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UCC256404: Feedback loop oscillation

PUSHPENDER
Prodigy 60 points
Part Number: UCC256404

Tool/software:

LLC Converter feedback loop not stable.docx

Pls see the Document for system details and Problam statement.

My CV Loop is fully stable but in CC Loop , whole system oscillates at 2.6Khz . Can someone suggest right approach to handle the situation as Both CC and CV loop are co existing in system with seamless transition. 

  • 0
    TI__Guru* 86266 points

    Hello,

     

    Your inquiry has been received and will be reviewed in the order that it was received.

     

    Regards,

  • 0 in reply to Mike O'
    TI__Guru* 86266 points

    Hello,

    I think the way you have your current loop setup it may be fighting your voltage loop.

    The following link will bring you to a reference design for an off-line battery charger that uses an LLC for the step-down converter.  The converter uses constant current constant voltage feedback loops on page 2 of the schematic.  This feedback is proven and I believe if you use this feedback methodology/circuitry your control loops will be stable and will not fight each other.  https://www.ti.com/lit/df/tidmd32a/tidmd32a.pdf

     

    The following link will bring you to an application note that describes how to design for constant current, constant voltage using a similar control mythology as used in the above reference design.  This information should help you compensate your constant voltage constant current voltage and current loops.  https://www.ti.com/document-viewer/lit/html/slla619

     

    I would also recommend using a network analyzer to compensate both the current loop and voltage loop.  To ensure that your design has greater than 45 degree of margin and greater than 3 dB of gain margin. 

     

    Regards,