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LM2743 Junction Temperature @ Ambient Temperature of 85 deg C

Anand Kumar Rai
Intellectual 720 points
Other Parts Discussed in Thread: LM2743

Hi folks,

I am using LM2743 in one of the power supply applications, I want to know the junction temperature of the IC at ambient temperature of 85 deg C. After simulating using WEBENCH it show the junction temperature(Tj) to be 45 deg C at the ambient temperature of 30 deg C. Since WEBECH is not allowing to change the ambient temperature to 85 deg C. I tried to calculate using the data given in datasheet, but its coming around 2000 deg C which looks incorrect in any case. I am using the following formula for calculation:

TJ = TA + (RΘJA * PD)

But it looks RΘJA specifications are not clearly given in the datasheet. I took it as 155 deg C/W.

My input is 5.0V and output is 1.1V @ 15 Amperes.

Thanks in advance for your support.

Thanks and Regards

-Anand Kr. Rai

 

  • 0
    TI__Expert 3545 points

    Anand,

    The  RΘJA is the thermal resistance from junction to ambient.  When you mount the LM2743 to a PWB what you need to know is the  RΘJB, the thermal resistance from the junction to the PWB, this is normally much lower than  RΘJA.

    I went into WEBENCH and I was able to change the Ta to 85C, I'm not usre why you were not.  I have attached the secreen shot Tj is 96.5C

    Terry

     

  • 0 in reply to Terry Allinder
    Intellectual 720 points

    Hi Terry,

    Thank you very much for your quick support. This is for what I love TI.

    Actually I selected LM2743 from the list of solutions when I entered my input and output requirements in WEBENCH, and I got the schematic to be used, I was expecting that I can the temperature only if there is Thermal Analysis option available with the chip. But I did not know where is that option.

    Anyways my problem is solved. Thank you.

    Best Regards

    -Anand Kr. Rai