Classification; Start-Up; Operation - Planet Switch User Manual

Industrial Renewable Energy 4-Port 10/100/1000T
802.3at PoE+ Managed Ethernet Switch/Router
BSP-360

6.2 Classification

Once a PD is detected, the PSE may optionally perform classification to determine the maximal power a PD is
to consume. The PSE induces 15.5-25.5V DC, limited to 600 mA, for a period of 10 to 75 ms responded by a
certain current consumption by the PD, indicating its power class.
The PD is assigned to one of 5 classes: 0 (default class) indicates that full 15.4 watts should be provided, 1-3
indicate various required power levels and 4 has a power range of 12.95 – 25.5 watts. PDs that support
classification are assigned to class 0. Special care must be employed in the definition of class thresholds, as
classification may be affected by cable losses.
Classifying a PD according to its power consumption may assist a PoE system in optimizing its power
distribution. Such a system typically suffers from lack of power resources, so that efficient power management
based on classification results may reduce total system costs.

6.3 Start-up

Once line detection and optional classification stages are completed, the PSE must switch from low voltage to
its full voltage capacity (44-57 Volts) over a minimal amount of time (above 15 microseconds).
A gradual startup is required, as a sudden rise in voltage (reaching high frequencies) would introduce noise
on the data lines.
Once provision of power is initiated, it is common for inrush current to be experienced at the PSE port, due to
the PD's input capacitance. A PD must be designed to cease inrush current consumption (of over 350 mA /
600mA) within 50 ms of power provision startup.

6.4 Operation

During normal operation, the PSE provides 44-57 VDC, able to support a minimum of 15.4watt / 25.5-watt
power.
Power Overloads
The IEEE 802.3af / IEEE 802.3at standard defines handling of overload conditions. In the event of an
overload (a PD drawing a higher power level than the allowed 12.95 watts / 25.5 watts), or an outright short
circuit caused by a failure in cabling or in the PD, the PSE must shut down power within 50 to 75 milliseconds,
while limiting current drain during this period to protect the cabling infrastructure. Immediate voltage drop is
avoided to prevent shutdown due to random fluctuations.
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