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REF3440: DBV package thermal resistance PCN question

cafain
Mastermind 6365 points
Part Number: REF3440
Other Parts Discussed in Thread: REF34-Q1

Hi staff

DBV package thermal resistance PCN question

The customer was listed in the Before Revision F data sheet
Designed with thermal resistance.
RΘJB = 29.6 ℃/W, ψJB = 29.1 ℃/W　（ex: Revision B)
Recently, Revision F has changed the thermal resistance value of the DBV package.

Was this value a mistake from the beginning and was it fixed for the first time in Revision F?

The REF3440 data sheet (SBAS804F) page2 4 Revision History contains the following changes.
Notification Number: 20210611001

・Changed Thermal Information parameters to correctly reflect DBV package.

The thermal resistance value of the data sheet before Revision E is different.
Is the thermal resistance value written in Revision E a mistake? (Before Revision F)
RΘJB = 29.6 ℃/W, ψJB = 29.1 ℃/W

Since there is no PCN for DBV package,are the Thermal parameters of
REF3440 DBV RΘJB = 42 ℃/W, ψJB = 41.9 ℃/W from the beginning of Revision A?

I look forward to your information.
best regards
cafain

  • 0
    TI__Intellectual 1695 points

    I believe the numbers were aligned to the automotive variant. Need to check the reason for the change; will report again once confirmed.

  • 0 in reply to Ajay Padgaonkar
    Mastermind 6365 points

    Thank you for your support.

    Is the time to match the thermal resistance value of REF34-Q1 from REF3440 Revision F?
    Please tell me the thermal resistance value before that.

    In other words,
    Which of the following thermal resistance values 1 or 2 was shipped for Revisions A to E listed in the REF3440 data sheet?

    I think that it is shipped from Revision F with the thermal resistance value indicated by 2.

    1: RΘJB = 29.6 ℃/W, ψJB = 29.1 ℃/W
    2: RΘJB = 42 ℃/W, ψJB = 41.9 ℃/W

    best regards
    cafain

  • +1 in reply to cafain
    TI__Intellectual 1735 points

    Hi cafain,

    The physical package has not changed since the release, therefore it was always the values we have now in rev. F datasheet. That would be option #2 that you provided above.

    If your system has been working fine previously, then nothing will change in terms of your system performance.

    If this is for a new design, this may or may not be a problem depending on how the thermals were calculated. If you previously used RΘJB or ψJB, then the new numbers will make it apparent that you had less design margin this whole time. If you used RΘJA, then you will have gained margin (that you didn't know you had).

    As an aside, use RΘJB or ψJB for your designs. RΘJA is antiquated and assumes most of the heat is dissipated through the package, which is a bad assumption - most heat dissipates through the copper connections on the PCB to the part.

    See https://www.ti.com/lit/an/spra953c/spra953c.pdf for details on thermals.

    -Tony