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TPS54620: how to calculate the power dissipation of the device?

Howard Zou
Genius 12365 points
Part Number: TPS54620

Hi,

there is an app note that tells us how to calculate efficiency and it's written based on TPS54620

http://www.ti.com/lit/an/slva390a/slva390a.pdf

On page 5 equation (16), P=Io*Io*Rdcr=4A*4A*0.104ohm=166.4mW which is wrong, it should be 1.664W.

If it's 1.664W, then equation (17) other losses would be negative.

So I would like to know where is wrong?

Further more, I ask this question because my customer would like to calculate the junction temperature

By using Tj= Ttop+ ψJT*(power dissipation on device).

Then we need to calculate the power dissipation on device.

But how can we calculate that? Is it (Pfet+other losses) described in the app note above SLVA390A?

  • 0
    TI__Guru**** 191445 points

    Howard,

    The mistake is in the inductor DCR.  It should be 10.4 mohm, not 0.104 ohm.

  • 0
    TI__Mastermind 35115 points

    Hi Howard,

    Is the customer trying to estimate the junction temperature based on some ambient temperature condition or is the customer trying to calculate the junction temperature based on a measurement?

    The Psi JT number is used for estimating the junction temperature based on a measurement of the temperature at the top of the IC package. As this is a measurement, the customer could measure the efficiency or power loss at the same time the temperature is measured. The DC and AC power loss in the inductor should be subtracted from the total power loss. Additionally, as Psi JT number is generally very small, the junction temperature is very close to the temperature at the top of the IC package.

  • 0 in reply to Anthony F
    TI__Genius 14455 points

    Hi Howard,

        Just trying to follow up on Anthony's question.

    Regards,

    Gerold