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LM5177: LM5177: this design is workable for multiphase buck boost?

Xavier Lin
Prodigy 40 points
Part Number: LM5177
Other Parts Discussed in Thread: PMP7837, LM5122

Two LM5177 use the same COMP to make inductor current close.

Use an external voltage follower conntected one COMP pin to overlay the other COMP pin.

  • +1
    TI__Genius 17655 points

    Hello Xavier,

    Thanks for reaching out to us via e2e.

    Although the LM5177 has not been explicitly designed for Multiphase operation, it is possible to connect two or more of these vontrollers.
    Multiphase operation has been successfully tested by connecting two EVMs.

    Here is a concept how to connect the two controllers.

    The clock synchronization of two or more phases needs to be generated externally.
    For two phases you need to feed two clock signals with 180° phase shift into Sync1 and Sync2.
    For more phases you need more clock signals with the corresponding phase shift, e.g. 3 * 120°.

    The layout is very important for a good distribution of the power between the phases.
    The high current input- and output paths of all power stages must be connected in a star topology with similar (parasitic) inductances of these paths.

    Best regards,
    Harry

  • 0 in reply to Harry Hofner
    Prodigy 40 points

    Is it OK that directly connecting two LM5177 "COMP" pin?
    Since "COMP" is the ouptut of error amplifier, I can't sure "COMP" will follow which one error amplifier output.

    I saw PMP7837 has the same concept about connecting "COMP" together.

    However, I still curious why this is no promble to connect two error amplifier output?

  • +1 in reply to Xavier Lin
    TI__Genius 17655 points

    Hello Xavier,

    The COMP pins can only be connected directly, if the controller IC is internally using a transductance amplifier as error amplifier (which is driving a current at its output).
    Nevertheless, this concept of paralleling multiple controllers in that way cannot be used for any part with transductance amplifier, because there are other things which need attention.
    The LM5122 has especially been designed for Multiphase applications. When you look into the datasheet of that part, you will find five or six points listed which will work differently, when the part is configured as secondars device.

    Therefore, please contact TI first to find out if and how two controllers can be connected for multiphase operation.

    Best regards,
    Harry