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Manual
LM5072 5V out 25W IEEE
802.3at Compliant POE+ PD
Power Eval_Board
1.0 Design Specifications
2.0 Design Description
Eval Board Description
This LM5072 based 5V out 25W POE+ PD power supply is
fully compliant with IEEE 802.3at standard. This eval board
converts 48 Vdc to 5 Vdc. It can deliver up to 25W power as
specified by the IEEE 802.3at standard. It has a 2 event de-
tection circuit which can identify the PSE as either Type one
or Type two. ( See National Semiconductor Application note
"Fully Compliant IEEE 802.3at Interface Using the LM5072/
LM5073" for details ) The 2 event detection circuit is located
on the bottom layer of the PC board. In those applications
where this 2 event detection feature is not required, the user
only needs to populate top layer components.
The input current limit is 800 mA. The efficiency of this eval
board is high enough to keep input current under 800mA at
38Vin full load. The input under voltage lock has 7V hystere-
sis, with 38V rise and 31V fall. This eval board also has output
short circuit protection.
This eval board can also be powered by a 24V AUX power
supply. In this configuration, the AUX input port bypasses the
LM5072 internal hot swap MOSFET and allows input current
to be greater than the 800 mA limit.
LM5072
The LM5072 Powered Device (PD) interface and Pulse-
Width-Modulation (PWM) controller provides a complete pow-
er solution for the PD connecting into Power over Ethernet
(PoE) networks. This controller integrates all functions nec-
essary to implement both a PD powered interface and DC-DC
4.0 Schematic
© 2009 National Semiconductor Corporation
Inputs
Output #1
VinMin=38V
Vout1=5V
VinMax=60V
Iout1=5A
National Semiconductor
RD-180
PowerWise Design Center
November 16, 2009
converter with a minimum number of external components.
The low RDS(ON) PD interface hot swap MOSFET and pro-
grammable DC current limit makes LM5072 suitable for both
IEEE 802.3af and IEEE 802.3at compliant PD devices. The
100V maximum voltage rating simplifies selection of the tran-
sient voltage suppressor that protects the PD from network
transients. The LM5072 includes an easy to use PWM con-
troller. The PWM control scheme is based on peak current
mode control, which provides inherent advantages of line
feed forward, cycle by cycle current limit and simplifies feed-
back loop compensation.
IEEE 802.3af and IEEE 802.3at are the PoE specifications
this design is compliant with.
3.0 Features
■
DC/DC converter efficiency of 85% at 48V in 25W load
■
With added two event detection circuit, this design is fully
compliant with IEEE 802.3at
■
Integrated POE+ RJ45 magetics connector provides
Ethernet isolation
■
Low ripple voltage <20 mV, tight dynamic load regulation
<75 mV
■
Inrush current limit, 800 mA input over current protection
■
Output short circuit protection, soft start, input under
voltage protection
■
24V AUX input port with Oring diode
■
Uses standard FA2898-AL transformer from Coilcraft
www.national.com
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Related Manuals for National Semiconductor LM5072
Summary of Contents for National Semiconductor LM5072
- Page 1 Eval Board Description sient voltage suppressor that protects the PD from network This LM5072 based 5V out 25W POE+ PD power supply is transients. The LM5072 includes an easy to use PWM con- fully compliant with IEEE 802.3at standard. This eval board troller.
- Page 2 other2 FIGURE 1. Schematic_sheet1 www.national.com...
- Page 3 schematic15 FIGURE 2. Schematic_sheet2 www.national.com...
- Page 4 schematic17 FIGURE 3. Schematic_sheet3 www.national.com...
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Page 5: Bill Of Materials
Resistor 0805 5%, 0.125W Vishay-Dale CRCW08050000Z0EA T100 Transformer EFD20 Coilcraft FA2898-AL U100 MiscPower MXA16A Integrated 100V POE Controller National Semiconductor LM5072MH-80 U101 OPTOCOUPLER PS2501L-1 PS2501L-1-H U102 Shunt Regulator SOT23-5 LOW VOLTAGE ADJ SHUNT National Semiconductor LMV431AIM5 U200 Comparator IC M08A_L... -
Page 6: Quick Start
6.0 Other Operating Values Operating Values Description Parameter Value Unit Modulation Frequency Frequency Total output power Pout Steady State Efficiency Efficiency Control scheme Control scheme Current Mode Peak-to-peak ripple voltage Vout p-p Static load regulation Static load Dynamic load regulation Dynamic load 7.0 Board Photos boardphoto1... - Page 7 eval board to the negative terminal of the electronic load. Set 2. Plug Ethernet cable to J300 on the eval board. electronic load current to 5A. 3. Connect test point P102 on the eval board to the positive 3. Turn on the PSE. terminal of the electronic load.
- Page 8 DC/DC Converter Efficiency vs POE input voltage ( Not including the diode bridges ) Vin (V) Iin (A) Pin (W) Vout (V) Iout (A) Pout (W) Ploss (W) Efficiency (%) 0.77 29.26 4.916 24.58 4.68 84.01 0.729 29.16 4.917 24.585 4.575 84.31 0.693...
- Page 9 DC/DC Converter Efficiency vs AUX port input voltage ( Including Oring diode ) Vin (V) Iin (A) Pin (W) Vout (V) Iout (A) Pout (W) Ploss (W) Efficiency (%) 1.549 30.98 4.921 24.605 6.375 79.42 1.385 30.47 4.918 24.59 5.88 80.70 1.254 30.096...
- Page 10 waveform FIGURE 8. Output Ripple and Noise www.national.com...
- Page 11 waveform1 FIGURE 9. Load Transient Response 10.0 Layouts www.national.com...
- Page 12 layout6 FIGURE 10. PCB TOP www.national.com...
- Page 13 layout7 FIGURE 11. PCB BOTTOM www.national.com...
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Page 14: Life Support Policy
Notes National Semiconductor's design tools attempt to recreate the performance of a substantially equivalent physical implementation of the design. Reference designs are created using National's published specifications as well as the published specifications of other device manufacturers. While National does update this information periodically, this information may not be current at the time the reference design is built. -
Page 15: Important Notice
IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, modifications, enhancements, improvements, and other changes to its products and services at any time and to discontinue any product or service without notice. Customers should obtain the latest relevant information before placing orders and should verify that such information is current and complete.