneth
  • 0
    TI__Expert 3190 points

    Hi Reno,

    1, you are right for this question.

    2, a little mistake for this calculation

    it should be :

    frefresh = 1/ [(257x32)/33MHz+32x0.1us]

    frame rate = 1/[(tsub-period x sub-period numbers in 60Hz  256)+0.1us x 254]

    3. the cascading will affect the refresh rate, only when the transferring data for display is too long to finish within a display period.

    Regards,

    Shawn.

  • 0 in reply to Shawn Ding
    Prodigy 110 points

    Hi Shawn,

    Thank you for your answer, it clears my confussion, but I still have some more to ask.

    2. For question 2, is sub-period numbers in 60Hz defined as 1 total display period where the numbers can achieve 60 Hz ? For instance, in 8+8 mode, there are 255 sub period number, but it is too much to achieve 60 Hz, so I need to reduce it to perhaps 64 or 32 ?

    3. I see, I would like to ask further about the current consumption in tidu370. It is stated to be 2.6A at full brightness, may I know how it is calculated ? I tried to calculate myself but the result is off.

    Ir,Ig,Ib = 10,5,4 mA

    Iwhite = 19mA

    16 channels per IC = 16 x 19 = 304 mA

    4 ICs cascaded  = 304 x 4 = 1216 mA

    lighting two rows at the same time = 1216 x 2 = 2432 mA

    I think since it is 1/32 multiplexing, thus the average current is 2432/32 = 76 mA

  • 0 in reply to Reno Adley Prawoto
    Prodigy 110 points
    Dear Shawn,

    I would like to ask one more thing, if I want to use 8 bit grayscale, is it possible ? So it will be 8+0 mode. Thank you.

    Regards,

    Reno
  • 0 in reply to Reno Adley Prawoto
    TI__Expert 3190 points
    Yes, you are right.
    I will recommend to use 7+9 mode with actual 7+1 (total 2 subperiods each period) to increase the refresh rate.

    Regards,
    Shawn.