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Original question:

LMR33610: LMR33610/LMR33640 EMI

LMR33620: LMR33620 PACKAGE EMI?

kwon
Intellectual 850 points
Part Number: LMR33620

Hi.

There are three questions.

1. There are two types of LMR33620 PACKAGE: DDA and RNX. Is DATASHEET 1PAGE Low EMI only valid for RNX PACKAGE?(RNX=LOW EMI, DDA ≠ LOW EMI???)

2. Does the LMR33620 RNX PACKAGE have the same EMI characteristics as the LMR33620-Q1?

3.It is described as LOW EMI of LMR33620-Q1. The DATASHEET 30PAGE EMI DATA is Fsw=400 KHz. Do 1.4MHZ and 2.1MHz have different EMI characteristics? Is it not LOW EMI?

Best Regards,

KWON.
  • +1
    TI__Guru* 75570 points

    Hi Kwon,

    Thank you for posting.  You are correct that the RNX package would have better EMI performance because of being leadless. 

    Sorry I do not have the data to answer your second question, but note that EMI is largely depending on external circuit layout, and the emission differences due to these two package differences should be minimal. 

    Regarding your third question, at higher frequency you would see lower frequency emission peaks drifted to higher frequencies, and these peaks may be smaller because the same filtering would have better attenuation at higher frequency.  For high frequency range, the performance should look similar.  

    Note that increasing the freq from 400kHz to 1.4MHz may not be a good idea in some applications if you want to avoid the fundamental frequency emission in the AM band.  1.4MHz enters the AM band even the peak may become smaller than switched at 400kHz.

    Hope this clarifies.

    Best Regards,

    Youhao

  • +1 in reply to Youhao Xi
    Intellectual 850 points

    Thank you for the explanation.

    I would like to receive an accurate answer to question 1.

    dda package is not low emi as described in data sheet 1 page?

    lmr33610dda/20dda/30dda/40dda is not low emi?

    Best Regards,

    KWON.
  • +1 in reply to kwon
    TI__Mastermind 19891 points

    Hello Kwon, 

    The EMI performance depends a lot on the PCB layout and external components. You can have worse EMI even with the best package + bad layout. 

    The LMR33620 devices come in two packages, DDA and RNX. The DDA package has leads, which some customers prefer for easy soldering and joint inspection. The RNX package has lower parasitics and provides symmetrical VIN path, both of which help with EMI. 

    But, the DDA package pinout is also carefully chosen to enable you to have a good PCB design for low EMI. For example, VIN and PGND are right next to each other allowing the direct capacitor placement. Also Boot and SW are next to each other. 

    With that said, considering the best possible layout for both packages, the RNX package is expected to perform better in terms of EMI because of the HotRod package (no bond wire) and parallel input current paths due to the symmetric VIN and GND pinout. 

    Regards, 
    Denislav

  • +1 in reply to Denislav Petkov
    Intellectual 850 points

    Thank you.

    Best regards,

    KWON.