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LMR36006-Q1: Switching Loss Calculation / Estimation

Christoph Breitweiser
Prodigy 20 points
Part Number: LMR36006-Q1

Hi,

i am trying to calculate/estimate and compare the power losses and especially the switching losses for the following parts:

  • LMR36006AQRNXRQ1
  • LMR36006BRNXR

As shown in Application Report SLVAEQ9 i need a couple values of the integrated MOSFETs not provided in the datasheet to calculate equations 3 - 6:

  • Qgs2
  • Vdr
  • Vpl
  • Vgs(th)
  • Rg
  • Rdrive

Are these values available or are there any other recommended ways to calculate / estimate the switching losses?

Regards and thanks in advance.

  • +1
    TI__Guru 57555 points

    Hello

    The internal FET parameters are proprietary and can not be given out.

    However, the best way to determine the total loss of the converter is to use the efficiency curves in the data sheet.

    Or, the TI Webench tool can be used to give the total power loss of the converter.  The total loss based on the efficiency is = Po*(1-n)/n

    Where Po is the output power and n is the efficiency.  You can subtract the loss in the inductor and get an estimate for the converter loss.

    If for some reason you need to separate out the switching loss, you can calculate the conduction losses and then subtract those from the total loss.

    The result would be an estimate of the switching loss for the converter and inductor.  The conduction losses are those produced in the Rdson of the FET(s)

    and the inductor resistance, and are calculated as shown in the app note you referenced.  

    Note the the total loss in the converter is the parameter you need when estimating the junction temperature of the device.

    I have attached an app note here that may be helpful.

    Thanks

    5282.snva951.pdf