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TS3A44159: Calculating Maximum Junction Temperature and Understanding RJA and RJC with Different Packages

Part Number: TS3A44159
Other Parts Discussed in Thread: TPS736

1. what's the range of Junction temperature? min value and max value?

2. normally, RJA is larger than RJC, but in TS3A44159 datasheet, for RGT package, why its RJA is smaller than RJC?

thanks.

  • Hello Max,

    As far as the question for the difference between RJA and RJC for the RGT package, it is heavily dependent on the package as specified in this appnote:

    This document also has an equation for calculating the maximum Junction temperature, but here is another E2E link which helps explain it as well:

    Of course the numbers wouldn't be the same, but you could apply the same methods. You would apply the number which apply most to your application based on the snippet I have attached below:

    Thank you,

    Louie

    If I have answered your questions, please hit the Verify Answer button.

  • Hi Louie

    I don't want to calculate the TJ. I just want to know the Tj limitation.

    such as TPS736 datasheet,

    what's the value of TS3A44159?

    thanks.

  • Hello Max,

    As mentioned above, the Maximum Junction temperature can be calculated based upon the limitations I placed in the snippet above.
    From the snippets above you know that the Tja constant is 45.4 C/W. We also know from above that the maximum continuous current from the switch is 200mA, while the peak maximum(at limited pulses) is about 400mA. The maximum continuous Icc allowed is 100mA and the Vcc, which is also the allowed limit on the switch is 4.6V. With these numbers you can calculate the maximum TJ:
    TJ = Ta Max+ Tja(Max Power through switch + MaxPower through Vcc)
    TJ = (85 C) + 45.4C/W (4.6V* 0.1A + 0.2A*0.2A*0.3)
    TJ = 85C + 45.4C/W(0.46W + 0.012W)
    TJmax= 107C

    If you look closely at the absolute ratings snippet above, you can note that the calculated TJ is much lower than the storage temperature, therefore you will not damage your device running it at this temperature. We would not recommend running this device past the temperature we have calculated for risk of damage to the device or unknown performance.

    Thank you,
    Louie