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LMR51430: Tj calculation result

JH Shin
Guru 11480 points
Part Number: LMR51430


Hello,

My customer reviews to use LMR51430 under the following conditions.

  - VIN = 10V~30V, VOUT = 9V, IOUT = 2A

They calculated the expected Tj for the worst-case temperature with the formula below.

   

      Ta = 85℃, RθJA = 107.8℃/W,  Power = 9V*2A = 18W

In this case, this device cannot be used because it exceeds the allowable Tj specification.

1. Is the Tj calculation above correct? What is the maximum ambient temperature allowed for 9V@2A with this device?

2. Can you please recommend a DC/DC converter product that can be used at a higher ambient temperature for the customer's VIN, VOUT and IOUT?

Thank you.

JH

  • 0
    TI__Mastermind 27470 points

    HI 

    power is not output put , it is power loss , for 18W with 94% efficiency, the loss is 1.15W

    107.8deg C/W is based on JDEC standard, in 4 layer PCB with proper copper, the theta theta JA will be around 60deg C/W. The temperature raise will be around  60deg C

    Thanks