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Original question:

UCC28740: The switch frequency for UCC28740

UCC28740: Simulation error refer to PMP41031

Beida Song
Intellectual 830 points
Part Number: UCC28740
Other Parts Discussed in Thread: PMP41031, , PMP

Tool/software:

Hi Expert,

Customer design the schematic based on our PMP41031 reference design. But they meet an error when they simulate the schematic by SIMPLIS software. Could you give a support?

  • 0
    TI__Guru* 86286 points

    Hello,

     

    I checked the simplis model for the UCC28740 and it works without issue.  The PMP41031 is a released reference design with schematic and test data.  So, you have a good start with a working reference design and working model.  https://www.ti.com/lit/zip/slum672

    The schematic you have looks to be a two switch flyback.  You might be having issues because of initial conditions are not setup correctly in all of your components of your model.  Also, the schematic may have issues converging because of all the components being used.

    I would suggest to start off by modifying the existing simplis with minor modifications to support the input and output power requirements.   This should require changing the transformer turns ratio, input and output capacitance, feedback components and current sense resistor.  I would not add driving the high side FET since this will only complicate the model.  Also, you should not require the discrete driver formed by Q4 and Q6.

    The more complicated you make the model the greater chances you have convergence and simulation errors.  To save time we recommend that you start off with the simple release model that is debugged to save time.  Then you modify the power stage based on your design requirements.  Then you add more complex circuitry gradually to debug an evaluate if you desire.  

     

    Regards,

  • 0 in reply to Mike O'
    TI__Intellectual 830 points

    Hi Mike,

    Thanks for your support. Customer hasn't enough experience to do it well. Could you help make a design simulation model based on UCC28740?

    The requirements as below:

    1. Input voltage is 300~1500V, DC;
    2. Output voltage is 24V(diode voltage is 1V);
    3. Max Output ripple is 150mV.
    4. Typical Output current is 15A.
    5. Efficiency is 85%;
    6. Max switch frequency is 32kHz. Double MOSFET in fly-buck topology, Vds of MOSFET is 1700V, output cap is 47pF, Vgs is 4V. Isolated gate driver for high side MOSFET.
  • 0 in reply to Beida Song
    TI__Guru* 86286 points

    Hello,

     

    Simulation is not the easiest of things to do and can take a lot of time.  If the customer requires simulating a design it is their responsibility to simulate and debug the design.  To save the customer time we provide debug working models.  If the customer has questions in regards to issues they are having during this process, we can make suggestions on how to resolve them.

    In this case the customer has a working PMP design and a working model.  With the recommendations given, they should be able to modify the working model to be similar to the PMP design for simulation purpuses.

    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,

  • 0 in reply to Mike O'
    TI__Intellectual 830 points

    Hi Mike,

    Let me feedback customer.

    Another question: for customer's application, does TI have better design reference with simulation model?

  • 0 in reply to Beida Song
    TI__Guru* 86286 points

    Hello, 

    We have power supply design services (PDS) team that does the PMP reference designs.  When they release these designs they have schematics, test data and layout files.  To get the designer started.  Presently these PMP files do not have simulation files to go with them. 

    TI has released Tina, Simplis and PSpice models are generally done on EVMs.  The customer can modify these files to simulated their designs.

    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,

  • 0 in reply to Mike O'
    TI__Intellectual 830 points

    Hi Mike,

    Thanks for your support. Customer hasn't enough experience to do it well. Could you help make a design silmulation model?

    The requirements as below:

    1. Input voltage is 300~1500V, DC;
    2. Output voltage is 24V(diode voltage is 1V);
    3. Max Output ripple is 150mV.
    4. Typical Output current is 15A.
    5. Efficiency is 85%;
    6. Max switch frequency is 32kHz. double mosfet in fly-buck , Vds of MOSFET is 1700V, output capable is 47pF, Vgs is 4V. Isolated gate driver for high side MOSFET.
  • +1 in reply to Beida Song
    TI__Intellectual 830 points

    Hi Mike,

    As you suggested, customer to test UCC28740 with a PCB. They find that CS trigger protection. The test condition is below: Vin = 350V, Vout=24V, load=0.7A. Could you help give trouble screen suggestions? The schematic is the same as UCC28740 simulation file.

  • 0 in reply to Beida Song
    TI__Guru* 86286 points
     

    Hello, 

    We have power supply design services (PDS) team that does the PMP reference designs.  When they release these designs they have schematics, test data and layout files.  To get the designer started.  Presently these PMP files do not have simulation files to go with them. 

    TI has released Tina, Simplis and PSpice models are generally done on EVMs.  The customer or you can modify these files to simulated their designs.

    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,

  • 0 in reply to Beida Song
    TI__Guru* 86286 points

    Hello,

     

    In regards to the design having issues working.  The following link will bring you to an excel design tool that can be used to check the design.  I would start with this tool to check the design.

    https://www.ti.com/tool/download/SLUC487

     

    If no errors are found and the design is shutting down sporadically it could be due to aux winding noise or CS noise triggering a fault.  If this is the case it can be removed by filtering and snubbing.

     

    The following link will bring you to an application note that describes how primary fault sensing that the UCC28740 uses works.  The issue with it and how to resolve them with filtering and snubbing.  This should help you resolve your startup and regulation issues if it is related to current sense or aux winding noise.

    https://www.ti.com/lit/an/sluaac5/sluaac5.pdf

     

    Regards,