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LM5117: Remote Sensing and load share with UCC29002

Oytun YILMAZ
Prodigy 40 points
Part Number: LM5117
Other Parts Discussed in Thread: UCC29002, LM5119, LM5116

Hi,

I am planning to use parallel LM5117 with load sharing. I guess a good start point will be UCC29002 which seems to provide the needed functionality. But UCC29002 requires remote sense capability on the converter side. Can I add remote sensing to LM5117 ? Above all does it make sense to use LM5117 with UCC29002  ?

  • 0
    TI__Mastermind 40040 points

    I do not think you need to have remote sensing to use the UCC29002. What specification are you trying to meet? There may be an easier solution?
    What is your basic Vin, Vout and Iout requirements? Do you have a specific tolerance you need to meet?

    Thanks.

  • 0 in reply to David Baba
    Prodigy 40 points

    Vin is 50-70 volts. (I know 70 is above the limit of LM5117 but I can use a LDO for Vin pin of LM5117) 

    Vout is 30 volts

    Iout depends on the installation. This is why I need load share. I am planning to pull 20A from a LM5117 using dual IPP075N15N3G mosfets for both high and low sides. For higher Iout I am planning to load share multiple LM5117 modules. 

  • 0 in reply to Oytun YILMAZ
    TI__Mastermind 40040 points
    Unfortunately you cannot use an LDO for the Vin, as the SW (and Boot) pin will see be subjected to a voltage that violates the abs max. I would like to present you a possible solution that may meet your requirements of 20A and your Vin of 70V. Please see the link of a schematic and approach that will work for your spec.

    www.ti.com/.../tidrce4.pdf

    If you can limit the input to 65V (not using LDO because of reasons stated above) then you can use the LM5119, which is probably the easiest approach to a solution.
  • 0 in reply to David Baba
    Prodigy 40 points
    Thanks for the suggestions. I guess I have to stick with the LM5116 if LDO is not an option.

    As far as I understand the design you provided works for 2 LM5116s at most. Am I right ?

    Also a quick question about gate charges of mosfets. I am planning to use 2 mosfets with gate charges 50nC. LM5116 has less Peak HO Source Current than LM5117. Which formula can I use to calculate maximum total gate charge of mosfets I can use ?
  • 0 in reply to Oytun YILMAZ
    TI__Mastermind 40040 points
    Suggest using the LM5116 Quick start calculator. Need to watch for The losses in the FET as well as the Current capability of the VCC regulator if you do not intend to use an external VCC bias supply?

    See link below to QS calc.

    www.ti.com/.../lm5116-5116wg-25116design-calc
  • 0 in reply to David Baba
    Prodigy 40 points
    Thanks a lot for the spreadsheet. It really helped me.

    One thing puzzled me is the "VCC Start-Up Current ICC (mA)". If I am able to supply voltage through the VCCx than why there is a startup current limit ? Is it because Vccx is assumed to be supplied from the output? I guess it is possible to supply Vccx from the input ?
  • 0 in reply to Oytun YILMAZ
    TI__Mastermind 40040 points
    Yes, you can supply VCCX externally. just make sure that VCCX>Vin. If ever there is a condition that this is the case, you will need to place a Diode at the Vin to the Vin pin of the device to block reverse currents. This is addressed in the datasheet (see Fig 26 in Datasheet).