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LM5575: High Vin margin, split rail DC/DC solution

Satoshi
Guru 19645 points
Part Number: LM5575
Other Parts Discussed in Thread: LM5005, , LM5161, LM5017

I looking for below condition Split-rail DC/DC, is there recommended device?

(I finding LM5575 and LM5005, but these are not have application note, tool, and reference design)

-------------------------------------

・Vin：24V, margin is more than 75V. (75V Maximum rating is OK)

・Vout： ±15V

・Iout： Both 250mA

・Customer request is prepared application note, tool, and reference design, etc. 

-------------------------------------

Best regards,

Satoshi

  • 0
    TI__Mastermind 40040 points

    Hello Satoshi san,

     

    These devices will require you use one device for each rail, one being configured as a Buck and the other as a Buck Boost inverter configuration.  There are application notes on how to configure a buck device as a buck boost.  See attached.  The principles outlined in the application note can be applied to any buck regulator device.  

    Another alternative approach is to you a FlyBuck with +15V on the Primary and -15V on the secondary.  Please consider the LM5161 for the flyBuck application.  Or you can configure both rails on the secondary, see attached example of the LM5017 configured with two outputs that are on the secondary side.  I suggest using the LM5161.

    Hope this helps,

     

    David Baba.

    PMP9317_Dual15_Schematic.PDFa flyBuck with two outputs.

  • 0 in reply to David Baba
    Guru 19645 points
    David-san

    Thank you for reply.

    About LM5161, datasheet page-23 is described below;
    "The primary output voltage in a Fly-Buck converter should be no more than one half of the minimum input voltage."

    I think that 24Vin⇒±15Vout is not match above condition, is it correct?
    Or, is this Vin/Vout spec is not relation above condition?

    Best regards,
    Satoshi
  • 0 in reply to Satoshi
    TI__Mastermind 40040 points

    Hello Satoshi san,

     

    The Vin = 2 x Vout is a guidance for good load regulation.  When the guidance is violated the load regulation on the secondary will suffer particularly if the load on the primary and secondary are dissimilar. 

     

    In order to get around this issue you can do one of two things.

    1. Use a FlyBuck Boost.  this means you have -15V on the primary and +15V on the secondary using a 1:1 turns ratio transformer.

    2. Regulate Primary to 7.5V and use a 1:2 turns ratio transformer, as the example I provided.

     

    Hope this helps?

     

    Kind regards,

     

    David.