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Connection and Proper Test Methods
Figure 4. The Connection Ports of the Evaluation Board
The -E version evaluation board employs a regular RJ45 connector, J13, which is to be used with the
external Ethernet magnetics assembly U4. The -I version evaluation board uses an integrated RJ45
connector, UE13, which has the Ethernet magnetics enclosed in the case.
For the PoE input through either RJ45 connector, the diode bridge BR1 or BR2 is used to steer the current
to the positive and negative supply pins of the LM5072, namely the VIN and VEE pins. When using TP7
and TP8 for the quick PoE input connection to a bench power supply, make sure TP7 is the high potential
terminal.
For the AUX power input, the higher potential should feed into the center pin of P1. When using TP3 and
TP4 for the quick AUX input connection to a bench power supply, be aware that TP3 is the high potential
pin. The diode DE1 provides the reverse protection of the AUX input.
Please note that TP4 and TP8 are two different return pins for the PoE and AUX inputs, respectively. They
are not connected to the same circuit node, and they should not be interchanged.
For the output connection, the load can be either a passive resistor or active electronic load. Attention
should be paid to the output polarity when connecting an electronic load. It is not recommended to use
additional filter capacitors greater than 20 µF total across the output port as the extra capacitance will alter
the feedback loop properties and may cause instability. If it is necessary to add extra capacitance in a
particular application, the feedback loop compensation must be adjusted accordingly.
Sufficiently large wire such as AWG #18 or thicker is required when connecting the source supply and
load. Also, monitor the current into and out of the circuit board. Monitor the voltages directly at the board
terminals, as resistive voltage drops along the connecting wires may decrease measurement accuracy.
Never rely on the bench supply’s voltmeter or ammeter if accurate efficiency measurements are desired.
When measuring the dc-dc converter efficiency, the converter input voltage should be measured across
CE4. When measuring the evaluation board overall efficiency (which is more relevant), both input and
output voltages should be read from the terminals of the evaluation board. Remember to count the power
dissipation by the PHY circuit in the efficiency measurement. When the PHY circuit is in the idle mode, it
will draw 55 mA from the 3.3V rail, most of which is consumed by the on-board LED indicators.
Refer to the appropriate user manual or instruction for the use of the MII connector.
7
SNOA476C – October 2006 – Revised April 2013
AN-1521 POEPHYTEREV-I / -E Evaluation Board
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