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LM5022: Reference design ASAP

rmalcovich
Prodigy 100 points
Part Number: LM5022
Other Parts Discussed in Thread: LM51551, PMP9282

I am looking ASAP for a reference design of isolated DC/DC 5V input, 3.3V with 2.5A output.

Readily made bricks I found in this range, are ridiculous expensive (>20$) so we are trying to settle a design for our future product.

The most closest reference design will be this one, using LM5022, but the problem is that minimum input is 6V and we need 5V

http://www.ti.com/tool/PMP9282 

The big question is: can we replace the buck with one that accepts 5V on input?

Thanks in advance.

  • 0
    TI__Genius 17520 points

    Hi,

    You can design a flyback converter which allows you to do a step-down operation to what you need. If you cannot use the LM5022 because of the minimum input range, I would recommend using the LM51551 (since you will need hiccup-mode) in a flyback converter. It's minimum operating range is 3.5V, which is within your limitations.

    Datasheet is attached: http://www.ti.com/lit/ds/symlink/lm5155-q1.pdf

    Please see the design guide if necessary: ti.com/lit/an/snva866/snva866.pdf 

    With the LM51551, it looks like the power-stage should be quite similiar to the current design in PMP9282. Please let me know if you have any questions. 

    Thanks,

    Richard

  • 0 in reply to Richard Fu22
    Prodigy 100 points

    Hi Richard,

    Thank you so much, this is exactly what we need (perhaps not 4A)!

    Now in snva866.pdf the transformer part number is wrong, I cannot find at Wurth this, nor at Digikey or others.

    What do you think, this one is a good replacement?

    PA3855.004NL  (9..38V input + 10V aux, 2x3.3V output)

    productfinder.pulseeng.com/.../P719.pdf

    Thank you! 

  • 0 in reply to rmalcovich
    TI__Genius 17520 points

    Hi,

    You should be able to use the transformer, but I would make sure that at a lower input voltage, your ripple current is not high enough to saturate the transformer. To be safe, I would recommend talking to the transformer vendor to double check and see if they have better solutions. 

    Thanks,

    Richard