www.ti.com
Usage Setup and Test Procedure
have JMP4 and JMP5’s pins 1 and 2 shorted but pin 3 open.
•
An input differential mode filter. To select this feature, have JMP6’s pins 1 and 2 shorted but pin 3
open.
•
Aux dominance feature. It only applies to Rear Aux power operation. To select Aux dominance, short
JMP1. Normally D4 pads are shorted. When the protection of the RAUX pin against negative voltage
application, install D4 of an appropriate voltage rating.
•
Additional input capacitor C8 to meet the minimum 10µF requirement for PoE operation. Using C8 but
excluding L1, JMP6’s three pins should be all shorted together.
For applications which requires multi features of the previous configurations, simply combine those
configurations. For example, to support both FAUX and RAUX power options, combine
Figure 3
and
Figure 4
; for a non-isolated solution that supports both PoE and RAUX power options, combine
Figure 4
and
Figure 5
, and so on.
14
Usage Setup and Test Procedure
14.1 Load Connection
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 recommended not 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.
For the output load connection of either the onboard buck regulator or an external DC-DC converter,
sufficiently large wire, such as AWG #18 or thicker, is required. 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.
14.2 Source Power
To fully test the evaluation board for high power PD applications, either a high power PSE able to supply
adequate power or a bench DC power supply capable of at least 60V and 1A is required for the PoE input.
For the FAUX and RAUX source power, a DC power supply capable of 30V and 3A can be used. Use the
output over-voltage and over-current limit features of the bench power supplies to protect the board
against damage by errant connections.
14.3 Faux Power Option
The auxiliary power source feeding into the FAUX input passes through the LM5073’s hot swap MOSFET,
and the inrush and dc current limits apply. Therefore, the applicable FAUX power voltage depends on the
output power requirement. For the IEEE 802.3af specified maximum power intake of 12.95W, the FAUX
power option will be limited to an auxiliary voltage source of 20V or higher. When the power level is lower
or higher, the applicable FAUX power source voltage will be lower or higher, determined by the output
power, conversion efficiency, and the 800mA maximum dc current limit of the LM5073.
14.4 RAUX Power Option
An auxiliary power source of 10V to 57V can feed into the RAUX input. However, the simple RAUX input
inrush limiter resistor for lower than 24V RAUX source will not be efficient, and the previously mentioned
MOSFET type inrush limit will be required.
If the RAUX power source is below the minimum startup input voltage of the DC-DC converter, the startup
bias voltage (normally Vcc) can be obtained directly from the RAUX input. A simple approach is to feed
the RAUX input through a 20
Ω
resistor and a diode to the Vcc rail of the DC-DC converter for startup.
However, when the RAUX power source voltage is higher than the maximum rating of the VCC pin of the
DC-DC converter’s controller, this RAUX feed into VCC rail must be disconnected.
9
SNVA214A – April 2007 – Revised April 2013
AN-1574 LM5073 Evaluation Board
Submit Documentation Feedback
Copyright © 2007–2013, Texas Instruments Incorporated