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How could I calculator thermal junction for TPS54426?

TH Liu
Prodigy 30 points
Other Parts Discussed in Thread: TPS54426

How could I caculator thermal junction temperature for TPS54426.pdf

Test condition:

1. Measure the thermal couple under surface temperature, Tc is 58.1°C

2. TPS54426 the = 51.3(°C/W)

3. =0.85 Watt.

4. This package have the Thermal pad. (We have to mount a PCB).

5. Not include Thermal pad condition =101.7°C

 

Question:

How could I evaluation of? (Need consider the Thermal pad condition)

Q1.How to use this formula (=*+) to calculate?

(Need consider Thermal pad containing proportional relationship both with Tc.)

Q2.Why the  >  from the TPS54426 specification?

( formula =+, normally the  > )

Test condition:

1. Measure the thermal couple under surface temperature, Tc is 58.1°C

2. TPS54426 the = 51.3(°C/W)

3. =0.85 Watt.

4. This package have the Thermal pad. (We have to mount a PCB).

5. Not include Thermal pad condition Tj=101.7°C

 

Question:

How could I evaluation of ? (Need consider the Thermal pad condition)

Q1.How to use this formula (=*+) to calculate ? (Need consider Thermal pad containing proportional relationship both with Tc.)

Q2.Why the  >  from the TPS54426 specification? (formula =+, normally the  >  )

Test condition:

1. Measure the thermal couple under surface temperature, Tc is 58.1°C

2. TPS54426 the = 51.3(°C/W)

3. =0.85 Watt.

4. This package have the Thermal pad. (We have to mount a PCB).

5. Not include Thermal pad condition Tj=101.7°C

 

Question:

How could I evaluation of ? (Need consider the Thermal pad condition)

Q1.How to use this formula (=*+) to calculate ? (Need consider Thermal pad containing proportional relationship both with Tc.)

Q2.Why the  >  from the TPS54426 specification? (formula =+, normally the  >  )

1.

  • 0
    TI__Prodigy 575 points

    Hi, TH,

    first is Theta_JA, and calculaiton for junction temp. is,

    Tj = Ta + Theta_JA * Pdiss, where Tj is junction temp. Ta is ambient temperature, Pdiss is power loss;

    but more accurate way is,

    Tj = Psi_jt x Pdiss + Tcase, where Tcase is the top temperature of the device.

    Note that the parameters are different under the circumstances where there's thermal PAD or not. 

  • 0 in reply to Nick Chen
    Prodigy 30 points
    Hi Nick:
    thank a lot response.
    but refer the spra953a.pdf at chap2(theta_jc) from TI.
    (Application Report SPRA953A,
    or SPRA953B, refer : www.ti.com/.../spra953b.pdf)
    Please details the proper method to determine the component junction temperature by measuring the case temperature for TPS54426.
    thank your very much.