Micrel
MIC2589/MIC2595
of the tFLT, and read up the Y-axis scale to find the
intersection of the Single Pulse curve. This point is
the normalized transient thermal impedance (Zθ(J-C)),
and the effective transient thermal impedance is the
product of Rθ(J-C) and the multiplier, 0.9 in this
example. Solving Equation 3,
Finally, add this result to the maximum steady state
junction temperature calculated previously to
determine the estimated maximum transient junction
temperature of the MOSFET: TJ(max.transient) =
74°C + 72.6°C = 146.6°C, which is safely under the
specified maximum junction temperature of 200°C for
the SUM110N10-09.
TJ(transient) = (201.6W) × (0.4°C/W) × 0.9 = 72.6°C
Figure 8. Transient Thermal Impedance – SUM110N10-09
24
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