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LM3150 (or any COT switcher) and Conducted Emission paper AN-2162

Jeremy Curtis
Prodigy 75 points
Other Parts Discussed in Thread: LMZ13608, LM3150

I am working on a design using an LM3150 to take 10v-30v and produce 5.25v out at anything between 0.5A to 5A depending on user needs.  Essentially using Webench to do most of the hard work in terms of the base design.  I was using an LMZ13608 but the cost of the module and soldering issues (I don't have a suitable oven to bake the parts which often arrive needing to be baked) have led me to look at an alternatives and the LM3150 looks to fit the bill.

Filtering is required, and looking at the AN-2162 paper and associated spreadsheet, I can plug in the figures to get details of the filter required?

I am assuming that Cin values are those generated by Webench on the LM3150 design, but is the switching frequency given in the Webench report valid given the off-time in the COT design could be variable?  Might seem a basic question but I just wanted to check.

  • 0
    TI__Genius 16025 points
    By using any COT architecture, the frequency will indeed dither however, the architecture will do it's best to keep it within the specified range. For example, a 500kHz part might see 450k to 550k. This should not compromise the design of your filter. However it is generally preferred to not use COT architecture for EMI sensitive applications.
  • 0 in reply to Anston Lobo
    Prodigy 75 points
    Thanks for this, whilst COT might not be ideal but the overall design looks like it will fit into the space I have available. It's all going into a extruded aluminium enclosure eventually which will help with the EMI side too.