AS1138 Datasheet, PDF (22/30 Pages) List of Unclassifed Manufacturers – 30W PoE PD and DC-DC Controller

AS1138
POE POWER-ON STARTUP WAVEFORM
Figure 29 represents the power-on sequence for PoE operation. The waveform reflects typical voltages present at the PD during
signature, classification and power-on.
Figure 30 - 802.3at Typical Power-On Waveform
1. Voltages V1 and V2 are applied by the PSE to extract a signature value.
2. The PSE takes current/impedance readings during Class/Mark Events to determine the class of the PD. At this time, the PD
presents a load current determined by the resistance connected to the RCLASS pin.
3. After the PSE measures the PD load current, if it is a high-power PSE, it presents a mark voltage (6.9-10V), followed by a second
classification voltage. The PD responds by presenting a load current as determined by the resistor on the RCLASS pin. After the PSE
measures the PD load current the second time and determines that is can deliver the requested power, it moves into the On state by
raising the voltage to approximately 42V.
Akros Silicon, Inc.
6399 San Ignacio Avenue, Suite 250, San Jose, CA 95119 USA
408.746.9000 www.AkrosSilicon.com
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