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LM1084: Over Heat for LM1084

MAHALAKSHMI M
Prodigy 10 points
Part Number: LM1084

Hi,

We have used LM1084IS-ADJ/NOPB for 24V TO 5V Conversion. we have faced below issue for PCB.

1. Heat Reached up to- 80 Degree. We have used only Less than .5A

That Time IC was Not working properly. Some Time IC was Burned and Input capacitance also Burned.

 

 

  • 0
    TI__Mastermind 18466 points

    Hello,

    With a Theta -JA of 40.4c/W

    PD = 9.5W @ 500mA 

    TJ ~ TA + 383.8 C which is fully out of the specs of this device. You are entering thermal shutdown.

    Best,

    Juliette

  • 0
    Prodigy 10 points

    Hi Juliette,

    Thanks for your support. I did not get your point. Kindly explain once again.

    Regards,

    M. Maha

  • 0 in reply to MAHALAKSHMI M
    TI__Mastermind 18466 points

    Hello M. Maha, 

    Because your part is burning, we would have to consider the Power Dissipation across the device. 

    PD = (VIN-VOUT)(IOUT)

    PD = (24V-5V)(0.5A)

    PD = 9.5W. 

    9.5W are being dissipated across the device. 

    If the junction temperature of the device goes over 150C, you risk damage to the device. You approximate your junction temperature by multiplying your PD by your Theta-JA value. 

    In this case, your Theta-JA is 40.4C/W

    Meaning that for every watt dissipated across the device, the junction rises 40.4C in relation to your ambient temperature

    TJ ~ TA + (Theta-JA)(PD)

    TJ ~ TA + (40.4C/W)(9.5W)

    TJ ~ TA + 383.8C

    With good board layout design, you can lower the Theta-JA up to 50%

    In this best case scenario:

    TJ ~ TA + 20.2C/W(9.5W)

    TJ ~ TA + 191.9C

    This is still above the ABS MAX rating of the device. These conditions cannot be supported by the device. 

    Best,

    Juliette