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UCC2897A: How to maintain same output OCP level with UCC2897A under different line input

Wei-Hao Chen (TW-FAE)
Expert 3260 points
Part Number: UCC2897A
Other Parts Discussed in Thread: PMP5123

Hi team,

My customer is using UCC2897A and they followed the PMP5123 design completely in their system, but they had a issue with the inconsistent output OCP level under different line inputs condition. 

Is any method to achieve the line-compensation function to maintain the same output OCP level when line input changes? 

Thank you.

Best Regards,

Wei-Hao

  • 0
    TI__Mastermind 27135 points
    Hi Wei-Hao Chen,

    Thanks for your interest in UCC2897A. UCC2897A has an integrated cycle by cycle current limiting function. This monitors the primary side current however, not the output current. For the same output power load on the secondary side, the primary side current is lower at maximum Vin vs minimum Vin. The cycle by cycle current limiting function will not give you a consistent threshold for output overcurrent protection because the primary side current varies with the input voltage.

    What you can do is implement an external overcurrent detection circuit on the secondary side to pull the FB pin below 2.5V when an overcurrent condition is detected. This will result in a zero duty cycle.

    Best Regards,
    Ben Lough