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UCC28951: Troubles Getting to Steady-State

William Mcknight
Intellectual 380 points
Part Number: UCC28951
Other Parts Discussed in Thread: TINA-TI

Tool/software:

Hello,

I've attached the file I'm using to simulate as well as the google design sheet provided by TI.

A couple of specs:

Pout = 500W

Vout = 400VDC

Vin = 410VDC

I've used the excel sheet to get started and tried not to change a lot in the provided tina-ti simulation. 

I've got no-load attached to the secondary. To make sure it regulates I've used a very slow controller that should easily regulate with no load, yet it doesn't.. Some insight into why I'm having difficulties would be great. I've used suggested values from the excel sheet and designed the converter for somewhere between Vout_max and Vout_min.

If you could look into the file and see why the converter is not regulating even with such a slow loop, that would be great.

7115.SLUC222D.xls

slum277a_WillEdit.TSC

  • 0
    TI__Guru* 86266 points

    Hello,

    Your inquiry is under review.

    Regards,

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

    Hello,

    I reviewed the excel design tool and it looks like your voltage loop is crossing over at 150 Hz with less than 10 degrees of phase margin.  This could be your issue.  I would suggest that you re-compensate the voltage loop to have 45 degrees or more phase margin.  This can be accomplished by selecting Cz, Cp and Rf based on the tool recommendations within +/- 10%.

    The SLUC222D excel tool was generated based on application note SLUA560 which you can find at the following link.  You may find this information useful in your design process.

    https://www.ti.com/lit/pdf/slua560

    Thank you for interest in Texas Instruments (TI) products.  If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

    Regards,