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LM5175: 2-phase solution for higher current output

Mats Erik Setterberg
Prodigy 50 points
Part Number: LM5175
Other Parts Discussed in Thread: LM5176

Hello,

Currently i have a working design using the LM5175 buck-boost controller.

The design works great and are currently in production. 20V-30V input, 24V 10A output.

The next project that i will be starting very soon is a system with very similar spec, only the output current will be increased to 20A (maybe higher).

According to the LM5175 product page, the maximum output current for this controller is rated to 20A.

I stop by this forum from time to time to do some browsing, and i have noticed over time that a 2-phase solution is recommended when outputting higher currents.

As i already have a working design made for 10A output, it would be great in terms of development time and time-to-market to reuse the design and put 2 circuits in parallell.

And therefore my question: Is it possible to use the LM5175 in such a parallell configuration? Maybe in a simular way as suggested in this app-note from Linear Technology?

If yes; is there any documentation available containing guidelines to do this with the LM5175?

If no; what other solutions can you suggest that i can use to meet my system requirements?

Best regards

 -Mats

  • 0
    TI__Guru 73270 points
    I would suggest you to consider the LM5176. You can stay with your design but change the IC to the LM5176, and remember to adjust the RT resistor to keep the switching frequency at the same. There is also an article on how to parallel two LM5176 for higher power (click the link below), and currently we are working on a simplified version which will be published in a few weeks.

    www.ti.com/.../getliterature.tsp LM5176&tisearch=Search--Everything
  • 0 in reply to Youhao Xi
    Prodigy 50 points
    Hello Youhao,

    Thank you for your comments.

    Just to clarify, by switching to the LM5176 it would be okay to stay with a single-phase solution for 20A output? Or would you still recommend a 2-phase design?

    Any chance to get some hints in regards to the simplified 2-phase version you are working on?

    -Mats
  • 0 in reply to Mats Erik Setterberg
    TI__Guru 73270 points
    We currently did a 300W reference design with the LM5176. see the link below.

    www.ti.com/.../PMP21278
  • 0 in reply to Youhao Xi
    Prodigy 50 points
    Hello Youhao,

    Thank you. This will be of great help.

    How do you think this design will perform with 24V 20A output? (If inductor and FETs are adapted accordingly.
    Do you think 480W output power will be too much for single phase?

    -Mats
  • 0 in reply to Mats Erik Setterberg
    TI__Guru 73270 points
    For 24V 20A output, I will suggest you to parallel two LM5176. I am concerned about the integrated drivers that may not be able to drive more FETs efficiently than shown in the TIDA design.
  • 0 in reply to Youhao Xi
    Prodigy 50 points
    This was my concern as well when considering this design, but wouldn't that be solvable with external MOSFET drivers?
    Using the MOSFET drivers would lead to a much lower BOM cost compared to the 2-phase solution suggested above.

    Do you have any other concerns about the 24V 20A single phase design?

    Im mostly surrounded by software engineers, so i dont have anyone around me to discuss this with.
    Your thoughts are much appreciated.

    You also mentioned a simplified 2-phase solution that will be published in a few weeks.
    I need to keep an eye out for this. Where will this be published? Is there anywhere i can subscribe to get a notification when this is published?
    Can you give any more information regarding this simplified solution at this time?

    -Mats
  • 0 in reply to Mats Erik Setterberg
    TI__Guru 73270 points
    External driver can be a solution and you need two half bridge drivers. The external drive must be able to set dead-time. The LM5176 has internal adaptive dead time which will defeated if external drivers are used. In addition, single phase requires a larger inductor which may be more expensive than two smaller inductors for dual phase. You need to do a trade-off.