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TL4242 TJ Calculate

Hugo Liu
Genius 5095 points

Hi Sir,

We are want to application TL4242DR, But our Product board Tc measurement is 105C, Because i can't found the θjc in datasheet, Could you please help to calculate the TJ is under 150°C and θjc value?

Application condition Vout=24, Io=200mA, TC=25°C

Thanks, Hugo

 

  • 0
    Genius 5095 points

    Update Application condition. 

    Application condition VIN=24, Vout=19.8V, Io=200mA, 6 Series x7 parallelLED, TC=25°C

  • 0 in reply to Hugo Liu
    TI__Genius 14890 points

    Hugo,

    Two key components for this question are the power consumed and the thermal dissipation from the IC to the board / air.

    For your application, the power consumed by the device would be (24V-19.8V) * 0.2A = 0.84W.  This will vary with current and the forward voltage of the LEDs.  

    The thermal dissipation will vary based on a number of factors.  The main factor is the PowerPAD to PCB connection.  The datasheet shows JESD 51-5 and 51-7.  These vary considerably based on the methods used.  

    In the case discussed here, the θjc and the θja will be similar.  Using the θja of JESD 51-5 of 49.5C, the calculated junction temperature would be approximately (49.5C/W * 0.84W) 42C above the ambient (case for this discussion) or 105C + 42C = 147C.  Each application will yield different results based on the true dissipation.

    Regards,

    Dick