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LMR14206: LMR14206

Ealse Noordmans
Prodigy 25 points
Part Number: LMR14206
Other Parts Discussed in Thread: LMR36006

Dear all,

can anyone help me with an EMC issue I am having with this regulator?

I am following the reference design and I have added an additional filter at the input, but the conducted emission is still too high at resonant frequency of the device

Thanks for your help

  • 0
    TI__Mastermind 35210 points

    At switching frequency?

    If at switching frequency, filter is easier as componet non-idealities become less of factor. All that should be needed to get additional attenuation would to either establish lower corner frequency for 2nd order filter or have two stage filter at input. 

    Device does not have spread spectrum unfortunately...LMR36006FSC would be one example device with spread spectrum if you were to go the route of not wanting to design big filter to get required attenuation, as spread spectrum dithers fundamental, reducing switching energy in spectrum.

  • 0 in reply to Marshall_Beck
    Prodigy 25 points

    Dear Marshall,

    yes it is at switching frequency

    We see the emission on multiple boards and multiple designs. In designs of my predecessor the level was around 47dBuV, just acceptable for classification. We use the regulator in question as a standard regulator for 24V (18-36V)to 5V application.

     

    In the latest design we have used the reference design of the LMR14206 and designed with respect to snva489C and snva721a. The additional input filter is optimized where an inductance of 470uF and capacitance of 47nF//10uF (X7R) gives the best result, mainly due to optimum resonance of the inductor and esr of the capacitor around the resonance of the regulator. In addition we have minimized loops and optimized board layout as explained in AN-2155

     

    I figured out just yesterday that the output inductor L1 is very sensitive to connection with the shield of the housing of the device. In the particular case of this design this is the most unfortunate case where the inductor is only 1cm away from the metal housing.

     

    The conducted emission decreases dramatically from 60dBuV to 42dBuV at resonance frequency. SRN6045, 33uH changed into SRR4528A-330M. This is sufficient for now, but we are still not satisfied since 40dB is still high and the required pcb space is still a lot.

    Therefore your suggestion to use the LMR36006 is a very good alternative. I have foud promising conducted emission reports and a reference design which is very compact. So better size, emi and efficiency looks promising. We are currently designing this into our design. If you like I can let you know the results.

    I can also provide more details or test results if you like. There is an NDA restriction in supplying details about the product, but some parts of schematics and layout are ok to share.

    Best regards,

    Ealse

  • 0 in reply to Ealse Noordmans
    TI__Mastermind 35210 points

    Hello Ealse,

    I will give you my email through personal messenger if you would like to share info and for me to provide additional assistance..