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LMZ20502 and LMZ21701 EMI performance info

Other Parts Discussed in Thread: LMZ21701, LMZ20502

Both parts are listed as EMI tested in the TI product selector. However EMI test data is limited or non-existent in datasheets:

1) LMZ21701: There are 2 EMI graphs (Fig 10 and 11) at Vin = 12V, Vout = 3.3V @1A.

  • Is LMZ21701 OK for 12V-to-6V @1A in terms of Class B limits with higher input current?
  • Shown EMI performance is based on eval board layout and cap values, correct? 
  • The inductor is non-shielded, right?

2) LMZ20502: Again, the integrated inductor is non-shielded, right? Any EMI data on LMZ20502 and recommended component values and layout in the datasheet for the following cases?

  • Vin = 5V, Vout = 3.3V @2A, should be the worst case.
  • Vin = 5V, Vout = 1.8V @2A
  • Vin = 5V, Vout = 1.0V @2A

Thanks.

  • The inductor on both of these modules is a non-shielded chip inductor.

    I have attached the user guides for these devices; they include more EMI data.

    The EMI testing was done on the EVM boards with the components specified.

    Of course the EMI performance that the customer will get depends on board layout and many other considerations.

    Unfortunately, we do not have data for the 12V to 6V case.

    snvu180a-2.pdf

    snvu181.pdf

  • Thanks Frank.

    1) Input filter is mentioned in LMZ21701 user guide in the conducted EMI plot. Input filter will help with radiated EMI too, correct?

    2) What is the preferred layout since it is not clear in the eval board? Should the input LC filter be closer to the VIN (between CIN and VIN) or between external supply and CIN?

    3) Also, about the smaller caps at COUT? Why the 3X1000pF in Figure 13 instead of something like 1000pF, 0.01uF and 0.1uF?

  • I have attached a picture of the LC filter used.  It should be placed as close as possible the IC.

    The smaller caps will have smaller parasitic R and L, this will provide better filtering.

    EVM_APP_NOTE_CONDUCTED_EMI_FILTER.pdf