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WEBENCH® Tools/LM73606: Correct Light Load Efficiency Value

RJ
Intellectual 2550 points

Part Number: LM73606

Tool/software: WEBENCH® Design Tools

Hello Team,

I am helping to support a question on the LM73606. Specifically we are trying to achieve 90% efficiency under light load. Figure 33 in the datasheet points to it being possible, but WEBENCH provides an "N/A" when trying to do it. I am looking for assistance with this as we are looking for verification.

Parameters: Vin=24, Vout = 6V, Iout = 20mA-200mA

Questions:

  1. Is there data or suggestions you can provide on an inductor for this application? (formula for inductance, DCR of inductor, and efficiency relation)
  2. Do you have the inductor PN that was used to provide the data captured in figure 33 of the datasheet?
    1. Would this be the same part number that is on the EVM: XAL7070-222MEB?


I greatly appreciate your assistance with this!

Regards,

Ramon

  • 0
    TI__Mastermind 25590 points

    Ramon,

    The inductance will depend on your switching frequency and typical load. As always, you can use WEBENCH or the EVM for a guideline on value of inductor. As for relation to efficiency, the inductor will have copper loss (due to DCR) and core loss (due to the material and construction of the inductor/core).

    • Core loss will be generally constant over output current
    • Core loss will scale with switching frequency. Higher switching frequency will get more core loss.
    • Copper loss will increase with I*I*R (output current)
    • Copper loss will stay relatively constant with changing switching frequency.

    Check the DCR of the inductor to calculate copper loss. You may also find info on core loss in the inductor datasheet.

    I'm looking for the exact inductor used in figure 33. I'll get back to you with a part number. In the meantime, you can use Wurth's Red Expert or Coilcraft's Power Inductor Finder to find a good inductor.

    -Sam

  • 0 in reply to Samuel Jaffe
    TI__Mastermind 25590 points
    Ramon,

    Yes, the efficiency curves on the datasheet are all taken on the EVM. So the EVM inductor is the same inductor. You can use that inductor or look for something that better fits your needs. The EVM is designed to optimize all-around performance but if your application can spare cost for efficiency, I'm sure there's a better suited inductor for you.

    -Sam