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TPS23754: TPS23754PWPR

Part Number: TPS23754

Hi,

We had followed a reference circuit design and got feedbacks for a 24V output POE+ circuit. We want to change the output from 24V to 28V. What are the changes that needs to be done. One obvious change we see is the feedback resistors. Any thing else in the circuit that needs to be changed to get a 28V output.

Attaching the schematic used for 24V output.

Thank you.

  • Hi Sunil,

    After you adjust the feedback resistor, check for stability. If re-compensating the loop is necessary, then see section 2.8 of our design guide: www.ti.com/.../slva305c.pdf

    Check that your current sense resistor is sized appropriately so it does not terminate the duty cycle if primary side peak current gets too high due to the longer duty cycle (section 2.6.8)

    The voltage ratings on Q1 & D14 should be fine since you are starting with a 24V design, but be sure to check Vds during testing.

    During testing, if your Vc voltage gets too high during startup or operation, then consider increasing R37 to reduce voltage.

    Regards,
    Tom Amlee
    PoE PD Apps Engineer
  • Hi Tom,

    Thanks for the suggestion.

    What would be the recommended resistor values that needs to be changed from the 24V design to get the 28V output.

  • Hi Sunil,

    Try reducing R32 to 4.02kohms & keep R31 the same.

    Thanks,
    Tom Amlee
    PoE PD Apps Engineer
  • Hi Sunil,

    Has your question been answered to your satisfaction? If so please click the green "resolved" button on the post you found most helpful. If you are still working on your issue, then feel free to respond & we can continue providing support.

    Thanks,
    Tom Amlee
    PoE PD Apps Engineer