LINEAR dn425f Product Specifications
Summary
A powerful PD interface solution for modern high-power Ethernet systems. This controller manages power delivery up to 35W, solving limitations found in standard PoE applications requiring higher wattage. The manual details how its integrated flyback topology efficiently regulates power, mitigating current imbalance issues common in multi-pair installations. Ideal for engineers developing advanced networking devices that require reliable, high-efficiency power from both dedicated PSEs and optional auxiliary supplies.
Page 1 Text Content
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High Power Po E PD Interface with Integrated Flyback Controller Design Note 425 Dilian Reyes Introduction PSE that looks for such a class. Once a PSE detects
To this day, Power over Ethernet (Po E) continues to gain and classifi es the PD, it fully powers on the device. The popularity in today’s networking world. The 12.95W LTC4268-1 provides a low inrush current limit, allow- delivered to the Powered Device (PD) input supplied by ing load capacitance to ramp up to the line voltage in the Power Sourcing Equipment (PSE) is a universal sup- a controlled manner without interference from the PSE ply. Each PD provides its own DC/DC conversion from a current limit. After the load capacitance is charged up, the nominal 48V supply, thus eliminating the need for a cor- LTC4268-1 switches to the high input current limit and rect voltage wall adapter. However, higher power devices provides a power good signal to its switching regulator can not take advantage of standard Po E because of its indicating that it can start its operation. During this time, power limitations, and must rely on a large wall adapter the LTC4268-1 remains in its high current limit state al- as their primary supply. The new LTC4268-1 breaks this lowing for up to 35W delivered to the load.
power barrier by allowing for power of up to 35W for such
Synchronous Flyback Controller
power-hungry 2-pair Po E applications. The LTC4268-1
Once power is switched over to the synchronous fl yback
provides a complete solution by integrating a high power
controller, the LTC4268-1 regulates the output voltages
PD interface control with an isolated fl yback controller.
by sensing the average of all the output voltages via a
PD Interface Controller transformer winding during the fl yback time. This al-
The PD interface controller provides the same 25k sig- lows for tight output regulation without the use of an
nature detection resistance defi ned in the standard Po E.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. An extended optional class can be read by a customized All other trademarks are the property of their respective owners.
T1 L1 PA1558NL 0.33μH
Q1 10Ω C1A C1B Si4470EY 1/4W
SMAJ58A 10Ω 11.8V
C7 C11 0.4AC10
Po E+ 1000p F
0.1μF BAS21
R10 Si4488DY
Po E– 0.33μH
Si4488DY 47μF
FMMT723 100μF
PWRGD PWRGD UVLO FB PGVCCILIM_EN
VPORTP R13
4.7k SENSE+ RSENSE Si4362DY
SENSE– 1% 47Ω
LTC4268-1 FMMT718 FMMT618
SG C24
SHDN R17 1μF
100k RCLASS VCMP C27 2200p F 15Ω C33 0.1μF
VPORTNVPORTNVPORTN PGDLYVNEGVNEGVNEG t ON SYNC RCMP ENDLY OSC SFST CCMP GND
AUX+ R21 RCLASS Rt ON RCMP R27 T2 D14 R28 20k RPGDLY 100k 2.1k RENDLY COSC CCMP 10k C26 PA0184 BAT54 10k
0.033μF dn425 F01
D12 CSFST B2100
C23 4700p F 250VAC
Figure 1. High Effi ciency, Triple Output, High Power PD
Page Summary Contents For LINEAR dn425f Product Specifications
Manual Details
| Brand | Linear |
|---|---|
| Pages | 2 |
| File Size | 91.06 KB |
| Published | May 31, 2026 |
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Frequently Asked Questions
What is the primary function of the LTC4268-1?
It is a high-power, triple output PD controller with an integrated flyback topology and synchronous rectification for efficient high power delivery via both PoE and auxiliary supplies.
How does the LTC4268-1 address current imbalance in 4-pair systems?
The architecture uses two independent LTC4268-1s to monitor and control power, resolving the issue of uneven current distribution across Ethernet pairs.
What is the maximum achievable power for a PD using this device?
It can support up to 35W delivered to the load when utilizing its synchronous flyback controller.
Does the device require an optoisolator or external complexity?
No, the LTC4268-1 is designed to eliminate the need for separate components like optoisolators by integrating a complete solution within one chip.