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TPS54528 / Question about Psi-jt

S.Satoshi
Guru 21685 points
Other Parts Discussed in Thread: TPS54528

Hi Everyone,

Please let me ask about Psi-jt of TPS54528.

  1. Please let me know the test environment when Psi-jt was measured. Specifically our customer is asking the airflow condition and PCB used at testing. Was it no airflow and EVM used?
  2. Please let me know how to estimate Psi-jt under airflow condition. If the Psi-jt listed in datasheet was measured with no airflow, our customer want to estimate Psi-jt under airflow condition. Now I'm referring app report SPRA953B and find attached table. In the case of 1s PCB, the Psi-jt at 250 LFM rises 2.6 times compared with at 0 LFM. Then does it rise 5.2 times at 500 LFM? And can we apply this value for TPS54528. I understand that it's difficult to provide exact value, so please give your advice to estimate it roughly based on your experience.

Your advice will be appreciated.

Best Regards,

Sonoki / Japan Disty

  • 0
    TI__Guru**** 191445 points
    The Psi-JT value is a calculated value from a JEDEC standard model, not measured. I will have to research the airflow characteristic. I expect it will be exponential or square law, not linear.
  • 0 in reply to JohnTucker
    TI__Guru**** 191445 points
    Actually:

    From the packaging team:

    "Airflow is not something we test for regularly and fan location, direction and airspeed will all impact how the device cools so it will be very difficult to align with what they are doing in the labs. If the package type is similar for the device in the app note, then the approximation they suggest is probably a fair approximation without really delving into the exact setup."

    So Psi JT is increased by a factor of 2.6x or 2.8x for 0 vs 250 LFM. For a rough approximation can you expect it to multiply by the same factor for 500 LFM ( Psi JT = 4,6 and 3.9 C/W respectively).

    If you need greater accuracy than that you would probably need to model your explicit system using the appropriate software. Let me know if you have further question