• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 62 subscribers
  • Views 498 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LM5122: LM5122 based SEPIC with output voltage over 100V

Anthony Trigiani
Prodigy 10 points
Part Number: LM5122
Other Parts Discussed in Thread: LM5156, PMP23320

Tool/software:

I am looking for a solution to implement a SEPIC with 200V output. The LM5122 looks like a promising option, and is even featured in the technical article in the following link with additional circuitry for a synchronous rectifier setup: https://www.ti.com/document-viewer/lit/html/SSZTCS1

The only issue is the SW pin is limited to 100V - but if I have 40V input on the SEPIC and 200V output, I could expect ~240V on the switched node if I connect it like in the schematic above, thereby putting an over-voltage on SW pin. My idea is instead of connecting the SW pin to the switched node, it could be connected to ground. The idea is I want HO to switch, but since it is AC coupled to the gate of Q1, the DC level of HO shouldn't matter. Looking at the block diagram, If the level shift circuitry can work at ground potential (no level shifting needed), I don't see an issue. My question is, will the LM5122 be adversely affected or behave bizarrely with the SW pin grounded?

If there is an issue with grounding the SW pin, is there another way to achieve an output over 100V?

Thanks,

Anthony

  • 0
    TI__Mastermind 31830 points

    Hi Anthony,

    Thanks for using the e2e forum.
    I agree that there is risk of damaging the device if SW voltage goes above abs max.

    Here my first question would be, if a synchronous design is necessary, or if a asynchronous SEPIC would also be possible. This would make the design more simple and removes any problems of a high side switch.
    LM5156 could be used for this case.

    If LM5122 is still preferred, I found a reference design for higher Vout levels (110V).
    https://www.ti.com/tool/PMP23320
    Here, the SW problem is avoided by creating a asynchronous design as well and not using the HO switch.

    Best regards,
    Niklas

  • 0 in reply to Niklas Schwarz
    Prodigy 10 points

    Hi Niklas, thanks for your response. Yes, I am looking for a synchronous design in order to improve efficiency. That is interesting with the PMP23320. On that design the switched node is grounded, but HO is simply not used. I suspect if one were to probe HO, it would likely be switching with the grounded SW pin as its reference. If that's the case, the LM5122 should work for my application.

  • +1 in reply to Anthony Trigiani
    TI__Mastermind 31830 points

    Hi Anthony,

    I agree that the HO should still put out a driver signal with constant reference to GND. Unfortunately, I did not find other reference designs which are closer to your design idea, so I can only confirm the functionality in theory.

    If there are any additional questions coming up during the design process or if a review of the first schematic draft is desired, please let me know.

    Best regards,
    Niklas