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LM25183: LM25183 Inquiry

Ray Vincent Aranzaso
Mastermind 18180 points
Part Number: LM25183
Other Parts Discussed in Thread: LM25184, LM5180

Hi,

Good Day. I have a customer who is working with LM25183. Please see below his query for your reference. Thank you very much.

I have questions about LM25183 and the associated Transformer. I am taken Vin of 10-27V and creating a flyback converter to get 5V with 1.5A.
I'm looking at the pcb recommended layout and comparing to mine. My transformer is Coilcraft ZB-1051AE

I have hooked up the transformer per the LM25183 recommendation with VIN of LM25183 connected to Xfmr pins 3 and 4 (which are the combined negative terminals of the xfmr). The SW pin of LM25183 connectos to Xfmr pins 1 and 2 (which are the combined positive terminals of the xfmr).
But I realized things looked flipped on my layout compared to LM251583 Eval pcb
Compare the polarity of the xfmr in the LM25183 datasheet to eval datasheet. The Eval has xfmr is flipped. But it should still work as the polarity on the secondary is 180 degree opposite, so as long as that is maintained we should be okay. Right?

Best Regards,

Ray Vincent

  • 0
    TI__Guru 73102 points

    Hi Ray,

    Please follow the LM5180/LM25184 PCB layout guidance.

    Note the dot polarity of a flyback is different to that of a forward converter (as only one winding conducts during a given interval for a flyback, e.g. the primary winding conducts when the FET is on, and the secondary winding does not conduct during this time). If both windings have their dots flipped, then the relative polarity configuration from a primary-to-secondary standpoint remains consistent.

    See app note SNVA805 for more detail and also this power supply design seminar: https://www.ti.com/seclit/ml/slyp494/slyp494.pdf

    Regards,

    Tim