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TLC5947 radiated noise problem

Hi All,

We are using several TLC5947s to drive (hundreds of) leds on a control panel. All works very nicely. However the panel is quite close to a high sensitivity audio input board and we find that the PWM circuit is radiating noise at about 2KHz. It is worst at about 2/3rds brightness. Moving the panels apart reduces the noise. Can anyone suggest a solution please.

Thanks

Richard

  • Hi Richard,

    Could you try adding small Cap on output to decrease the slew rate?

    Best regards,

    Feifei

  • Thanks Feifei, we may try this but with hundreds of leds, thats hundreds of caps so affects costs!

    Further investigation shows the problem comes from some radiated and some conducted noise. So the solution is going to be based around a separate led supply and ground direct to the psu from this pcb (to minimise conducted noise) and a "quiet ground" plane over the whole board to minimise radiated (inductively coupled) noise from the supply lines. Also increasing the distance between our high gain (60dB) analog circuits and the led board helps alot too. Surprisingly a sheet of steel between the boards made no difference - seems it is a bit of a "black art" this sort of noise issue!

    Best regards

    Richard

  • Hi Richard,

    As you have mentioned, PCB layout are very important for radiated issue, a whole complete ground and some cap in kep points will be help for the this issue.

    Best regards,

    Feifei