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LM25116: ... Topology for 5V and 3.3V supply.

Daniel Bates
Prodigy 20 points
Part Number: LM25116

Hi, I need help with my Strategy, I have a basic buck regulator based on the LM25 series ;)

For a hopefully a more stable 5V and 3.3V I've designed to go down the route of having linear regs after a buck converter. Also, I want to connect the 5V rail in parallel to a USB backup source, I envisaged conflict if I connected 5V USB to a 5V buck regulator, correct me if I'm wrong.

Sanity check please!

Daniel

  • 0
    TI__Prodigy 700 points
    Hi Daniel,
    the LM25116 is a DC/DC buck controller (that needs external FETs). You may want to consider a Buck Converter with integrated FETs depends on the applications power / current requirements.
    Post regulation with LDO is fine but usually not needed for standard USB application. So the first LDO for 5Vout is probably not necessary and can come directly form the DC/DC converter. Using the 3.3Vout LDO behind the 5Vout is ok. Just keep all application current requirements in mind.

    Best Regards,
    Robert Loke
  • 0 in reply to Robert Loke
    Prodigy 20 points

    Hi Robert, thank you for confirming my thought on the integrated FET.

    In the circumstance you describe, to switch down to 5V then use a LDO for supplying 3.3V, would it be OK to supply aux power via USB in parallel with the 5V output of the buck regulator (after inductor / power stage)? In the case of the buck regulator itself loosing power in particular. Is there scope for the current to flow back through the power stage or the buck regulator itself, to ground?

    Regards,

    Daniel

  • 0 in reply to Daniel Bates
    TI__Prodigy 700 points
    Hi Daniel,

    if you like to use aux power from another source to back up the primary 5Vout buck output you will need a kind of OR-ing circuit. The simplest way would be diode connected that would block any reverse current. But the diodes will have some voltage drop you need to keep in mind. TI has special OR-ing ICs as well you may want to consider.

    Hope this helps.

    Best Regards,
    Robert L