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Power Over Ethernet Interoperability Guide by Sanjaya Maniktala

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Different Ways of Specifying Maximum Operating Temperature
When comparing datasheets, we need to know there are different ways to specify the maximum “operating temperature” of a device. Some vendors take “operating temperature” as the ambient temperature. But some consider this as junction temperature. Customers often get confused by this and tend to think the higher numbers in the latter case implies a better temperature range. Whereas, that may not be so on closer examination. Let us do some estimates to understand this better.
For example, suppose Datasheet A (from Vendor A) states that its recommended range for Chip A is −40° to 85°C—using a 2s2p board as per JESD51-7 guidelines. Whereas Datasheet B for Chip B provides electrical characteristics ...

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