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TPS54531 - Package Dissipation Ratings

Hirotaka Matsumoto
Guru 27585 points
Other Parts Discussed in Thread: TPS54531

Hello,

We'd like to Package Dissipation Ratings of TPS54531.
On the data sheet, following values show.

1. Thermal impedance / Junction to ambient　：50℃/W
2. Pseudo thermal impedance / Junction to top：5℃/W

<Question>
Why is "Pseudo thermal impedance Junction to top" much lower compared with "Thermal impedance Junction to ambient"?
Does "Psuedo" mean that there is no thermal impedance Junciton to top on TPS54531(no thermal PAD on top)?

Please teach us about Psuedo thermal impedance Junction to top. 

Kind regards,

Hirtotaka Matusmoto

  • 0
    TI__Guru**** 191445 points

    TPS54531 is  recently released device.  I'm surprised it does not have a full set of thermal parameters.  But to answer your question, Pseudo Thermal Impedance is more correctly known as Psi JT or the junction to top characterization parameter.  For thermal pad packages, it is assumed that nearly all the heat is transfered out of the junction by way of the thermal pad.  The characterization parameter gives the difference it top of case temperature relative to the junction temperature in C/W assuming the thermal pad is well connected to a proper copper grounding area.  Psi JT is typically much lower than Theta JA.  See below for more details:

    http://www.ti.com/lit/an/spra953b/spra953b.pdf

  • 0 in reply to JohnTucker
    Guru 27585 points

    John san,

    Thank you for your prompt reply.
    We could recognize that Pseudo Thermal Impedance is Psi JT(Junction to Top of Package).

    Kind regards,

    Hirtotaka Matsumoto