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LM5166: Is Fly-buck configuration OK?

Part Number: LM5166
Other Parts Discussed in Thread: LM25017, , LM5161, LM25180, LM5180

Hi,

Is LM5166 suitable for use in Fly-buck configuration (isolated output with 1:1 coupled inductor)?  I have a design which previously used the LM25017 in fly-buck to generate dual output (12V isolated, 12V non-isolated).  I have a new design which could benefit from the same configuration, but the design is using an LM5166 elsewhere on the board to generate a 5V rail.  It would be nice to use the same DCDC regulator twice.  It is also nice that the LM5166 is capable of higher efficiency in the 5V output configuration than the LM25017 would be.

If it is possible, any considerations I should know?  I am assuming it would need to be in COT mode.

Could the differences in current limit of the LM5166 vs LM25017 pose any concern?  The LM25017 doesn't list different current limits for the high-side vs low-side FET thresholds, but the LM5166 does.

Thanks for your help!

Robbie

  • Hi Robbie,

    The LM5166 is not Fly-Buck compatible as that requires:

    1. FPWM operation (to allow negative inductor current, particularly when the primary-side output is lightly loaded)).
    2. A negative current limit (to support OCP of the isolated output).

    Depending on the output current requirements, another option is the LM5161 (100V/1A converter).

    By the way, an alternative to the Fly-Buck topology is the PSR flyback converter (see the LM5180/1 and LM25180/3/4 family). However, if both primary and secondary referenced outputs are required, the Fly-Buck topology seems more suitable.

    Regards,

    Tim