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LM5118: Quick look at my layout and BOM before fabing board?

Brad Mitchell2
Prodigy 80 points
Part Number: LM5118

I have put together a design based on the webench power designer that allows for 9v to 60V input 50V output up to 0.5A.

I'm not an expert at laying out the circuit and between the person that laid out the board with this part on and myself reviewing we feel we could use another set of eyes to make sure there are no real glaring errors. 

As well just a quick glance at the BOM would be appreciated. Could I upload these 2 files for any feedback from TI? 

(CK plot and BOM)

Regards, 

Brad Mitchell

  • 0
    TI__Guru 65170 points

    Hello Brad,

    Sure, you can upload these files for a review. pdf versions of each layer are normally sufficient.

    Another possibility for the layout is trying to keep it very close to the EVM because this is a tested and well working layout.

  • 0 in reply to Brigitte
    Prodigy 80 points

    HI Brigitte, thank you. they PCB designer did follow the EVM as much as possible , but it's always a good thing to have another set of eyes to look at it. 

    55783A-55783.pdfCARRIER-HP-REVA-PRT.xlsx

  • 0 in reply to Brad Mitchell2
    Prodigy 80 points

    Hmm looks like it only uploaded the parts.. Here's the ck plots

    3225.55783A-55783.pdf

  • 0 in reply to Brad Mitchell2
    TI__Guru 65170 points

    Hello Brad,

    Please share your schematic as well. I need this as a reference. To me it seems that the diodes you are using are to small to dissipate the power.

    The layout is not very close to the EVM layout. Please change at minimum the following:

    - The IC needs to be connected to AGND. Make sure that no power path is passing the IC and connect it via another layer to PGND.

    - Remove the PGND ring you have around the AGND.

  • 0 in reply to Brigitte
    Prodigy 80 points

    Hi Brigitte,

    Here is the schematic. I'm surprised about the comment about the diodes not being large enough since they cam right out of the webbench power designer export.. but let me know what you think. 

    Regards, 

    Brad Mitchell5118_schematic.pdf

  • 0 in reply to Brad Mitchell2
    TI__Guru 65170 points

    Hello Brad,

    Thank you for the schematic. The schematic result I am getting from Webench with the above voltage and current levels is different to your design.

    Please check especially the used components again with your setting of Webench.

  • 0 in reply to Brigitte
    Prodigy 80 points

    Brigitte,

    Hmmm that's interesting and scary.  

    This is the design that I had exported and am trying to replicate. I believe that this is very similar to what I have in my schematic. 

    https://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=36A31D46E0A5A793

    Am I doing something incorrectly with webbench that you get different results? 

    I chose for some of the passives alternates to get 0805 packages. Is that the main difference?

    Regards, 

    Brad

    Just now I ran the simulator again with the same input parameters and get different values for the inductor, etc. what is going on here? 

    https://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=70AC069FC6D9E59C

    https://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=70AC069FC6D9E59C

  • 0 in reply to Brad Mitchell2
    TI__Guru 65170 points

    Hello Brad,

    In general, it is possible that the Webench model changes somewhat over time as we update it regularly.

    A different inductor value can be used as long as the compensation components are updated accordingly. A bigger inductor is used if the ripple current shall be smaller and the transient response can be slower. So it is not scary that these values are different for different designs, e.g. you might have used a different optimization in your first design and I was interested which optimization you used.

    In general I recommend to stick as close as possible to the EVM layout. Please check the differences.

    In addition for your design I recommend not using 2 diodes in parallel as long as they are not in the same package. Better is using a single diode that is able to handle the full power.