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LM25118 and LT3757A

Kai Hsiao
Guru 12675 points
Other Parts Discussed in Thread: LM25118, LM5118, LM5022, TPS40210, PMP, LM5122

Dear Sir

LT3757A could use SEPIC structure to do buck-boost 5.5V~36V to 12V/2A ,Does TI have any reference design can replace LT3757A  by SEPIC structure?

I also see LM25118's reference design can do 4V~36V to 12V/3A ,but LM25118 need to use more MOSFET and Diode 

What's the main different or benefit between LM25118 and LT3757A ,seems like both of them can do the same thing

  • 0
    TI__Intellectual 1435 points

    Thank you for the inquiry.

    Your 24W DC-DC converter requirement could be satisfied by a flyback, SEPIC or buck-boost topology.    The main advantage of the buck boost (LM5118) is the single winding magnetic element (simple inductor).   Inductors can be smaller and cheaper than transformers or coupled inductors.    The LM5118 would be a good choice if the system operates normally in step down (buck) mode with Vin > 12V.  If step-up is a common condition, then SEPIC  is a better choice.   

    TI offers multiple controllers that could replace the LT3757A in a SEPIC topology.   The LM5022 and TPS40210 are two popular devices.  If you check the product folder of these devices  on www.ti.com , you will find multiple SEPIC reference designs with PMP numbers in the Tools & Software tab.   A TPS40210 SEPIC example is PMP4608.  An LM5022 SEPIC example is PMP7305. 

    For higher efficiency, the LM5122 boost converter has been used in  synchronous flyback and  synchronous SEPIC designs.  A second FET replaces the rectifier diode to reduce power losses.