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LM5118: Using LM5118 in Boost Only Topology

Phil Salisbury
Prodigy 240 points
Part Number: LM5118

I have a working design for a buck-boost topology based on LM5118.  I am considering changing this to boost only and I am interested to know if the LM5118 would work in boost only mode if I eliminited the high side MOSFET and associated diode.

Thanks

Phil

  • 0
    TI__Mastermind 42251 points

    Hi Phil,

    thank you for using the E2E forum.

    Basically this should work if you ensure that you do not enter the buck-boost area (D < 69%)

    Have you already tried this on one of your boards?

    I will further investigate if there is something limiting and come back to you in 2-3 days.

    Best regards, 

     Stefan 

  • +1 in reply to Stefan Schauer
    Prodigy 240 points

    I want to get the TI opinion on it before trying it as I only have a few first articles right now so I don't want to fry an LM5118.

    The circuit is boosting 24V input to a DAC variable 26 to 32V output.

    Thanks

    Phil

  • +1 in reply to Phil Salisbury
    TI__Mastermind 42251 points

    Hi Phil,

    i checked again -  unfortunately this does not work:

    The LM5118 uses emulated current mode and senses the inductor current through the current sense resistor that is in series with the the recirculating diode. The circuit won't work correctly if "the high side MOSFET and associated diode are removed" and the inductor is connected to VIN: The dc or offset component of the inductor current won't be captured without the current sense resistor and operation will be erratic at best and without current limit.

    Best regards,

     Stefan