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UCC27511: Does UCC27511 have a passive pull-down on the gate driver output pins ?

Matt Schurmann
Genius 11095 points
Part Number: UCC27511

e2e Gurus, 

Does the UCC27511 have a passive pull-down on its OUTH and OUTL pins? 

Is it recommended to add one externally to ensure the gate remains in a known state when the VDD pin supply is removed?

  • 0
    TI__Expert 4070 points

    Hi Matt,

    Thanks for reaching out!

    The UCC27511 has an active pull-up on the OUTH pin and an active pull-down on the OUTL pin as shown below.

    Therefore, the Output pins should not be externally pulled up or down.  Additionally, the Output is held low when the input pins are floating / undefined.

    I hope this helps!  If I answered your question, please press the green button, otherwise feel free to follow up!

    Thanks,

    Aaron Grgurich

  • 0 in reply to Aaron Grgurich
    TI__Genius 11095 points

    Hi Aaron,

    Not to be pesky. But my question here was about how to ensure the driver output is defined when the the UCC27511 VDD pin is low/floating. 

    I am debugging a customer design wherein they are powering off the VDD pin with the converter input voltage still high. If there's no passive pull down device on the output, it can float due to leakage. And even if the external pull down will add some loading, it would be needed to ensure the power device is OFF when the VDD pin of the driver is low.  

  • 0 in reply to Matt Schurmann
    TI__Genius 11095 points

    Answered offline. This device does not have internal passive pull downs on the driver output.

    Thanks for the help.

  • 0 in reply to Matt Schurmann
    TI__Expert 4070 points

    Matt,

    No worries!

     

    The UCC27511 has internal UVLO circuitry on the V_DD pin that holds the output low when the V_DD falls below ~3.9V.

    If the customer design can guarantee that the V_DD stays below the UVLO threshold, then they should be in the clear.

     

    Thanks,

    Aaron Grgurich

  • 0 in reply to Aaron Grgurich
    TI__Genius 11095 points

    Hi Aaron, The driver would still need VDD voltage to hold the driver output low. If VDD = 0V, the internal circuits do not have enough bias to control the output driver stage. In the block diagram, the output stage is shown as NMOS devices. Without VDD supply, the driver will not be able to raise the gate of these NMOS to keep the pull-down enhanced.  Anyway, I got confirmation offline, I'll ask the customer to add a 10k pull-down externally on the driver output to cover the case when VDD is low. Thanks.