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  • TI Thinks Resolved

LM27222: Driving 2 N-Channel Fets switching a load of 18 Amps at 30 HZ

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Replies: 5

Views: 77

Part Number: LM27222

What guilde lines should I follow to select the bootstrap capacitor for a LM27222 driving 2 N-Channel FETS switching a 18 AMP load at 30HZ? This is to use the LM27222 as a replacement for the LM2726.

  • Hi Randy,

    Thanks for your interest in our device, my name is Mamadou Diallo, I will help answer your questions.

    A good start would be determining your duty cycle. Bootstrap circuit technique is limited by the required duty cycle as it cannot achieve very high duty cycles given that the bootstrap capacitor needs to replenish during the low-side FET ON-time. Too long of high-side FET ON-time will cause the gate voltage supplied by the bootstrap cap to fall below the high-side FET threshold.

    A second item to determine is your total high-side gate charge to determine your gate capacitance and sizing the the bootstrap capacitor accordingly. The app note below further discusses in detail how to select these components.
    www.ti.com/.../slua887.pdf

    Please let us know if you have further questions or press the green button if this addressed your question.

    Thanks.

    Regards,

    -Mamadou
  • In reply to Mamadou Diallo:

    Rbias selection method?
  • In reply to Randy Craft:

    Hi Randy,

    Rbias is strictly optional. It is there for protection against transients current from the supply.

    Given that this device is a 6.85V(Max Recommended Operating Conditions), you may use values between 0-5Ω in series with the bias supply and VDD pin.

    Regards,

    -Mamadou
  • In reply to Mamadou Diallo:

    What device would TI recommend instead of the LM27222 as a replacement for the LM2726, if footprint-compatibility is NOT a constraint?

  • In reply to Randy Craft:

    Hi Randy,

    UCC27282 is our latest half-bridge driver, it is rated for -40C to 125C, includes a 5V UVLO and offers better drive current and switching characteristics.

    The devices below are a good starting point.

     

     

    UCC27282

    TPS2838

    TPS28225

     

     

     

    Order now

    Order now

    Order now

    Online datasheet

    Online datasheet

    Online datasheet

    Datasheet

    Datasheet

    Datasheet

    Tools & Software

    Tools & Software

    Tools & Software

     

     

     

    Number of channels (# )

    2

    2

    2

    Power switch

    MOSFET

    MOSFET

    MOSFET

    Bus voltage (Max ) (V )

    120

    29

    24

    Peak output current (A )

    3

    4

    6

    Input VCC (Min ) (V )

    5.5

    10

    4.5

    Input VCC (Max ) (V )

    16

    15

    8

    Rise time (ns )

    12

    10

    10

    Fall time (ns )

    10

    10

    5

    Prop delay (ns )

    13

    20

    14

    Iq (uA )

    2

    425

    350

    Input threshold

    TTL

    TTL

    TTL

    Channel input logic

    TTL

    CMOS

    TTL

    Negative voltage handling at HS pin (V )

    -10

    0

    0

    Features

    Enable and Interlock

    Dead Time Control

    Synchronous Rectification

    Synchronous Rectification

    Rating

    Catalog

    Catalog

    Catalog

    Operating temperature range (C )

    -40 to 125

    -40 to 125

    -40 to 125

    Package Group

    VSON | 10

    HTSSOP | 16

    SOIC | 8

    SON | 8

    Approx. price (US$ )

    1.40 | 1ku

    1.55 | 1ku

    0.59 | 1ku

     

    What application is this application/EE for?

     

    Please let us know if you have further questions.

     

    Regards,

     Mamadou Diallo

    High Power Drivers Applications and Technical Support

     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).

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