• State
  • Locked Locked
  • Replies 5 replies
  • Subscribers 62 subscribers
  • Views 5976 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

RGB matrix driver schematic verification

Łukasz Czapla
Prodigy 30 points
Other Parts Discussed in Thread: TLC5947, TLC5951

Hi Everyone, 

I am trying to make a driver for 24x24 RGB matrix (it  consists nine 8x8 RGB matrixes with common anode). To driving columns I use TLC5947 (as a constant currnet sink) and for rows it's ULN2803A. I was wondering if there are any contraindications to use them - the TLC's - in series. Each can handle one 8x8 rgb matrix, but as I've mentioned I want to do something bigger. 

TLC5947:

I read that current which is set by Riref resistor is the same for each output. Is there possibility to set it different for each of the outputs? 

How big capacitor I should put between VCC and GND in TLC? Are there any rules for this? Power which I supply or something else?

ULN2803A:

There is a COM pin (on my schematic it is 'WD') which connect cathodes of all clamping diodes in this element. My question is: This pin should be connected to ground or something else or it could be floating?

Overall:

I want to be able to manage dots individually from matrix. 

I want to know if I need one uC or more? 

I would be appreciate if you could give me some clues or suggestions with this project. Please don't be mad at me for my language and knowledge. This driver is my first project. 

Thank You,

  • 0
    TI__Intellectual 955 points

     Hello Lkasz,

    TLC5947:

    I read that current which is set by Riref resistor is the same for each output. Is there possibility to set it different for each of the outputs? 

    >>> There is no way to set different output current between channels. Please control LED brightness by gray scale data in TLC5947.

    How big capacitor I should put between VCC and GND in TLC? Are there any rules for this? Power which I supply or something else?

    >>> No any rule. But 0.1uF ceramic capacitor would be general part.

     As you know, TLC5947 has internal oscillator for PWM control and the PWM timing (output current on/off timing) can't be controlled by extenal reference colock.

     In case of Multiplex control  display panel, accurate PWM timing control with extenal clock would be needed.

     So I  recommend you to use TLC5951 , 24 channel PWM LED. TLC5947 is used for static LED display in general.

     Best regards,

     Kazuya Nakai.

     

     

  • 0 in reply to Kazuya Nakai
    Prodigy 30 points

    Dear Kazuya,

    Thank You for response to my questions. 

    Why accurate PWM timing is needed? What kind of problems I would have if I use internal clock from TLC5947?

    Is it very important if I want to display simple pictures (not animations)?

    What do you mean "static LED diaplay?" 

    Best regards, 

    Lukasz

  • 0 in reply to Łukasz Czapla
    TI__Intellectual 955 points

     Dear Lukasz,

     TLC5947 internal oscillator frequency is not completely same  between devices. The frequency range is 2.4~5.6MHz.  If you use 1 display period (4096 internal clock time length) for 1 line display of your multiplexing display, the 1 display period is not same between devices. If you don't need accurate brightness control, it may be no problem.

     Staic LED display means no multiplexing display and 1 constant current output is connected to only 1 LED lamp in the statice LED display case. In case of multiplexing LED display, 1 constant current output is connected to two or more LED lamp.

     Best regards,

     Kazuya Nakai.

     

  • 0 in reply to Kazuya Nakai
    Prodigy 30 points

    Dear Kazuya,

    I understand static led display, but I'm not sure if I think properly with the internal clock problem.

    In one device there might be e.x. frequency 3 MHz, and in another there wiil be 4 MHz. ( 1/3 us and 0.25 us). 

    Outputs are turned on after 5th rising edge of internal oscillator clock. So it means that between two devices the outputs will turn on and sink current in different time period. And it may cause blinking? Am I right?

    Best regards,

    Lukasz Czapla

  • 0 in reply to Łukasz Czapla
    TI__Intellectual 955 points

    Dear Lukasz,

    I think the different brightness issue between two devices would be happen.

    Output on time for 2048 grayscale data (half of full gryscale) is about 512us when the internal oscillator frequency is 4MHz. If 1024us is total display time of 1 common line in multiplexing drive method, then the on duty ratio is about 50% (512/1024). When the internal oscillator frequency is 3MHz, total output on time for 2048 grayscale data in 1024us is about 676us. The on duty ration is 66% (676/1024). So LED brightness in case of 3MHz oscillator frequency is brighter than 4MHzcase.

    Best regards,

    Kazuya Nakai.