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CSD87351ZQ5D: What is the junction temperature with ambient of 85degC?

Part Number: CSD87351ZQ5D
Other Parts Discussed in Thread: TPS53119,


The customer will be using TPS53119 and CSD87351ZQ5D for 12Vin to 5Vout/10A. Webench simulation result shows that the power dissipation for CSD87351ZQ5D is 1.21W with ambient temperature of 85degC.

May I know what is the junction temperature for CSD87351ZQ5D?

If we use Tj = Ta + Pd*Rthja = 85 + 62*1.21 = 160 degC. This exceed the junction temperature of 125degC.

Any concern to use this device for 12Vin to 5Vout/10A?


Gim Song

  • Hi Gim,

    Thanks for the inquiry. I had typed out a response earlier today but I guess I did not submit it. The thermal impedances specified in the datasheet are determined by testing on a standard PCB and may not reflect the customer's application. I cannot tell you the junction temperature. The thermal performance and effective RthetaJA in the customer's application is highly dependent on the PCB design and stack-up of the customer's board. The datasheet provides power loss data and normalizing factors with the power block operating in a synchronous buck converter. This information can be used to calculate the actual power loss and determine SOA in the customer's application. Please refer to the application information section of the datasheet. If you need help with the calculations, please email me at my email address.

    It is possible to achieve effective thermal impedance much less (<20C/W) than 62C/W specified in the power block datasheet with proper PCB design and stackup. You can see the recommended PCB layout in the datasheet.

    Please refer to the blogs below for more information.

  • Looks like I repeated the same blog twice. Try the one below instead. Dissipated 1.21W in this package should be OK with proper PCB design.

  • Hi John,

    Appreciate your response and sharing these technical notes as reference. Will work with customer on their PCB layout to improve thermal dissipation.


    Gim Song