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LM5117: Adaptive deadtime when outputs are isolated from output FETs

Adrian Delforge
Prodigy 100 points
Part Number: LM5117
Other Parts Discussed in Thread: UCC5304,

Tool/software:

How does adaptive deadtime control behave if the SW pin is not galvanically tied to the mid point of the FETs?  I am hoping to use opto-gate drivers (UCC5304) on both outputs of the controller to achieve a high voltage output of 800V with near identical time.   I will of course have a current sense on the bottom leg going to the controller 

I would prefer to set the deadtime to account for the small delays.

Working on the prototype now for a fast deployment and would appreciate feedback for tech support.

Best,

Adrian

  • 0
    TI__Guru 58171 points

    Hello Adrian 

    LM5117's adaptive dead-time function doesn't work in your configuration. Please consider adding RCD circuit like this at the gate driver input in order to adjust the dead-time. 

    -EL  

  • 0 in reply to EricLee
    Prodigy 100 points

    Hi Eric, 

    Thank you for the reply.  Had issue logging back into to read the post.

    I appreciate the delay circuit but that my question is referring to the adaptive control.

    How does the adaptive control operate when the current/voltage transitions are not actually those of the bridge FETs but rather the optos?

    If it is disabled and does not adjust dead time fine but I would like to know to prevent my personal recreation of the big bang.

    Best,

    Adrian

  • 0 in reply to Adrian Delforge
    TI__Guru 58171 points

    Hello Adrian

    LM5117's adaptive dead-time function doesn't work in your configuration. For example in FPWM mode, HO will be enabled ~ 72ns (typ) deadtime after LO-off. LO will be enabled ,~ 71ns (typ) deadtime after HO-off. 

    -EL