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Power Over Ethernet Interoperability Guide by Sanjaya Maniktala

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Practical PSE Design for Inrush Currents
In Fig. 5.2 we present the AT standards’s inrush template (worst-case, extracted from Fig. 5.1). This figure now also includes the lower current-limit threshold (0.4 A), and also the minimum value of the inrush timer (50 ms). So this is complete, and it is the AT (more stringent) requirement. A practical PSE design will center its inrush current limit between 400 and 450 mA. So its nominal value will be about 425 mA, but there will be a spread around that, based on various tolerances and drifts. This band of uncertainty is shown in gray in the figure. But keep in mind that the minimum of this tolerance band must be above 400 mA, and it maximum must be below 450 mA. Similarly there is another gray region ...

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