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UCC28951: design document of UCC28951

Bill Xu
Intellectual 1440 points
Part Number: UCC28951
Other Parts Discussed in Thread: UCC28950, LMG3650R035, LMG3650R025

Tool/software:

Dear Product line application engineer

do we have any document to help design PSFB power supply based UCC28951? thanks.

regards,

Bill 

  • 0
    TI__Guru 50190 points

    Hi Bill,

    Mike put this together SLUA560D  to help with the design process. The UCC28950 has a lot of application notes tied to it on ti.com and these all apply equally to the UCC28951.

    I hope this answers your question. 

  • +1 in reply to JCHK
    TI__Intellectual 1440 points

    Hi, JCHK

    thanks for supporting in here! I had SLUA560D on hand. 

    regards,

    Bill

  • 0 in reply to Bill Xu
    TI__Intellectual 1440 points

    Hi, JCHK

    I download the SLUC222E and try to use this Excel document to help design. I prefer use LMG3650R025 or LMG3650R035 as MOSFET. since these GaN MOSFET integrated gate driver. how should I fill the QA gate charger in the excel document? the datasheet of LMG3650R025 has no these parameters. thanks.

    regards,

    Bill 

  • 0 in reply to Bill Xu
    TI__Guru 50190 points

    Hi Bill,

    Glad to hear it!

  • 0 in reply to Bill Xu
    TI__Guru 50190 points

    Hi Bill,

    The Qa gate charge is just for helping to better estimate the power losses in the gate drive. It is not critical to the overall design. 

  • 0 in reply to JCHK
    TI__Intellectual 1440 points

    Hi, JCHK

    get it. another thing: my design has big difference compare with datasheet standard design. the main difference as below.

    1. in standard design, the controller in second side. in my design, the controller in primry side.

    2. in standard design,  the output lvoltage is less than input voltage. in my design, the outpur voltage is adjustable in range from 0~500V.

    3. the standard design use CT to sensing switching current, in my design, I use resistor to sensing switching current.

    4. in standard design, the MOSFET is legacy MOSFET, in my design, I use TI GaN MOSFET: LMG3650R025 or LMG3650R035.

    .....

    all this causes the SLUC222E has less helpful for my design.

    currently, I'm debug the PCBA board. I increasing input voltage from low to high to check circuit running and confirm the function is correct. for example, I set up input voltage to 40V and output voltage adjustable from 0~32V with 1A output current. the circuit can running and I can get the output meet my expected.

         however, I meet GaNMOSFET damaged issue when I increasing input voltage to ~120VDC and output to 99V/1A. then I have back to review the circuit. Could you please help me to review the schematic and fixed the issue? below is the schematic for review..

    Electrosurgical Unit Energy Platform.pdf

    here is my question:

    1. does the shimming inductor is good or not? what is the good value for shimming inductor?

    2. what is the best delay time for TAB and TCD? Tmin?DCM?

    thank you so much for supporting!

    regards,

    Bill

  • 0 in reply to Bill Xu
    TI__Intellectual 1140 points

    Hi Bill,

    To understand the issue better can you please provide details on following questions?

    1. Is it the primary side GaN FETs that is being damaged or secondary side?

    2. Please provide drain to source voltages of GaN FETs, output voltage and current waveforms during the damage.

    To answer your queries,

    1. does the shimming inductor is good or not? what is the good value for shimming inductor?

     This depends on the requirement you have, a higher shim inductor value will ensure ZVS for higher load range and will reduce the switching losses throughout the load range, but it will also increase the conduction losses. So, tuning is required to find out the optimum shim inductance based on your application.

    2. what is the best delay time for TAB and TCD? Tmin?DCM?

    The deadtime should be chosen to be enough for the FETs to charge/discharge its Coss fully and thus ensure the ZVS switching. The deadtime need to be tuned based on the Coss of the FETs selected and also minimum load till which the ZVS is desired. Optimum point to enable DCM for the converter will depends on the switching losses and conduction losses of the SR FETs throughout the load range. It is most suitable to get DCM mode enabled when switching losses crosses and become higher than conduction losses.

    Regards,

    Deepak K