LM5070 Reference Design - Isolated Power-over-Ethernet (POE) Regulator, Low-cost, High Efficiency 5V 7W Output
  Design Specifications
Inputs Outputs #1
VinMin=-57 Vout1=5.0
VinMax=-36 Iout1=1.4
   Design Resources
LM5070 Reference Design

  Additional Resources

•LM5070 Product Folder
•LM5070AE EVAL Evaluation Board
•LM5070HE EVAL Evaluation Board
    Bill Of Materials
Part Manufacturer Part# Attributes
C1 TDK C4532X7R2A225 2.2u F
C10 Vitramon VJ0805Y102KXAAT 1n F
C14 TDK C3216X5R0J106K 10u F
C15 TDK C3216X5R0J106K 10u F
C16 Sanyo 6CV390EX 390u F
C18 Vitramon VJ0805Y101KXAAT 100p F
C19 Vitramon VJ0805Y473KXAAT 4.7n F
C2 TDK C4532X7R2A225 2.2u F
C21 TDK C2012X5R1A105K 1u F
C22 Vitramon VJ0805Y103KXAAT 10n F
C23 SYFER 1808JA250102KXBSY2 1n F
C3 TDK C4532X7R2A225 2.2u F
C4 Vitramon VJ0805Y104KXAAT 0.1u F
C5 Vitramon VJ0805Y224KXAAT 0.22u F
C6 Vitramon VJ0805Y104KXAAT 0.1u F
C7 Vitramon VJ0805Y473KXAAT 47n F
C9 TDK C2012X5R1A105K 1u F
D1 Diodes HD01 1 V
D2 Diodes HD01 1 V
D3 Fairchild MMSD4148 1 V
D5 IR 12CWQ03 0.47 V
DZ1 Diodes SMAJ60A
J1 SAMTEC MODS-A-8P8C-X
L1 Coilcraft DO1813P-181HC 0.18u H, 0.003 Ohms
M1 Vishay SI4848DY
R1 Dale CRCW08051001FRT6 1k Ohms
R10 Dale CRCW08051073FRT6 107k Ohms
R13 Dale CRCW080520R0FRT6 20 Ohms
R14 Dale CRCW08051212FRT6 12.1k Ohms
R16 Dale CRCW080510R0FRT6 10 Ohms
R17 Dale CRCW08052212FRT6 22.1k Ohms
R18 Dale CRCW08057321FRT6 7.32k Ohms
R19 Dale CRCW08055112FRT6 51.1k Ohms
R2 Dale CRCW08055903FRT6 590k Ohms
R20 Dale CRCW08055900FRT6 590 Ohms
R23 Dale CRCW08051001FRT6 1k Ohms
R3 Dale CRCW08053322FRT6 33.2k Ohms
R5 Dale CRCW08052492FRT6 24.9k Ohms
R6 OPEN OPEN
R7 Dale CRCW08051000FRT6 100 Ohms
R8 Dale CRCW12060R60FRT6 0.6 Ohms
T1 Coilcraft C1588-A
U1 National Semiconductor LM5070
U2 NEC PS2501L-1-H
U3 National Semiconductor LMV431

  Design Description
This design utilizes the LM5070 configured in a non-synchronous, flyback topology and operating in continuous conduction mode (CCM), to offer a low-cost, high efficiency solution for Power-over-Ethernet (PoE) applications*. The LM5070 is a dedicated PoE powered device (PD) interface/PWM controller that integrates all the power sequencing, control mode, and fault protection necessary to comply with the IEEE 802.3af specification for power sourcing equipment (PSE).

This isolated PoE design operates at 260kHz and uses a custom PoE transformer to convert the input voltage, via flyback action, to an output voltage level of 5V at 1.4A (7W). The primary side bias is derived from an auxiliary winding after successful start-up occurs. The secondary side feedback components are selected appropriately to ensure proper gain and phase margins for stable operation and quick transient response.

* Refer to POWER Designer, No. 104 (http://www.national.com/an/AN/AN-1358.pdf) or the LM5070 Evaluation Board - Application Note 1358 (http://www.national.com/appinfo/power/files/PowerDesigner_104.pdf) for more information on Power Supply Design for PoE Applications.



  Schematic
Example Schematic Showing Connection for all Components.


  Layout

Board's Bottom View
Board's Top View

  Waveforms

Start-up@full load constant resistance
Sw pin waveforms
Transient Response
Turn-off at full load constant resistance load
Vin = 57V waveforms
bode plot