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LM3435: RGB output cap singing

Eric Steimle
Expert 2290 points
Part Number: LM3435


We have two boards with the LM3435 that a small RBG BLU for our displays.  We've noticed the output capacitors 0.47uF X5R 0402, sing during operation.  I considered changing them to say a tantalum cap that wouldn't have the piezoelectric effect, but I noticed the datasheet specifically calls out ceramic caps.

Is it possible to make that change?  Also what's the maximum voltage that pin should see when I"m picking a capacitor voltage rating?

Thank you,

-Eric

  • 0
    TI__Mastermind 28655 points

    Hello Eric,

    Vout can be as high as Vin basically. If Vin is 5V then I would say the output could be about 5V worst case.  If this is the capacitor from Vout to GND then it would be Vin + Vout. The output voltages will be the Vf of the LEDs you use but there are situations, such as open circuit, where it can be higher. As for tantalum, you could use them but they need a lot of derating to avoid catastrophic failure, I would use at least a 10V tantalum for output to input, more for output to GND. I would also state that you should will need some ceramic due to the ESR of tantalum capacitors. There are certain ceramic capacitors that have lower audible output, you can search for these. Murata has a series of ceramic. Another option is through hole which can reduce the audible noise.

    Best Regards,