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TLC5973: about emc test

Herbert sun
Prodigy 30 points
Part Number: TLC5973

Hi,Ti team:

we use TLC5973 to driver RGB LED,we design a FPC which length about 700mm.We total use 8 pcs TLC5973 in the FPC.all of them driver 4 series and 8 parallel LED,The driver circuit is 20mA and the VLED is set 14.4V,The schematic is show below.

When we test RE for the product,the data is beyond the standard much,and the frequency  is 12MHZ frequency doubling which is TLC5973 Internal GS oscillator frequency. We try many method but can not solve the questio.When we remove the 5973 and drive by VLED directly.The question is disappear.So we think the re question was cause by the 5973.

Have you ever seen anything like this before,Are there any improvement measures and Suggestions?

As the project is urgent, we hope to get your reply as soon as possible

The relevant test data and schematic diagram are attached below

  • 0
    TI__Genius 12915 points

    Hi Herbert,

    Could you help to try paralleling 33pF-1nF capacitor on output pins to GND. There are no much setting of IC and frequency of internal oscillator cannot be changed.

  • 0 in reply to Hardy Wu
    Prodigy 30 points

    Hi,Hardy

    Thanks for your suggestion, I will try it.I also have tried replace these resistor to bead and add a 4.7uF inductance on the VLED but the effect was not obvious.

    If add capacitor on the output pins can't solve the question. What ohter things can we do？The FPC designed single side now.Is it  need to add GND layer on the top layer ？Do you have other product introduction which the frequency can spread？

    I'm worried  that the radiation is coming directly from the chip，this will hard to reduce it.

    From previous projects, whether there is a radiation problem from TLC5973

  • 0 in reply to Herbert sun
    TI__Genius 12915 points

    Hi Herbert,

    Sorry that we do not have device support frequency spreading.

    We do not hear radiation problem of TLC5973 before from other customers. One thing to confirm that is the device work at stable state during test (did you continually send data to IC)?

  • 0 in reply to Hardy Wu
    Prodigy 30 points

    Hi hardy

    It is a pity. When we test the device work at stable state and not  send  any data to IC.

  • 0 in reply to Herbert sun
    TI__Genius 12915 points

    Hi Herbert,

    Sorry that there is no much thing could be done at IC level to improve EMC performance.