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UCD9248: Problem with UCD9248 controller on my board

sam sam88
Prodigy 30 points
Part Number: UCD9248
Other Parts Discussed in Thread: PTD08D210W

I am using TI 's software Fusion Digital Power Designer to configure UCD9248. My hardware schematic is  same with the Xinlinx's KC705 board and program by XML file from this link

https://www.xilinx.com/support/answers/56811.html

BUT i have a problem:

my board are not stable and after about 1 hour some rails will drop and duty cycle be unstable.you can see in attached picture

anyone can help me which part have problem???

Thanks your attention.

  • 0
    TI__Genius 9845 points

    The loop design may be marginally stable. You can go to the Design section of the Fusion Digital Power Designer, change Compensation Mode from Auto Tune to Manual. Then you can manually adjust K, Q, Fz (Complex Zeros mode) or K, Fz1, Fz2 (Real Zeros mode) to stabilize the loop. 

    As a general guide, you can place Fz2 at LC resonant frequency, place Fz1 at half LC resonant frequency, and then tune K value.

    Regards,

    Zhiyuan

  • 0 in reply to Zhiyuan Hu
    Prodigy 30 points

    Hi
    first thanks for your attention
    but i have another question
    i need 1.8V 10A with PTD08D210W in output.
    so how can i calculate k,fz1 and fz2 and is there any equation ??
    and can the temprature is Effect on my problem? if yes why?



    Best regards

  • 0 in reply to sam sam88
    TI__Genius 9845 points

    You can get L and C values from PTD8D210W datasheet, page 12. The total C is the capacitance in the module and the capacitance on the board.

    The LC resonant frequency is 1/sqrt(2pi*LC), in Hz. 

    Temperature may have impact to stability because output capacitance value may have variation across the full temperature range. The feedback loop design should have enough margin to stay stable at different temperatures.  

  • 0 in reply to Zhiyuan Hu
    Prodigy 30 points

    i think my problem solved

    thank's for your attention

    best regards