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SM72295: Buck-Boost design with SM72445

Frieder Rabl
Prodigy 120 points
Part Number: SM72295
Other Parts Discussed in Thread: SM72445,

Hi!

I'm working on a design with the SM72445 and SM72295.
Can the driver handle different mosfet types on high and low side? I'm thinking of optimizing the low side mainly on switching behaviour and give more focus on RDSon with the high side mosfets. Hence using different kinds in my design. Do I have to consider anything important when doing this?

Thanks!
Frieder

  • 0
    TI__Mastermind 23055 points

    Hello Frieder,

    Thank you for the interest in TI gate drivers for you application. I help support the SM72295 and can help with your general question on the MOSFET types.

    The SM72295 has 3A gate driver capability and can support different MOSFETs for the low side and high side. The possible concern to consider is that if the high side and low side MOSFETs have a different total gate charge, Qg, the Vgs rising and falling times will be different for the two different MOSFETs. You can adjust the gate resistance for the two MOSFETs to accommodate this however. If you are operating with short dead times from the low side and high side transitions, you should consider adjusting the gate resistors to achieve similar switching times.

    Let us know if this addresses your questions, or you can ask for additional information on this thread.

    Regards,

    Richard Herring

  • 0 in reply to Richard Herring
    Prodigy 120 points
    Hi Richard,

    thank you for your quick answer.
    The idea I hab behind this is that I use mosfets with low RDSon but slower switching behaviour for the high side, as they see the most of the current. And on the low side focus more on fast switching. If I increase the Gateresistance I loose this advantage I guess. Why is there a problem with using mosfet with different switching times?

    Regards,
    Frieder
  • 0 in reply to Frieder Rabl
    TI__Mastermind 23055 points

    Hello Frieder,

    Thank you for the response, and I understand the concern. I wanted to just point out something to confirm in the application. If you will have short dead time programming between the high side switching transitions and the low side switching transitions, I was suggesting to keep in mind the different MOSFET switching times. If you have adequate dead time, then this will not be an issue.

    Just confirm in the application, that there is dead time from the low side and high side MOSFET Vgs signals, that is the concern. If there is dead time then there should be no concern.

    Please confirm if this addresses the question, or you can always post more questions on this thread.

    All information in this correspondence and in any related correspondence is provided “as is” and “with all faults”, and is subject to TI’s Important Notice (http://www.ti.com/corp/docs/legal/important-notice.shtml).

    Regards

    Richard Herring