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The information presented in this cross reference is based on TOSHIBA's selection criteria and should be treated as a suggestion only. Please carefully review the latest versions of all relevant information on the TOSHIBA products, including without limitation data sheets and validate all operating parameters of the TOSHIBA products to ensure that the suggested TOSHIBA products are truly compatible with your design and application.
Please note that this cross reference is based on TOSHIBA's estimate of compatibility with other manufacturers' products, based on other manufacturers' published data, at the time the data was collected.
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How to calculate for selecting a heat sink of a semiconductor device (2)

A calculation example is shown with the following products.

Target temperature is less than 90 deg.C in consideration of reliability.

Product: TTD1409B
Ambient temperature: 60 [deg.C]
Heat sink: No use
Power dissipation: 1 [W]
Rth(j-a): 62.5 [deg.C/W] refer to datasheet (= (150 – 25 ) [deg.C] / 2 [W])
Rth(j-c): 5 [deg.C/W] refer to datasheet = (150 – 25 ) [deg.C] / 25 [W])
(Absolute maximum rating Tj(max) = 150 [deg.C], PC= 2 [W] at Ta = 25 [deg.C], PC= 25 [W] at Tc = 25 [deg.C])
This situation: Tj = 122.5 [deg.C](= 62.5 [deg.C/W] × 1 [W] + 60 [deg.C])

When the contact resistance between a semiconductor device and a heat sink is disregarded, “Thermal resistance, Junction to Case Rth(j-c)” and “Thermal resistance, Junction to heat sink Rth(j-cf)” are considered to be the same.
Rth(cf-a) = (( 90 – 60 ) / 1 ) – 5 [ deg.C / W ] = 25 [ deg.C / W ]
To use the heat sink with a thermal resistance value lower than 25 deg.C / W, you can obtain the result to be expected.

When using the above-mentioned technical content such as product data, figures, and tables, please judge whether the application is appropriate at your own responsibility based on sufficient evaluation of the product alone and of your whole system.

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