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UCC28634: Power management forum

Gangadhar P
Intellectual 380 points
Part Number: UCC28634

Hi,

We are Using the UCC28634DR, 85V-265V to 48.00V @ 1A.

In this we have used the  Transformer  EE16( Inductance B/W:1-2/L=328uH+/-10%) instead of EE20 (B65847 suggested by TI).

In this case my Output Voltage=0, and Voltage at Auxiliary Output(VDD PIN)=1.8V.

Please find the attached files for the reference.

Please provide solution for this AC-DC_Design_1A.pdfUCC28634D.docx.

Thanks & Regards

Gangadhar P

  • 0
    TI__Expert 8210 points

    Gangadhar P

    In the word document UCC28634D.docx you attached there is no mention on what the turns ratio between the primary, secondary and auxiliary windings are.  In the specification from the webench design that was generated the following turns were specified.

    • Primary side turns (Npri) = 42
    • Secondary side turns (Nsec) = 18
    • Auxiliary side turns (Naux) = 5

    This gives a Nps of 42:18 and Npa of 42:5.  Please verify that your custom transformer meets this design requirement.

    I also noticed that the wire gauge is not specified in your design.  I also recommend verifying that the wire gauge is sufficient for the current/power of your design.

    Best Regards,

    Eric

  • 0 in reply to Eric Faraci
    Intellectual 380 points

    Hi Eric,

    We have followed the same specification, as mentioned in Webench.

    Here only the difference is the EE16.

    Thanks & Regards

    Gangadhar 

  • 0 in reply to Gangadhar P
    TI__Expert 8210 points

    Gangadhar

    It sounds like there may be something in your design that is preventing proper startup. In section 8.3.1 (page 15) of the UCC28634 datsheet it explains that the HV pin acts as a current source to charge the VDD capacitor.  Once VDD reaches VDD(start) PWM operation begins.  Until VDD reaches VDD(start) the transformer has no impact on the operation of the design.

    I recommend you review your design to identify what is preventing VDD from being charged up to VDD(start).  Please verify that your design follows the recommendations in the webench design and datasheet, and that you don't have any additional load on VDD that prevents it from charging up to VDD(start).  Please note that the HV pin only supplies around 4 mA of current.

    Best Regards,

    Eric

  • 0 in reply to Eric Faraci
    Intellectual 380 points

    Hi Eric,

    Now we are getting the VDD 12.4V, but the VDD(start) min13V.

    again the Output Voltage is 0V.

    Thanks & Regards

    Gangadhar

  • 0 in reply to Gangadhar P
    Intellectual 380 points

    Hi Eric,

    We are getting VDD 13V and it is not Stable,it is  Varying in between 10V to 13V.

    Thanks & Regards

    Gangadhar

  • 0 in reply to Gangadhar P
    TI__Expert 8210 points

    Gangadhar

    Figure 16 (page 17) of the UCC28634 datasheet shows the expected startup behavior.  What happens is that VDD is trickle charged to VDD(start), where soft start begins.  During this startup the charged energy in the VDD capacitor powers UCC28634.  This causes VDD voltage to decrease. It's important that VDD voltage does not decrease below VDD(stop) during this mode, otherwise UCC28634 will shut down and restart the startup sequence. If this happens, you can slow down the voltage decay by increasing VDD capacitance.  Once soft start ends, bias power is provided by the aux winding, which allows VDD to regulate at the designed target.

    VDD(stop) has an abs max value of 8.5 V.  If the minimum voltage on VDD is 10V then it will not cause operation to stop.  UCC28634 can operate normally if the VDD voltage varies between 10 V to 13 V.

    If you still do not have any voltage on the output, but VDD is charging to VDD(start), we recommend you verify that there is not fault condition that is preventing startup.  All faults that UCC28634 measures are described in section 8.3.15 (page 41) of the datasheet.  In order for proper steady state operation, none of these fault events should trigger during startup or normal operation.  Some of these fault conditions can be caused by parasitic elements, such as non-ideal parameters of components or PCB layout which cannot be included in the webench design, so it's recommended you verify your design and modify it accordingly based on actual performance.

    Best Regards,

    Eric

  • 0 in reply to Eric Faraci
    Intellectual 380 points

    Hi Eric,

    We have changed the transformer, then VDD is charged up to VDD(start) 13V and  output is 45V (designed for 48V @1A).

    While testing with Load upto 190mA working fine. If the Load current is is 200mA then output is 0V and  VDD is again Trickle charging(VDD:min10V, max14.7V).

    Thanks & Regards

    Gangadhar P

  • 0 in reply to Gangadhar P
    TI__Expert 8210 points

    Gangadhar

    From what you provided it sounds like a fault condition is triggering when your output reaches 200mA.

    Table 3 on page 42 of the UCC28634 datasheet lists all the fault conditions that can cause UCC28634 to shut down.  I recommend you verify that none of these fault conditions are triggering as you increase power level.

    Best Regards,

    Eric