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Spike noise reduction and Hotrod package

Hiroyasu Koike
Prodigy 140 points

I'm choosing buck converter now.

My main purpose is to reduce spike noise(200-250MHz) .

Ripple noise doesn't matter.

Magnetic field loop canceller is not necessary.

Spread spectrum is not necessary.

I think flip-chip package and small value Cin capacitor is effective for

spike noise reduction even though the capacitor is outside the package. (embedded capacitor is expected, though)

Some datasheet specify Hotrod trademark and some datasheet doesn't. What's the difference?

In case of filtering Hotrod feature, the package is VQFN-HR or VQFN-FCRLF or WQFN.

But VQFN-HR package is not Hotrod always.

  • 0
    TI__Guru 56985 points

     

    You are filtering on an EM feature for a Low Inductance Hot-Rod Package.  While all of the Hot-Rod Packages are Low Inductance, not all of them are specifically designed to help reduce EMI, so not all Hot-Rod packaged devices are tagged with the "Low Inductance Hot-Rod Package" EMI feature, so they are not all coming up when that filter argument is selected. The lack of the tag may be an oversight, or may be that the device or package was not specifically targeting reduced EMI.  Those with the Low EMI feature will have the best EMI performance.  Other Hot-Rod packaged devices will generally also have improved EMI performance over other packages, but not necessarily as good as those with the Low EMI feature.

    For reduction of EMI in the 200-250MHz range, in addition to the package selection, I can recommend careful layout of the PVIN to PGND connection with tight coupling of an 0201 or 0402 bypass capacitor in the 1.0 - 4.7nF range.  These capacitors have self-resonant frequencies in the range of the switch-node resonant frequencies and sufficient ESR to be self-damping.  The exact value capacitor that will provide the greatest noise reduction will depend on some layout parasitics, so testing of values after assembly to best match the capacitor the parasitic L-C is generally needed.

  • 0 in reply to Peter James Miller
    Prodigy 140 points

    Hi, Peter

    Thank you for replying. Your advice will help me IC selection and schematic design.

    Probably, Low EMI feature means, measuring emission by near-magnetic-field probe and the emission amplitude is low enough.
    It's not very important for me. My concern is spike noise amplitude on VIN and VOUT conductor line, then a little different.


    Anyway, I understood 
      -VQFN-HR package is necessary condition
      -low parasitic package and small value capacitor just next to IC
      -exact value will be decided by testing on parts mounted board