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Power Over Ethernet Interoperability Guide by Sanjaya Maniktala

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Minimum Inrush Below 30 V
We now know than any typical PSE chip will set its current limit to 425 mA nominal, at about 28 V nominal (< 30 V), as the port voltage ramps up from classification (> 20.5 V) to the commencement of the main inrush phase (> 30 V). But in fact, inrush formally starts just above 20.5 V and the question is: What is the set current limit inside the PSE between 20.5 and 28 V?
As mentioned, the inrush template in Fig. 5.1 applies only above 30 V. So what exactly is allowed below 30 V? The standard actually allows/demands the PSE permit a small inrush current even below 30 V. In Section 33.2.7.5 it states
•  During POWER_UP, for PI voltages between 0 and 10 V, the minimum IINRUSH requirement is 5 mA.
•  During POWER_UP, ...

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