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LM5025: LM5025 Forward Converter (48V@0.8A) for POE Power Sourcing (PSE)

masahiko shimizu
Guru 11235 points
Part Number: LM5025

Hi,

My customer used TI designs PMP7840.
He liked this TI designs.
Currently, He need to design next their product.
Condition is 24Vin, 48Vout and 0.65A.
But PMP7840 can not accept input 24V.
He wants to use LM5025.

Could you tell me where we change design of PMP7840 for accept input 24V, please?

Best regards,
Shimizu

  • 0
    TI__Mastermind 31580 points
    Hi Masahiko-san,

    I have asked one of our engineers to respond to your post. You should see a reply later today.

    Regards

    Peter
  • 0
    TI__Intellectual 1550 points
    Hi Masahiko-san,

    Yes. LM5025 has no problem supporting 24VIN. To adapt the PMP7840 design to your input requirement, you would need to recalculate the following parameters:

    1. UVLO resistors
    2. RAMP RC values based on Eq 4 and 5 on page 19 of datasheet
    3. Recalculate the voltage stress of the main FET VIN/(1-D) and the current stress, see if you would need to change the FET. So does the diodes on the secondary
    4. Recalculate the dead-time and change the resistor on the TIME pin as needed
    5. Retune the compensation network parameters of the error amp
    6. If CBC is desired, CS1 would need to be used while CS2 would need to be grounded. See page 13 of datasheet

    Regards,
    Wangxin
  • 0 in reply to Wangxin Huang
    Guru 11235 points
    Hi Wangxin-san,

    Thank you for last time.
    I had a mistake.
    Customer is using LM5025C.

    Q1: Is your answer same even if customer uses LM5025C?
    Q2: What is the defference of LM5025 and 5025C?

    Best regards,
    Shimizu
  • 0 in reply to masahiko shimizu
    TI__Intellectual 1550 points

    Hi Shimizu-San,

    1. Yes.

    2. The difference between the two devices are summarized in the first paragraph of the description in the datasheet.

    Just make sure to use the parameters of LM5025C when you make calculations.

    Regards,

    Wangxin

  • 0 in reply to Wangxin Huang
    Guru 11235 points

    Hi Wangxin-san,

    Thank you for last support.

    I add questions about previous your answer about below.

    >5. Retune the compensation network parameters of the error amp
    >6. If CBC is desired, CS1 would need to be used while CS2 would need to be grounded. See page 13 of datasheet

    Q1: About No.5.
    Please see the attached file.
    Which part of circuit did you show about "the compensation network parameters of the error amp"?
    Could you show detail part at this circuit, plsease?
    -> Is it C17 and R19?

    Q2: Could you let me know the equation for calculation of the compensation network parameters of the error amp, please?

    Q3: About No.6.
    Please see the attached file.
    What do R38 and R39 mean?

    Q4: I think that R24 and C34 is filter. Is it correct?

    Best regards,
    Shimizu

    snvr213.pdf

  • 0 in reply to masahiko shimizu
    TI__Intellectual 1550 points

    Hi Shimizu-san,

    Q1: C41, C42, R41.

    Q2: No dedicated equations for loop compensation. Small signal modeling will be helpful. Normally, lab experimental tuning is needed with the frequency response analyzer.

    Q3: T1 is the current sensing transformer. The current is sensed on the primary side and get reflected to the secondary side and converted to a voltage signal through R38. I am not sure about the purpose of R39.

    Q4: I agree. But the corner frequency is high though, i.e., 1.59 MHz.

    Regards,

    Wangxin