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DAC3484: Case temperature calculate

Derek Xie
Genius 12255 points
Part Number: DAC3484

Hi Team:

Could you help me to check how to calcultae the case temperature when the junction temperature is 125 degree?

In the datasheet only have Theta JC, don't have power consumption and efficiency. Could you help me to check how to calculate it? Thanks.

  • 0
    TI__Intellectual 775 points

    You could use the following equation to back calculate the case temperature : 

    TJ = TC + (ΨJT * Power)

    You'll find that the case temperature is almost equal to the junction temperature for this device and will be around 124.8oC when it is operating under its max conditions. Feel free to read through the following app note: SPRA953C. It describes various thermal metrics and other useful information, including the equation mentioned above.

    Regards,

    Abdallah

  • 0 in reply to Abdallah Obidat
    TI__Genius 12255 points
    Hi Abdallah:
    I know the function, but how to calculate the power? The datasheet only show the power consumption, no effeicency and else.
  • 0 in reply to Derek Xie
    TI__Genius 12255 points

    Hi Abdallah:

    Customer test the DAC3484's power consumption is 1.2W. How to get the case temperature? 1.2 *Theta jc?

  • 0 in reply to Derek Xie
    TI__Intellectual 775 points

    Psi JC is listed in the datasheet as 0.1 or 0.2, depending on the device package. You would use the equation I listed in my previous post to calculate the case temperature. For your case, you would subtract the product of the device power and Psi JC from the junction temperature: 125 - (0.1*1.2) = 124.88 C. 

    I am unsure by what you mean regarding the DAC "efficiency". The DAC has a defined output that is not proportional to input power. The power consumption of the DAC changes as you turn on/off various digital blocks in the device. For example, using a NCO would require additional power consumption. It is more common to use a metric like efficiency for devices such as power converters (Buck, boost, etc...).

    Regards,

    Abdallah

  • 0 in reply to Derek Xie
    TI__Genius 12255 points

    Hi Abdallah:

    Thanks. One more question, if customer test the board is about 65 degree. How to verify the junction temperature?

  • 0 in reply to Derek Xie
    TI__Intellectual 775 points

    You can use the following equation to determine the junction temperature:

    TJ = TPCB + (ΨJB * Power)


    The value for Psi JB can be found in the datasheet. For your specific case, the junction temperature would be: 65+(4.6*1.2) = 70.52 oC if the device package is a QFN or 65+(4.6*1.2) = 70.52 oC. If the device package was a BGA, then the junction temperature would be: 65+(4.6*1.2) =  84.68 oC.

    You would need to take care when taking the measurement on the PCB. Please refer to the previously posted app note for more information.

    Regards,

    Abdallah