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LM3407 EMI

user3614547
Prodigy 10 points
Other Parts Discussed in Thread: LM3407

Hello,
we are using the LM3407 LED driver in a LCD(TV also with analog tuner) application. The chip and the peripheral devices are plaeced on the motherboard of our LCD. The LEDs are placed on a separate PCB which is connected with a cable the motherboard with a length of approximately 6cm.

We noticed that if we switched on the LEDs we could see a lot of noise in the TV picture. We assumed that this might be an EMI problem. Probably the cable to the LED board is working as an antenna. To suppress the emmitted noise we decided to put a ceramic capacitor between GND and the LX pin of the driver. This had a great effect to the emmited noise. We couldn't see any more noise in the picture whth active LM3407. The LEDs worked properly as normal.
Now my question is, if this modification of the circuit around the LM3407 is OK? Or might there be some problems?
Thank you very much for any support!

  • 0
    Prodigy 90 points

    You would be discharging that cap on every cycle of the inductor through the chip, so even a 1uF cap may amount to a significant amount of energy when you charge and discharge it 420,000 times a second.

    You might want to try it, but keep a finger on your chip to see how hot it gets, and values for the cap should be in the pF or nF range.

    Cheers