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PoE Performance Characteristics
Horizontal Resolution: 1 µs/div.
Trace 1: Current sense voltage across RE15. 0.5V/div.
Trace 2: The input current from the AUX power source. 200 mA/div
Figure 7. Cycle-by-cycle Peak Current Limit under AUX Input and Output Dead Short Condition
Horizontal Resolution: 1 µs/div.
Trace 1: Current sense voltage across RE15. 0.5V/div.
Trace 2: The input current from the AUX power source. 100 mA/div
Figure 8. Cycle-by-cycle Peak Current Limit under 48V PoE Input and Output Dead Short Condition
Figure 9
shows key waveforms of over-current protection by the hot swap MOSFET’s dc current limit. The
PoE input voltage is at 38V. The input current exceeds the 800 mA current limit of the hot swap MOSFET,
and causes the voltage at the RTN pin to rise rapidly. It also discharges the soft start capacitor CE26
connected to the SS pin, and the circuit enters the automatic retry mode as long as the over-current
condition is present.
13
SNOA476C – October 2006 – Revised April 2013
AN-1521 POEPHYTEREV-I / -E Evaluation Board
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