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CSD87381P: Regarding thermal failing for 1.8V at 1A, Junction temperature excedded.

Gayathri Palla
Prodigy 70 points
Part Number: CSD87381P

Tool/software:

Hi Team, 


I am theoretically calculating the thermal performance for the CSD87381P at 1.8V/1A, and it is reaching 151.56°C  falling. The thermal resistance (RθJAR_{\theta JA}RθJA​) considered is 84°C/W, and the junction temperature is set at 125°C. Please clarify how to properly account for thermal calculations

Thanks,

Gayathri. 

  • 0
    TI__Mastermind 38320 points

    Hello Garathri,

    Thanks for your interest in TI FETs. Let me make sure I understand your question and conditions. First, what is the application? Is the CSD87381P being used in a synchronous buck converter with 1.8V at 1A at the output? Or, are you assuming a 1.8V drop across the device at 1A (1.8W)? The maximum power dissipation capability of this package is about 1.8W on a multilayer PCB with a good thermal layout. Of course, is is dependent on your ambient conditions. Rθja is specified in the datasheet on a single layer PCB with 2oz, 1in² copper pad which probably is not representative of your PCB. The actual Rθja in your system is probably lower depending on the board stackup and design. Please see technical article at the link below on how TI tests and spec thermal resistance in our FET datasheets. The main path to remove heat for the CSD87381P is thru the pads soldered to the board and into the PCB. Because of the metal tab, this device can also be used with a heat sink. I pulled up the applications data for the CSD87381P collected during product development. In a sync buck operating at 12Vin to 1.3Vout at 500kHz switching and 0.95μH inductor. The measured power loss at 15A was about 3.3W and the temperature of the device was 78°C with no airflow. The equates to an equivalent Rθja of about 16.2°C/W. The measurements were made on a PCB design with dimensions of 4 inches (W) × 3.5 inches (L) × 0.062 inch (H) and 6 copper layers of 1 oz. copper thickness as shown in the datasheet. Please let me know if you have any questions.

    https://www.ti.com/lit/pdf/SSZTB80

    Best Regards,

    John Wallace

    TI FET Applications

  • 0 in reply to John Wallace1
    TI__Mastermind 38320 points

    Hi Garyathri,

    Apologies, I misspelled your name.

    Thanks,

    John

  • 0 in reply to John Wallace1
    Prodigy 70 points

    Hi John,

    We are using this Mosftet along with PMIC TPS6508641RSKT  to power the Zync ultrascale plus. Our query is w.r.t the 1.8V rail where the current consumption is 5A. We want to know. Power consumption this Mosfet at 5Amperes.As per our calculation using the power calculator for this device its is around 1.139Wwatts. Please let us know.

    Based on the above we will recalculate the junction temperature and check if its within the maximum ratings as per datasheet.

    Thanks,

    Gayathri.

  • 0 in reply to Gayathri Palla
    TI__Mastermind 38320 points

    Hi Gayathri,

    Thanks for the update. Power dissipation of 1.139W is within the capabilities of the package. Please follow the layout recommendations in the datasheet to get the best thermal performance. TI tested on the PCB described in the datasheet and referred to in my earlier response. The effective Rθja for that board was about 16°C/W. You can work this backwards to determine a target Rθja value for your conditions: Tj= Tamb + Rθja x Pd -> Rθja = (Tj - Tamb) / Pd. For example, if Tamb = 55°C, Tj = 125°C, then Rθja = (125°C - 55°C) / 1.139W = 61.5°C/W. You should be able to achieve this by following the layout recommendations in the datasheet.

    Thanks,

    John