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LMR64010: Issue regarding thermal calculation

Chaithra HV
Prodigy 10 points
Part Number: LMR64010

Hi,

 

                We have used LMR64010XMF/NOPB for generating 27V and 80mA from 12V.

      Calculation for power dissipation of LMR64010XMF/NOPB is given below,

    •        Power dissipation calculation as per current consumption by load,

Input voltage VI = 12V

Output voltage VO = 27V

Output current  IO = 0.080A

PO = VO X IO = 27 X 0.080 = 2.16W.

PI = P0/Efficiency = 2.16/0.84 = 2.5714W  (Efficiency = 84% as per datasheet)

PD = PI – PO = 2.7 – 2.5714 = 0.411W

 

    •  Power dissipation calculation as per θJA 

θJA=265 Deg C/W, Tj = 125, Ta = 50 Deg C

PD = (125 – 50) / 265 = 0.283W

  

  As per θJA calculation, we are getting 0.28W, but as per power consumption of a load we have got 0.54W.

                   Kindly let us know, which one to be consider for thermal calculation.

  • 0
    TI__Intellectual 2655 points
    Hi Chaihra
    The first calculation: Power dissipation calculation as per current consumption by load,
    PD = PI – PO = 2.7 – 2.5714 = 0.411W
    It is the total loss, which is include inductor loss, diode loss, IC loss and others.

    The second calculation: Power dissipation calculation as per θJA
    PD = (125 – 50) / 265 = 0.283W
    it means the maximum IC loss that our device can hold according to θJA.
    θJA is a measure of the thermal performance of an IC package mounted on a specific test coupon, which is different from our application. So the thermal resistance in our board will be smaller than θJA.