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    Need help to design led drivers (ZXLD1370)

    Hi,

    I'm working on the LED Dimming for automotive.

    Driver IC : ZXLD1370
    Input : 12V
    LED cuttent : 100mA (24V)
    Boost Mode
    PWM frequency (15 Pin) : 1KHz

    This noise is generated in the ZXLD1370.

    To reduce the noise? Solve other?

    Click image for larger version. 

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    ZXLD1370 datasheet
    http://diodes.com/datasheets/ZXLD1370.pdf

    •   Alt29th January 2015, 01:28

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  2. #2
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    Re: Need help to design led drivers (ZXLD1370)

    not sure what noise you are referring to............



    •   Alt29th January 2015, 03:15

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    Re: Need help to design led drivers (ZXLD1370)

    Quote Originally Posted by kam1787 View Post
    not sure what noise you are referring to............
    noisd -> high frequency sounds



    •   Alt29th January 2015, 03:23

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    Re: Need help to design led drivers (ZXLD1370)

    Quote Originally Posted by shock225 View Post
    noise -> high frequency sounds
    likely the 1KHz or harmonics thereof from the PWM

    use a LC or PI filter on the output



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    Re: Need help to design led drivers (ZXLD1370)

    IS YOUR INDUCTOR CURRENT smooth?
    Have a look at the voltage across the sense resistance...is it a regular triangle wave?
    If not then maybe you have instability.
    Sometimes, surface mount inductors cam make noise esp if the inductor current is not smooth.....also maybe the 1khz pwm may be making the inductor coils vibrate and make noise...maybe you need to go thru hole inductor to solve it....ceramic caps can also make noise, but my money os on the inductor....desolder it and solder in twisted pair wire to its pade, and solder a inductor to the end of this twisted pair and see if you still get the noise.

    Maybe it is your layout though...maybe you have routed the noisy switching node over the controller...? maybe you need to correct this, or increase the fet series gate resistance to delay the drain voltage transition.

    also GI, ADJ TADJ and REF pins....are you sure they shouldn't have a decoupling capacitor connected to them? to ground.

    My money is on the layout, or the inductor



    •   Alt29th January 2015, 23:43

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    Re: Need help to design led drivers (ZXLD1370)

    Quote Originally Posted by shock225 View Post
    noise -> high frequency sounds
    Details? Voltage ripple or Acoustic noise
    How much?
    A good design question lists your overall requirements™ The best question deserves a better answer. ™
    ... Tony Stewart EE since 1975



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    Re: Need help to design led drivers (ZXLD1370)

    Hi,

    Did you manage to solve the problem? I am having the same problem... Anyone ideas?

    Kind Regards



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