LM5071HEEVAL National Semiconductor, LM5071HEEVAL Datasheet - Page 4

• Manufacturer Part Number: LM5071HEEVAL
• Manufacturer: National Semiconductor

Specifications of LM5071HEEVAL

• Lead Free Status / Rohs Status: Not Compliant

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Power Up
is observed, it is likely that the AUX power feed polarity is
reversed. After successful operation is observed, full power
testing can begin.
PD Interface Operating Modes
When connecting into the PoE system, the evaluation
board’s Powered Device interface will go through the follow-
ing operating modes in sequence: PD signature detection,
power level classification (optional), and application of full
power. Refer to the LM5071 datasheet and IEEE 802.3af for
detailed information about these operating modes.
Signature Detection
On the evaluation board, the PD signature is implemented
with R13. The use of a 26.1 kΩ resistor for R13 yields an
Class
0
1
2
3
4
(Continued)
Reserved
0.44W
0.44W
3.84W
6.49W
P
MIN
Reserved
12.95W
12.95W
3.84W
6.49W
P
MAX
I
CLASS
4
17mA
26mA
36mA
0mA
9mA
equivalent signature impedance of 25.1kΩ, which is in the
valid PD signature range of 23.75 kΩ to 26.25 kΩ per IEEE
803.2af.
It should be noted that when the AUX power is present, it will
not allow the PoE’s power sourcing equipment (PSE) to
identify the PD as a valid device, because the AUX voltage
will cause the front-end current steering diode bridges to be
reverse biased during detection mode. This prevents the
PSE from applying power, and the evaluation board only
draws current from the AUX source.
Classification
PD classification is implemented with R22. The evaluation
board is set to the default Class 0 by leaving the RCLASS
pin open (R22 position not populated). To activate a specific
class instead of Class 0, install R22 according to the follow-
ing table.
(MIN)
I
CLASS
12mA
20mA
30mA
44mA
4mA
(MAX)
R22 Selection
82.5Ω
53.6Ω
38.3Ω
Open
150Ω