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TLC59284: Data between IC's not working correctly

Gerhard Coetzee
Prodigy 10 points
Part Number: TLC59284

Good day,

 

I am running 20x tlc59284's in series. The CLK and Latch pins are all connected - Total CLK track length about 1450mm. The Data pin runs from one to the next between the SDI and SDO pins.

I have added a 74HC14 after every 4th tlc59284 IC, but bypassed these when the same (explained next) problem occurred at every 74HC14.

My problem occurs between the 4th and 5th tlc59284 IC. The last "value" of the 4th will become the 1st "value" of the 5th. Meaning, an additional data bit will be added at that point, equals to the 64th bit in my array. This happens with both on and off values...

I have removed the 74HC14's due to the same occurrence at each position after a 74hc14. These chips were successfully used with 74hc595's to 'filter' the signal and keep the voltage high and clean.

I am using 5v in this system, using both Arduino and Raspberry Pi, with TTL-converter, with the same result.

I have put a delay between CLK pulses, with no success. I have considered a voltage drop during switching of the pulse pin, but all the other IC's follow after where the problem occurs and seems to not occur again.

I will add my schematic along with enlargement of a section. This just repeats throughout.

I hope someone can assist, as this random bit is causing nothing to work correctly.

I have considered a faulty chip, but can't imagine why only 1 bit would be out of place...

 

Kind regards

Gerhard

 

  • 0
    TI__Genius 12915 points

    Hi Gerhard,

    This is weird that the device adds one bit in SOUT. Firstly could you help to share how you determine it is an added bit? If the filter works to make whole system works properly, it seems more like a noise signal pulse between 4th and 5th driver but not a additional bit.

    Is there a waveform of 4th driver SIN/SCLK and 5th driver SIN/SCLK on input pins to see if the data is correct?

  • 0 in reply to Hardy Wu
    Prodigy 10 points

    Hi Hardy,

    My LED layout is in the shape of a cross and each of the sections of the cross consists of 64x LED's - 8x8, run by 4x Drivers. 

    When I first assembled the PCB and ran shapes through the LED's, the shapes came out almost right. Sometimes some bits would be out of place. I then ran a script that would light up 64x LED's at a time and then 64x OFF. I started noticing an addition as it moved further along. I then changed my code to do 63x, pause, and then add one and pause. This confirmed my theory and I can see the addition showing up the moment the 64th is pushed through. This happened with both ON and OFF. Note that this happens at random. I cannot find a pattern in which it occurs...

    I have not checked the waveform, as all IC's before and after this pair is connected to the same track. I would think that should the waveform be the problem all of the IC's would have a similar effect?

  • 0 in reply to Gerhard Coetzee
    TI__Genius 12915 points

    Hi Gerhard,

    As you mentioned, all drivers are cascaded in one series right? So between 2 sections, is the trace very long between the last driver of former section, and the first driver of the next section? And the SCLK signal comes from your controller directly? The distance difference between DATA trace and CLOCK trace may cause some transfer delay, I am not sure if the timing still meet driver's requirements. It is better that we have a waveform to show what the driver get exactly.

  • +1 in reply to Hardy Wu
    Prodigy 10 points

    Hi Hardy,

    Thanks for your assistance.

    There are 2x sections where the traces are longer than the other, that is between 4&5 and between 16&17. Between these the DATA, CLK, LATCH and even the BLANK are of very similar length. and the problem did not occur between 16&17. I have put up to a 50ms delay between clock states, which should help with the delay, but...

    I have found my problem though. I missed the fact that I put a 74HC14 before each section, so when I removed "all" of them, I missed the first one. Removed and bypassed it and everything works...

    I have put the LATCH, CLOCK and BLANK through the 74HC14 and suspect that there is some delay between those and the DATA causing my problem. I thought the BLANK pin to be more susceptible to problems because of the long trace, when I designed it, but know better now. I will test the same, but with the DATA going through the 74hc14 as well. This has worked for me in the past.

  • 0 in reply to Gerhard Coetzee
    TI__Genius 12915 points

    Hi Gerhard,

    Nice to hear that you find the cause. Please let me know if there are any further question.