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LM51581: vin 9v~60v, vout 38v/200mA or 20v/400mA

Chen Alex1
Genius 4085 points
Part Number: LM51581
Other Parts Discussed in Thread: LM5158, LM5176

Tool/software:

hi sir

old design use the TI MC33063AP

new spec is vin 9v~60v, vout 38v/200mA or 20v/400mA

LM51581 Is right solution>? or did you have any suggestion?

thanks

  • 0
    TI__Mastermind 19715 points

    Hello Alex, 

    Using the LM5158x should work for your application. 
    But 1.5A of inductor current will be a bit tough to reach. 
    Either use a pretty high switching frequency of about 1 MHz or switch to the LM5158.

    Please use the QuickStart calculator to find the solution that fits best for you.  

    Best regards
    Harry

  • 0 in reply to Harry Hofner
    Genius 4085 points

    HI Harry

    did you mean the  LM5158X can support the Buck- boost ?

    when Vin is 60v, the device buck to 38V out

    when Vin is 9v, the device boost to 38v out?

    thanks

  • 0 in reply to Chen Alex1
    TI__Mastermind 19715 points

    Hello Alex, 

    You mentioned that you would want to replace the MC33063AP with the LM51581. 
    Like the MC33063AP, the LM51581 can also just be used as an asynchronous converter with only one FET. 

    These devices cannot be used as a Buck-Boost controller, which would need two FETs as a minimum.

    Ao, in case of a standard Boost topology, it could boost upwards, but when the input voltage is higher than 38V, the input voltage would basically show up at the output as well. 

    To avoid that, you could use the LM5158X to create a Flyback or a Sepic topology with that controller. 
    These topologies can also convert downwards (but they do not really buck).
     
    Please see the datasheets for this device family regarding Flyback and Sepic
     
    Best regards
    Harry

  • 0 in reply to Harry Hofner
    Genius 4085 points

    hi Harry

    TI have any solution can meet my inquire?

    thanks

  • 0 in reply to Chen Alex1
    TI__Mastermind 19715 points

    Hi Alex, 

    Maybe I do not really understand what you want to achieve without any further description. 

    So far, I understand the following: When Vin is 9v, the application shall boost to 38V out. 
    When Vin is 60v, the device shall regulate down to 38V out. 
    It is NOT acceptable to dee an output voltage that is higher than 38V.
    Is this correct?

    So, as mentioned before: 
    Either use the LM5158x to drive a Flyback or a Sepic converter
    Or use a part of the LM5176 or LM5177x family to create a two or four switch Buck-Boost

    You can also have a look at the Webbench-Designer on our website and enter the input- and output parameters to get proposals which devices can be used. 

    Best regards
    Harry