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UCC28740: Simplis AC simulation

Koon Hung Lee
Prodigy 250 points
Part Number: UCC28740

Hi,

I download UCC28740 Simplis model and add AC source, POP trigger (connected to vgate) and Bode plot probe. Unfortunately, my AC simulation doesn't converge. Could you help me? I have attached my file.

Thanks,

Koon

UCC28740_AC.zip

  • 0
    TI__Mastermind 40030 points

    Hello Koon,

    Thank you for your interest in the UCC28740 flyback controller. 

    I suggest that you may want to delete the POP trigger from your file.  This device tries to find periodic operating point and the controller does not have any repetitive periodic mode to find.  Not only does the UCC27840 include frequency dithering (which automatically varies the switching frequency), but the Quasi-Resonant valley-switching operation requires waiting for the next available valley to turn on the MOSFET.  This timing may not be an exact match to deliver the cycle energy to the load at a perfect equilibrium, so the feedback loop will continuously shift around the frequency to average out the energy delivery. 

    Removal of the POP trigger may allow your simulation to run. Please try it.

    Regards,
    Ulrich 

      

  • 0 in reply to Ulrich Goerke
    Prodigy 250 points

    Hi Ulrich,

    In order to perform AC analysis, I have to have the POP trigger. If I remove the POP trigger, I will get an error message asking me to add POP trigger.

    Koon

  • 0 in reply to Ulrich Goerke
    Prodigy 250 points

    Hi Ulrich,

    In order to perform AC analysis, I have to have the POP trigger. If I remove the POP trigger, I will get an error message asking me to add POP trigger.

    Koon

  • 0 in reply to Koon Hung Lee
    TI__Mastermind 40030 points

    Hello Koon,

    I have tried several different changes to try to get the POP to work and all of them failed.
    I think that the UCC28740 simply cannot achieve a repeatable set of waveforms that satisfy the POP and so AC analysis can't be done with this Simplis model.

    Perhaps you can obtain sufficient information about phase margin doing a series of transient analyses.

    Regards,

    Ulrich