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TI Home » TI E2E Community » Support Forums » Power Management » Non-Isolated DC/DC » Non-Isolated DC/DC Forum » Current sensing of LM25117
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Current sensing of LM25117

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soo lee84680
Posted by soo lee84680
on Aug 09 2012 16:36 PM
Prodigy190 points

I try to use LM25117 for high input voltage POL, but using Rs between bottom FET source to GND is costly.

So I am wondering if LM25117 can allow CS pin connects to SW pin to sense bottom FET Rdson instead.

Please advise me, Thanks.

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  • EricLee1880267
    Posted by EricLee1880267
    on Aug 09 2012 16:44 PM
    Verified Answer
    Verified by EricLee1880267
    Expert5410 points

    Hi Soo

    Unfortunately, LM25117 is not designed for Rdson sensing which requires to connect CS pin to SW. Please check LM25116 which allows Rdson sensing.

    http://www.ti.com/lit/ds/symlink/lm25116.pdf 

    Regards,

    Eric

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  • soo lee84680
    Posted by soo lee84680
    on Aug 09 2012 17:30 PM
    Verified Answer
    Verified by soo lee84680
    Prodigy190 points

    Hi Eric,

    I have more questions on LM25117.

    The IC has CM pin, so can this pin be used for current share of modules used this IC?

    In adjustable output  design, OCP range turns out wide range, so can any compensation voltage signal be added to CS pin to minimize this error?

    Thanks.

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  • EricLee1880267
    Posted by EricLee1880267
    on Aug 09 2012 18:10 PM
    Verified Answer
    Verified by EricLee1880267
    Expert5410 points

    Hi Soo

    Usually, current sharing between multiphase modules can be done by sharing COMP (Please refer LM5119).

    CM can be used as a portion of your current sharing circuit, but CM itself doesn't have any feature to make the current sharing happened.

    There was an idea which compensating current limit variation by changing RAMP signal dynamically, but I have not tried yet.

    Regards,

    Eric 

     

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