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LM5158: Customize LM5158RTER ‑ 10V-60V to 12.00V @ 1A Design for isolation

Yetkin Serimer
Prodigy 30 points
Part Number: LM5158

Tool/software:

I want to design an isolated power circuit with a 10–60V input and 12V output. When I use Webench the attached design seems suitable, but here the input GND and the output GND are the same. I think this would break the isolation. I’m not very experienced with power circuit design. For that reason I want to ask: on the LM5158, the AGND and PGND pins — are those grounds tied together? Should they be connected here? In the datasheet it looks like the ground on the secondary side of the transformer is the isolated ground. Are all the other grounds tied together? In the attached image, are all grounds numbered 1 through 8 input grounds except for 8 which is the isolated ground?

Thanks for helping

  • 0
    TI__Genius 15855 points

    Hi Yetkin, 

    Thanks for using E2E. A SEPIC is not an isolated topology. If you need isolation, i would recommend to use LM5158 in flyback configuration. 

    There is also an application note about how to isolate a SEPIC: https://www.ti.com/lit/ta/ssztcx0/ssztcx0.pdf 

    Yetkin Serimer said:
    AGND and PGND pins — are those grounds tied together?

    These pins has to be tied together. Normally in one single point on the board below the IC. AGND is meant for having a more quiet GND for connecting the sensitive parts. But these GNDs can not be seperated. 

    The grounds in the schematic are AGND and PGND. All are tied together. The topology is not isolated. 

    Best regards

    Moritz