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WEBENCH® Tools/TPS54340: IC Pd value and ThetaJA value

K. Sasaki14
Guru 10200 points
Part Number: TPS54340

Tool/software: WEBENCH® Design Tools

Please let me ask about TPS54340 IC pd and ThetaJA value on WEBENCH.

Using condition is the following,
Vin: 32V to 40V
Vout: 24V
Iout: 3.3A
Ta: 56 degC (Actually we would like to set 60 degC, however we set 56 degC because IC Tj is over 150 degC at 60 degC setting.)

As a result, IC Pd was 3.6W and ThetaJA was 26 degC/W at 40Vin.

According to TPS54340 datasheet Power Dissipation calculation, I think IC Pd is 1.354W at 92 mohm Rds condition and 1.994W at 190 mohm Rds condition.
Why is there difference between WEBENCH IC Pd value and datasheet calculation value? Which is more accurate value?

Datasheet ThetaJA value is 42 degC/W. Why is WEBENCH value 26 degC/W?
How do you get WEBENCH value?


Finally, do you think we can use TPS54340 with this using condition?

Best Regards,
Kohei Sasaki

  • 0
    TI__Intellectual 2510 points

    Dear Sasaki-san,

    The rdson used in the TPS54340 model also accounts for temperature co-efficient.

    The other model parameters are tweaked to better fit the measured data. So, you can expect some differences between the datasheet’s simple calculations and WEBENCH’s more sophisticated model.

    The ThetaJA value of 26degC/W used in the model is good for the TPS54340 EVM board. ThetaJA is dependent on number of layers, thickness, etc.

    Best Regards,

    Flora