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TPS54427: measurement condition of Theta_JA & VFBTH at the 5~50 degree C

Part Number: TPS54427

Hi team 

1. Could you share the measurement condition of Theta_JA for TPS54427DDA? Customer is wondering 42.1℃/W can be used at their condition, that is the 4 layer board.

2. How do they estimate the value of VFBTH  at the 5~50 degree C, though  VFBTH  is specified at -40 to 85C at the datasheet?

Regards,

Noriyuki Takahashi

  • hi Takahashi,

    1. The measurement condition of Theta_JA, please refer file in below link:
    (www.ti.com/.../spra953c.pdf)

    also, please use WEBENCH DESIGNER to estimate the thermal.

    2. datasheet page 7 figure 9 can help you to estimate VFBTH value.

  • Takahashi-san,

    The thermal parameters use a JEDEC standard coupon.  If memory serves, it is 4" x 4.5 pcb.  It is really for direct comparison of relative thermal performance among many different devices under the same PCB conditions,  Your actual application performance may vary considerably.  There are two main factors to onsider:

    1.  Your application PCB may be designed fro better thermal performance with thermal vias, internal planes, etc.  These may improve thermal performance.

    2.  In the test coupons, only the power dissipated in the IC is considered as the load is external.  In real life applications, th eTPS54427 may be used as a point of load regulator with the load closely located on the PCB.  TPS54427 may operate at near 90% efficiency.  So 90% of the power will be dissipated at the nearby load and only 10% dissipated by the IC.  In the thermal model test case, only this 10% is dissipated on the test coupon.  In an actual application, this 0ther 90% may be dissipated nearby adding to the PCB heating and elevating the TPS54427 junction tempurature,

    The IC characterization ais done at only a few temperatures.  5 C. and 50 C are not specifically tested.  Figure 9 in the datasheet is your best estimator of performance.

  • John

    1.  Your application PCB may be designed fro better thermal performance with thermal vias, internal planes, etc.  These may improve thermal performance.

    -->In order to make sure the PCB is designed with better thermal performance, they would like to confirm the PCB information to get theta_JA. It seems that there are several JEDEC standards like JESD51-1, 2, 3...  I think TI devices also follow on one of these standards. So could you specify which standard TPS54427 follow on?

    2. The IC characterization ais done at only a few temperatures.  5 C. and 50 C are not specifically tested.  Figure 9 in the datasheet is your best estimator of performance.

    --> I understood that there are no data in the temperatures. Can you mention anything about how to estimate the trend of min&max value of the VFB threshold voltage when the temperature range is reduced? It is OK that this is not guaranteed. Customer just wants to know the trend, in general.

    Regards,

    Noriyuki Takahashi

  • Takahashi-san,

    I researched this some time ago.  I do not recall which standard, but it is the 4.5" x 4" JEDEC pcb.  Beyond that any information would be in the above referenced app note.  I will reach out to the modeling team to see if they have other info.  It generally take a while for them to respond.

    I can review the char data tomorrow to see if I can discern any trend on FB voltage vs temperature.

  • Hi John,

    This is just a kind reminder.

    Could you get any update?

    Regards,

    Noriyuki Takahashi

  • Takahashi-san,

    There is no further information available.  Sorry.

  • Please let me know if you get any information.

    Customer wants those information on the early next week.

    Regards,

    Noriyuki Takahashi

  • Takahashi-san,

    There is no further info available.