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LM4050QML: Transient Reverse Current Rating / Power Dissipation

Stewart Laird
Prodigy 30 points
Other Parts Discussed in Thread: LM4050-N-Q1

The LM4050QML has an Absolute Maximum Reverse Current rating of 20mA, but determining a maximum power dissipation at, for example, ambient=60C yields


Tjmax=+125C


Ta=+60C


Thermal Resistance Tr=214 C/W


PDmax=(Tjmax - Ta)/Tr=303mW


For a 5V reference, PDmax=V*Imax, Imax=303mW/5.0V=60mA (3x larger than the rated absolute maximum reverse current)


Wondering if there is a different limiting factor besides junction temperature that is resulting in the 20mA rated absolute max? Or whether the junction temperature calculations can be used to determine a more refined/application-specific absolute maximum reverse current rating?


I am interested in the effect of current transients (<10ms) that exceed the 20mA level and whether they truly represent an overstress condition.

  • 0
    TI__Intellectual 1745 points

    Steward,

    I do not have details about the reason for the 20mA rating, but the two ratings (max current and max junction temperature) are independent ratings.  The system should be designed to stay within all maximum ratings.  The effect of transients greater than 20mA has not been tested, but the peak value, time (you mention 10ms) and frequency of the events would be the factors that could affect performance or lifetime.   

    If this is a key concern I suggest testing a few units in the lab under the conditions you expect to see in your application.

    As a side note, I see the Thermal resistance in the datasheet for LM4050 is 287 C/W, not 214 C/W.  

    Chris

  • 0 in reply to Christopher Dean
    TI__Intellectual 1745 points

    Hi Steward,

    I was mistakenly looking at the LM4050-N-Q1, not the LM4050QML.  The thermal resistance you mentioned is correct.    The rest of my comments do remain the same however.

    Chris