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Led screen PCB

Igor Kuralesin
Prodigy 10 points
Other Parts Discussed in Thread: TLC5948A
Hello 
i have a few qestions about my PCB schematic
1) all connection between each chips are reasonable or unreasonable?
2) is there any special singal channel need to be shield alone?
3) is there request all wire of channel output at the same length to leds?
4) does this TLC5948A has function to stop the balance electric on channel? you know there is some small balance electric from channel when the led screen working under high refresh rate!  that is why we saw some leds always small light on, or it will be never happen by this chips?
5) how many layer of board you recommend? 2, 4 or even more?
6) any recommend for others?
 
Thanks in Advance!
  • 0
    Prodigy 230 points

    Dear Igor,


    I'll try to answer your questions:

    1) At first it is reasonable but you are using in this schematic drivers both from TI and Macroblock (5026). The footprint it is the same but you should choose your components from the same manufacturer for an easier design.

    The drivers always need a R connected to R-ext.

    Also you need to know what scan mode are you using and what kind of controller system (LINSN I guess)

    On the other side I do not know why are you using so many inductors...

    2) The control signals normally should be isolated from other and their lenght should be similar.

    3) Trace dissipate heat and there might be a voltage drop if they are too long. Try to keep the traces as wide and as short as possible.

    4) Drivers normally are ballanced and there is not a great difference between channel or other drivers. This normally is configured in the control system

    5) This depends on the pixel pitch mainly and the room that you have in your PCB. Normally with a pixel pitch smaller than 10 or 8 mm I'll use 4 layers design. In a four layer design normally you will use the inner layers for VCC and GND. But there are many things to think and to know about this.

    6) - I do not see electrolitic decoupling capacitors

    - Connect a decoupling capacitor between GND and VCC for every IC

    - Why so many inductors?

    - Check the demultiplexor control signals...do you have it ON all the time?


    - Connect a resistor for every driver. You can use the double resistor structure but this is not recommended by manufacturers.

    I hope to have been helpful!

    Kind regards,

    Abel

  • 0 in reply to Abel Valero
    TI__Intellectual 1820 points

    Hello,

    For your question 1, I'm a little confused about the connection of SD-in. Why don't you use cascading topology for SD-in?
    For example, SD_R1 input connected to output connector (PUT_OUT) without buffer. SD_R1 buffered and connected to driver IC UR1/UR2/UR3/UG2/UG3 at same time. This means these five drivers will use same GS data, will this be a problem?
    In normal usage, one driver's SOUT will connected to another driver's SIN.

    For question 4, what's the meaning of "stop the balance electric on channel"?

    Regards
    Mike