Applicable External DC-DC Converters
www.ti.com
7
Applicable External DC-DC Converters
The external DC-DC converter can be chosen from, but not limited to, the following standard evaluation
boards for quick evaluation tests. The required voltage rating of applicable DC-DC converter is 75V min.
•
LM5005 Evaluation Board, a 2.5A buck regulator for low cost non-isolated PD application (Note: the
LM5005 is a drop-in replacement for the LM5576 on the LM5073 evaluation board).
•
LM5020 Evaluation Board, a current mode flyback converter.
•
LM5025 Evaluation Board, a voltage mode active clamp forward converter.
•
LM5026 Evaluation Board, a current mode active clamp forward converter.
•
LM5032 Evaluation Board, a current mode dual interleaved converter.
•
LM5034 Evaluation Board, a current mode dual interleaved converter with active clamp.
•
LM5115 Evaluation Board, a 5A buck regulator with synchronous rectification.
Note that per IEEE 802.3af the DC-DC converter input capacitor should be at least 5 µF. Considering the
typical capacitor’s tolerance and variations over temperature, a minimum 10 µF nominal is required. This
10 µF minimum value can be combinations of ceramic and electrolytic capacitors for cost considerations.
When the external DC-DC converter’s input capacitance is not enough, C8 of the evaluation board can be
used. Using C8 but excluding L1, JMP6’s three pins should be all shorted together.
8
A Note About the Onboard Buck Regulator
The onboard LM5576 buck regulator is a low cost solution that is ideal for continuous power levels not
greater than 6W. Although the maximum output current is 3.0A maximum power is limited because the
regulator employs a diode in the freewheeling branch, which sacrifices the efficiency under normal 48V
PoE operation. In order to obtain higher efficiency, a synchronous rectification buck regulator like the
LM5115 evaluation board is recommended.
9
Configuration 1: IEEE 802.3af Fully Compliant PD Interface
Figure 2
shows the evaluation board configuration simplified for an IEEE 802.3af fully compliant PD
interface implementation. The following table shows the jumper positions for this configuration.
Table 2. Jumper Positions of Configuration 1
Jumper
Function
JMP4, JMP5
Pins 2 and 3 short, Pin 1 open.
JMP6
Pins 2 and 3 short, Pin 1 open.
JMP7
Pins open.
JMP8
All three pins open.
Jumper pins short when the on-board buck regulator is used.
JMP9, JMP11, JMP12, JMP13
Jumper pins open when an external dc-dc converter is used.
Other Jumpers
Not relevant.
4
AN-1574 LM5073 Evaluation Board
SNVA214A – April 2007 – Revised April 2013
Submit Documentation Feedback
Copyright © 2007–2013, Texas Instruments Incorporated