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LM5100A: Two-Switch Forward Converter bootstrapped gate driver

tynmon
Prodigy 70 points
Part Number: LM5100A
Other Parts Discussed in Thread: UCC27714

The LM5100A  High Voltage High-Side and Low-Side Gate Driver datasheet indicates that the device is used with Two Switch Forward Power Converters. In this topology, both FETs are driven on and off at the same time. Is there a bootstrapping configuration for this device that would work with the Two-Switch Forward Converter given that both FETs are activated simultaneously?

  • 0
    TI__Intellectual 2805 points
    Hi tynmon,

    Thank you for your interest in the LM5100A device. Let us look into LM5100A's ability to work in a bootstrapping configuration that would work with the two-switch forward converter.

    regards,
    Mateo
  • 0
    TI__Mastermind 23155 points

    Hello tynmon,

    Thank you for your interest in the LM5100A for your application. I am an applications engineer with TI and will work to answer your questions.

    The LM5100A is suited for two transistor forward converters since the two driver inputs can be driven simultaneously. You question on the boot strap circuit is understandable since the switch node behavior is different than a bridge converter.

    The 1s consideration is; when the low side switch is on, before the high side starts switching, there is a path from the low side switch drain, thru the transformer winding to the switch node. So there is a charging path for the boot strap capacitor thru the transformer winding.

    Also there is a circuit you may want to consider that is in the UCC27714 datasheet that shows an external circuit to provide a charging path for the boot strap capacitor, when the low side switch is off. In section 8.4.3 is the operation with two outputs on simultaneously and the circuit is illustrated for the two transistor forward. In the case of the LM5100A, the resistor RBOOT will only be connected to the Mosfet gate since the LM5100A has the internal boot diode.

    Please confirm if this addresses your questions in the conversation thread.

    Regards,

    Richard Herring

  • 0 in reply to Richard Herring
    Prodigy 70 points

    The circuit in section 7.4.3 of the UCC27714 datasheet should work great for my two-switch forward converter. It may be a good one to include in the LM5100A datasheet.

    Thanks for the response.