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Original question:

ADS124S06: Can I use Constant Current Measurement for Two RTDs

UCC28600: UCC28600

ASHISH KUMAR SINGH
Prodigy 100 points
Part Number: UCC28600

Tool/software:

Subject: UCC28600 – Observed Burst Switching Behavior Not Matching Datasheet

Question:
Hello,

I am using the UCC28600 in my power supply design and I have observed a switching behavior that I would like clarification on:

  • In my measurements, the burst switching frequency is ~130 kHz, and the burst-to-burst frequency is ~1 kHz.

  • During this operation, the feedback (VFB) voltage cycles between 0 V and ~1.7 V.

As per the datasheet:

  • In burst mode, the expected burst frequency is around 40 kHz, and

  • The feedback voltage should typically be below 0.7 V.

Because of this, my observed operation does not seem to fit into either burst mode or frequency foldback mode (FFM) as defined in the datasheet.

Point right My question: Which operating mode of UCC28600 corresponds to this behavior?

Any guidance or explanation from TI experts would be very helpful also sugest posiible recomendation to resolve this problem.

Thanks,
Ashish

  • 0
    TI__Guru* 86266 points

    Hello,

     

    The transformer magnetizing inductance and transformer turns ratio set the max frequency the design operates at. If the transformer is not setup correctly it could cause the burst mode not operate at the frequency that you would expect it too.

     

    The other thing that could cause the design to not operate correctly is have the current sense resistor set to a value larger and/or smaller than it should be.

     

    The following link will bring you to an excel design tool that you can use to check the transformer’s magnetizing inductance, turns ratio and the designs current sense resistor.

    https://www.ti.com/tool/download/SLVC104

     

    Regards,