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TL431 application

Nanfang Liao
Intellectual 2085 points
Other Parts Discussed in Thread: TL431

Hello All,

My customer is using our TL431. The Vz is 5.5V, the current is 55mA, the max PCB temp is 75C, please help to calculate what's the TJ temp? is there any risk of this application? thanks

Regards,

Nanfang

  • 0
    TI__Mastermind 24985 points
    Hello Nanfang,

    I have moved your post to the newly formed Voltage References forum.

    By Vz, do you mean the cathode voltage? If so, the power consumption for this device will be about 300mW. If we take a look at the ThetaJA value for this device, then the device would be expected to heat up at 206C/W * 300mW = 61.8C.
    61.8C + 75C = 136.8C.

    Is there a reason why they are biasing at 55mA?
    This seems like a lot, since much less current is required to bias the voltage reference.
    Best,
    Michael
  • 0 in reply to Michael J Schultis
    TI__Intellectual 2085 points
    Hello Michael,

    Thanks for your quick response. The 55mA is the load requirement. The customer also tested the Tc for different load current and calcuate the Tj as below. They want to know if our part run long time and no reliablity issue, what is the max load current do you suggest? thanks

    Load Tc thermal θjc Tj
    55mA 85.3 0.3025 76 108.29
    45mA 83.8 0.2475 76 102.61
    37mA 84.7 0.2035 76 100.166


    Regards,
    Nanfang
  • 0 in reply to Nanfang Liao
    TI__Mastermind 24985 points

    Hello Nanfang,

    This device is rated for 100mA, so operating at 55mA should be no problem, but I would recommend that the device junction be held below 125C. 

    Based on the measurement and calculation you provided, this should be acceptable for the device assuming the junction to case is the best indicator. In order to achieve better thermal performance, I would suggest thick copper traces to each of the pins and the anode to be either connected with a thick copper trace to ground or connected to the ground plane directly to aid in thermal dissipation.

    Best,
    Michael