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UCC2803-Q1: Upgrade from UCC2805 - Duty cycle limitation

franziskus
Expert 8369 points
Part Number: UCC2803-Q1
Other Parts Discussed in Thread: UCC2803

Tool/software:

Hi,

my customer wants to move from UCC2805QDREP (50% duty cycle) to UCC2803MDREP (100% duty cycle).

They fear issues on their flyback design that may be introduced due to the different duty cycle when it goes beyond 50%.

Do you have recommendations to limit the device to 50% or is this not an issue?

Best regards

  • 0
    TI__Intellectual 1090 points

    Hi,

    The swap is usually fine in Flyback converter.

    Things to consider:

    In CCM, when the duty ratio goes above 50%, sub-harmonic oscillations (SHO) can be seen. To avoid SHO, slope compensation circuitry can be used.

    The UVLO thresold is different in UCC2803. Make sure that VDD is above UVLO (verify the value of Rstart)

    As the duty limit is increased, make sure that the thermal calculations look fine.

    Best,

    Adhvaidh