• State
  • Locked Locked
  • Replies 1 reply
  • Subscribers 62 subscribers
  • Views 953 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LM3478: Power supply won't start - looking for guidance to debug

Bruno Saraiva
Guru 13040 points
Part Number: LM3478

Fellows,

We have several successful implementations of power supplies within our projects, mostly based on Webench. This particular one, however, has been causing me to pull some hair off...

If we enable VIN, current peaks up as high as we allow it to (as if there is something shortened on the circuit below it), and the power supply won't start.

We've looked for the most common causes and for shorts as well, finding none. There are three similar boards, same status. We thought maybe this IC needed some initial load to crank up, added a load to draw ~100mA from it before starting, but no good.

I'd appreciate if someone can take a look at the circuit for maybe an obvious mistake, or guide on how to further diagnose this.

Thanks a lot, regards.

Bruno

  • 0
    TI__Expert 4100 points

    Hi Bruno,

    Your schematic looks Ok, nothing obviously wrong.

    From the problem description you provided above it appears that there is either a short circuit or large inrush current causing power supply to rail.

    To handle potential issues with inrush current

    1. would suggest adding capacitor between G&D of Q11. I would start with 100nF and than check if you see any difference in behavior. Increasing this capacitance should decrease inrush current and vice versa.
    2. Also make sure that switching FET you are using is correctly dimensioned. Quick check with webench, came up with 80V/23A device (BSC340N08N)

    Best regards

    Brani