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LM51231-Q1: Isolated Boost Convertor IC

Ananthu Mohan
Prodigy 60 points
Part Number: LM51231-Q1
Other Parts Discussed in Thread: LM5155, LM5156

Tool/software:

Hi,

I'm currently using LM51231QRGRRQ1 IC to convert Voltage input of (8-36V) to 48V Output for PoE application (30W).

But in order to conform to the IEEE 802.3 specification, we need to use an isolated Boost before supplying to the PSE module.

Could you please suggest a suitable TI part / solution for this application?

Thanks,

Ananthu

  • 0
    TI__Mastermind 32690 points

    Hi Ananthu,

    Thanks for using the e2e forum.
    If isolation is required, I would recommend an asynchronous Flyback topology approach. This should also be sufficient for a 30W application.

    The device I would recommend is LM5155 or LM5156. Both are suitable for this application.

    Best regards,
    Niklas

  • 0 in reply to Niklas Schwarz
    Prodigy 60 points

    Hi Niklas,

    Thanks for your prompt reply.

    I tried to simulate the LM5155 & LM5156 (isolated) on the TI web bench designer for my requirements.

    But it shows an error like " Design update failed. This design is not stable due phase margin either smaller than 35 or greater than 120"

    The simulation works only when I increased the input voltage to 15V (from earlier 8V) or If I changed the output current to 48V 0.1A (from earlier 0.65A).

    Could you please let me know if there are anyother parameters where I can change to make this regulator work for my requirements?

    Regards,

    Ananthu

  • 0 in reply to Ananthu Mohan
    TI__Mastermind 32690 points

    Hi Ananthu,

    Thanks for the feedback.
    It seems like webench struggles to auto-generate a suitable compensation for these design specs.
    However, from a system perspective, this design is definitely feasible.

    Instead of webench, I would recommend to use our quickstart calculation tool, which uses more inputs and therefore gives more possibilities to customize the schematic.
    https://www.ti.com/tool/download/SNVC240

    I also checked for reference designs using LM5155.
    Here are two examples which does not perfectly match the specs, but can still be used for reference:
    https://www.ti.com/tool/PMP22764

    https://www.ti.com/tool/PMP22800

    Please let me know if further design help is required.

    Best regards,
    Niklas