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General Design Considerations
5.1.3
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Rules of thumb
Assuming the recommended 100 °C junction temperature limit, the following rules of thumb can be
provided, which are based on Hilscher’s design experience with netX chips:
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Designs with 45 x 60 mm area and heat sink usually work up to 70 °C.
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Designs with 45 x 60 mm area without heat sink usually work up to 55 °C.
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netX500 designs with 30 x 50 mm and heat sink usually work up to 70 °C.
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When using the internal PHYs, the netX temperature rises by appr. 15 °C.
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When using the heat sinks, recommended by Hilscher, the maximum temperature of the
netX case decreases by approximately. 15 °C.
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The above rules assume unimpeded convection of the PCB. When a small closed cabinet
is used, the maximum ambient temperature (inside the cabinet) must be decreased by
approximately 15 °C.
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When the power density is higher than 0.15 W/cm², it will be critical to make a netX design
which operates up to 70 °C.
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Avoid placing semiconductor components on the bottom side of the PCB within the netX
chip area. Resistors or ceramic capacitors may be placed under the netX if they allow
operating temperatures up to 100 °C (X7R ceramic).
Temperature tests with a netX500 Evaluation board have shown, that it is possible to build designs
for extended temperature range (up to +85 °C) with heat sink, resulting in a netX case temperature
of ~103 °C (see document “nxdkn-en_Rev3_Waerme.pdf”, available on the Hilscher website).
netX Design-In Guide | netX 100/500
DOC081106AN02EN | Revision 2 | English | 2012-10 | Released | Public
© Hilscher, 2008-2012