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TLC5940: On the cascaded chain of TLC5940, it happens that ein IC does receive signal but does not transfer it out.

Rompel Schichtlem
Prodigy 220 points
Part Number: TLC5940

Hi,

I have developped my board based on TLC5940 as you can in the joined picture.

I have cascaded 15 of this IC. having finishe the development I order the board and start doing some Test. It happen out of the 10 board that I order only 4 are working as expected.

Making test on defect board, it happens that the sixth driver received signal at the input, but does not transfer it at its output. it means the transfer signal between sheet Tr1 and tr2 are not occuring.

What could be the issue?

  • 0
    TI__Genius 12915 points

    Hi Rompel,

    First of all I think we should make sure the 6th driver work at proper condition. Could you help to measure the voltage of VCC and IREF, and also capture the plot of SCLK / SIN / XLAT / BLANK?

  • 0 in reply to Hardy Wu
    Prodigy 220 points

    hello Hardy,

    thnaks for your prompt feedback. I measure the voltage on Vcc which is 3,8V and the voltage on IREF ist 1,24V. on first picture blank is rosa and xlat is blue.

    on the second picture blank is rosa, yellow is Viref and  sclk is blue and SIN is the remain.

    Like I said, the sout pin remain low.

  • 0 in reply to Rompel Schichtlem
    TI__Genius 12915 points

    Hi Rompel,

    It seems the device works properly, since VIREF is 1.24 that internal LDO is working. And input signal also seems OK. You could read SIN to check if it is correct as your setting. I did not meet such situation that SOUT is always low if all input is OK.
    Is your board OK to bypass this one and connect SOUT of 5th IC to 7th IC? 

  • 0 in reply to Hardy Wu
    Prodigy 220 points

    Hello,

    thanks for the feedaback. Having lokk at it in microscope, I saw that the IC was not centered by soldering and the pin was not connected. I have remove the IC and soldere it back and it is working well.