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UCC256403: Startup problems with UCC256403

Bastien Bertrand
Prodigy 165 points
Part Number: UCC256403

Tool/software:

FTE_ET_TAD00793_A.pdf

LLC_DESIGN.pdf

Hi TI,

I would like to contact you because I'm just starting to manipulate my first LLC, and I'm having a few problems with UCC256403 in startup.

The controller starts up, but the MOSFETs short-circuit. I don't understand why, but I have a few questions to ask in response to this problem :

  1. Rgate it's very high, so the rise time is long, so i can make a short-circuit with primary MOSFETs.
  2. Voltage MOSFET ringing, so a snubber is essential.
  3. Other problems

I'll share you my schematic, and the datasheet of my transformer for help me to resolve this problems.

I hope you can help me and others with their future designs.

Thanks

Best regards

  • 0
    TI__Guru* 85616 points

    Hello,

    I am reviewing your inquiry and will get back to you shortly.

    Regards,

  • 0 in reply to Mike O'
    TI__Guru* 85616 points

    Hello,

    I reviewed your schematic and functionally it looks correct.  I don't see any issue with it.

    Your Rgate resistors are 10 ohms.  If VCC is 12 V you will have 1.2 A of driver current.  Depending on the gate charge (dQ) to get your through miller plateau I would think this would be enough gate driver current (Idrive) to drive most FETs.

    Idrive = dQ/dt

    dt = dQ/dt 

    If you find dt is > 100 ns I would use external gate drivers to speed up the turn-on and turn-off the FETs.

    If your FETs are failing it is due to over current and/or over heating.  I would check the ISNS capacitor resistor divider to make sure the FETs are being protected from and over current.   If this divider is not setup correctly it could be causing your FETs to fail.

    You should also check to make sure your FETs are not getting too hot with a thermal camera.  They may require additional heat sinking.

    The following link will bring you to an excel design tool that you can use to check your design; as well as, your ISNS resistor capacitor divider.

    You also want to make sure that your VCR capacitor divider is setup correctly as well.  

    https://www.ti.com/tool/download/SLUC675

    You could have layout issues.  The data sheet for the UCC256403 data sheet gives recommendations for layout that you can use to check your design.

    The following link will bring you to 180 W evaluation module/reference design with a proven layout.  You might want to study and compare it to your layout to see if there are any improves that you could make to your layout.  Please note that Layout review is not a service offered on the e2e.

    https://www.ti.com/tool/UCC25640EVM-020?keyMatch=UCC25640EVM&tisearch=universal_search

    It might be worth while for you to order and evaluate the 180 W evaluation module.  You can use it to compare critical signals and performance to your design.

    TI has a reference design library that you might find useful as well.  There may be a design that already meets your requirements that TI has already done, that you don't have to trouble shoot.  The designs have a proven layout and BOM.  The following link will bring you to it.  You just need to input and output power requirements and tool will find design that meet or are close to meeting your design requirements.

    https://www.ti.com/reference-designs/index.html

    There is also an application note title "UCC25640x LLC Resonant Controller Features Brief Overview and Bring up Guidelines" that you can find at the following link.  It gives instruction on how to bring up and LLC design safely and avoid issues similar to what you are having now.

    https://www.ti.com/lit/an/sluaaj7/sluaaj7.pdf

    There is also an application note titled "Most Frequently Asked Questions About the UCC25640x LLC Resonant Controller" that you will find useful.  You can find it at the following link.

    https://www.ti.com/lit/an/sluaal2/sluaal2.pdf

    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,