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About figure 1,2,3 in the TL783 datasheet.

toshiya nasu
Prodigy 30 points
Other Parts Discussed in Thread: TL783

Hello!

I have four questions about TL783 datasheet.

About figure 1 and 2.

  1.What meaning is "TW"?

  2.Why is "Tj" constant?
     Do not device heat?

  3.Why has "Output Current Limit" decreased?
     Though "VI-VO" is increased.

About figure 3.

  4.Why has "Output Current Limit" decreased?
     Though "Tj" is constant.


Could you please teach me?
Thanks.

nasu.

  • 0
    TI__Expert 8890 points

     

    Hello Nasu,

    The current limit for this part varies with time.  The current limit also varies as a function of the hottest semiconductor junction temperature, Tj.  Of course the hottest semiconductor junction temperature is a function of the ambient temperature and the power dissipated across the part (Tj = Ta + Pd*Theta_ja,  where Theta_ja is the thermal resistance (degC/Watt) betweeen the junction and the ambient air)

    Figure 2 shows the current limit measurement for the case for various junction temperatures versus the input-output voltage dropped across the part measured at 1ms after current limit is reached.  Figure 2 shows the same information measured 30ms after current limit.

    Regards

    Bill 

  • 0 in reply to Bill Stokes
    Prodigy 30 points

    Hello! Bill,

    Thank you for your quick reply.
    I have a additional question.

    I expected that "Thermal-Shutdown Protection" decreases "Output Current Limit" in figure 3.
    However, Tj=25degC (constant) in the figure.
    Is my idea incorrect?

    Could you please teach me?


    Best Regards.

    nasu

  • 0 in reply to toshiya nasu
    TI__Guru**** 164426 points

    Hello Nasu,

    In figure 3, Tj is only 25C when time = 0mS. During the 30mS test Tj will rise as expected.

    Regards,
    Ron M.

     

  • 0 in reply to Ron Michallick
    Prodigy 30 points

    Hello Ron,

    Thanks for your explanation.

    Regards,
    Nasu.