LM5072EVAL/NOPB National Semiconductor, LM5072EVAL/NOPB Datasheet - Page 11

• Manufacturer Part Number: LM5072EVAL/NOPB
• Description: EVAL BOARD FOR LM5072
• Manufacturer: National Semiconductor

Specifications of LM5072EVAL/NOPB

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Modes of Operation
Per the IEEE 802.3af specification, when a PD is connected
to a PoE system it transitions through several operating
modes in sequence including detection, classification (op-
tional), turn on, normal operation, and power removal. Each
operating mode corresponds to a specific PoE voltage range
fed through the Ethernet cable. Figure 3 shows the IEEE
802.3af specified sequence of operating modes and the cor-
responding PD input voltages.
Current steering diode-bridges are required for the PD inter-
face to accept all allowable connections and polarities of PoE
Detection (Signature)
Mode of Operation
Normal Operation
Classification
Startup
TABLE 1. Operating Modes With Respect To Input Voltage
FIGURE 3. Sequence of PoE Operating Modes
Voltage from PoE Cable per
14.5V to 20.5V
2.7V to 10.0V
IEEE 802.3af
57V to 36V
42V max
11
voltage from the RJ-45 connector (see the example applica-
tion circuits in Figures 18, 19, 20 and 21). The bridge will
cause some reduction of the input voltage sensed by the
LM5072. To guarantee full compliance to the specification in
all operating modes, the LM5072 takes into account the volt-
age drop across the bridge diodes and responds appropri-
ately to the voltage received from the PoE cable. Table 1
presents the response in each operating mode to voltages
across the VIN and VEE pins.
38V (UVLO Release, V
70V to 32V (UVLO, V
LM5072 Input Voltage
(V
IN
1.5V to 10.0V
12V to 23.5V
20184617
pin to V
EE
pin)
IN
IN
Falling)
Rising)
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