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LM2937: Comparsion SOT-223 package LM2937 and LM2940 power dissipation

Jan Bock
Intellectual 2650 points
Part Number: LM2937

Hi Team,

By re-reading the datasheet, we have a doubt concerning temperature.

  • In LM2937, we can see this curve :

  • In lm2940, this one :

So my interpretation is that at 85°C ambient temperature(with the same package), LM2940 can dissipate 0.5W & LM2937 can dissipate 0W.

From my understanding the LM2940 the should have the same graph if you use the formula pmax=(Tj-Ta)/R_thetta_Tj. Is the graph for LM2940

correct though?

Thanks 

Jan

  • 0
    TI__Expert 5251 points

    Hey Jan, 

    We discussed over email already, but can look into this more please allow 2-3 business days. 

    Thanks, 

    McKyla

  • 0 in reply to McKyla Beuttler
    TI__Expert 5251 points

    Hey Jan, 

    No, these graphs look correct. Yes, Tjunction temperature = (Power dissipation * R thetaJA ) + TA   

    The LM2940 and LM2937 do have similar R thetaJA, hence why the slopes are similar, but because these are different devices they handle increases in power dissipation different and the temperatures are going to be different. 

    Keep in mind that these graphs are also scaled differently as well, and to the JEDEC standard. If the LM2940 device is going to operate close to 85°C we would recommend a different device and package as it will not be able to handle any power dissipation. Additionally, if the customer is still wanting to use this device since this is tested with the JEDEC board there is about 30-50% improvement on thermals that can be made with optimal board layout. link to app note

    I hope this helps! Let me know if you have any further questions. 

    Thanks, 

    McKyla