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Inductor recommendations for smallest footprint

TI Lady
Genius 4025 points
Other Parts Discussed in Thread: LM20134

I will be using LM20134 to provide few voltages in my design (couple of core voltages and IO for several FPGAs), and wanted to run inductor choice by you to see if there are any issues.

The datasheet recommends using Coilcraft MSS series inductors (shielded, ferrite core). I was wondering if the XFL4012 series (shielded, composite core) would be ok? Likely XFL4012-601ME, 0.6uH, max DCR 19.14mΩ (http://www.coilcraft.com/xfl4012.cfm). Program is very much size constrained, which is why I’m looking at a smaller footprint.
 
My Vin is 3.3V, the outputs are 1.0V, 1.2V and 1.8V. Temp range up to 85°C
For current
1.0V  at room temperature will be about 1.2A, at 85°C about 3.4A
1.2V at room temperature will be about 0.5A, at 85°C about 1A
1.8V at room temperature will be about 1A, at 85°C about 2A
 
I don’t intend to use the same inductor for all three, unless it happens to work.

thanks so much !

  • 0
    TI__Guru 71516 points

    Hi Amy,

     I ran the 1V, 3.4A, 85C design on webench for smallest footprint (attached, and design sent to you in an email from Webench).  The XAL5030 series came up as the preferred, and if you click on the "Select Alternate Part" there are dozens of other choices shown, along with the relative footprint size.   In fact, if you click on the Manuf column, it sorts by vendor, Coilcraft has 60+ coils listed, however, none are the XFL-series.  I suspect the inductance for this series is too low, as the 2.2uH is selected, this XFL he referenced is only 0.6uH - not nearly enough L. 

    I see XAL5, XAL6, XAL7-series have the smallest footprints; these are all smaller than the MSS-series, so I think these may be alternatives to the XFL-series he mentioned.  Let me know if these are acceptable for his requirements.

    -Leonard

     

     

    LM20134_1V_3.4A_85C.pdf
  • 0 in reply to LeonardEllis
    Genius 4025 points

    thanks leonard!! i feel like you're my own personal apps engineer these days!! thanks so much!

  • 0 in reply to TI Lady
    Prodigy 5 points

    For Vin of 3.3V, the outputs are 1.0V, 1.2V and 1.8V. Temp range up to 85°C
    For current
    1.0V at room temperature will be about 1.2A, at 85°C about 3.4A
    1.2V at room temperature will be about 0.5A, at 85°C about 1A
    1.8V at room temperature will be about 1A, at 85°C about 2A

    You can design for the 1V at 3.4Amp and just change the feedback divider for the other voltages.
    The inductor and output caps should be fine for the lower current higher voltages.

    See the datasheet page 16 LM20134, Table 2.
    Shows compensation changes for various output voltages using a common L and Cout.