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dc2046aaf

DEMO MANUAL DC2046A-A

Description

LT4276, LT4321

PoE PD with Synchronous

Flyback and Ideal Diode Bridge

Demonstration circuit 2046A-A is a PoE powered device

(PD) with an isolated power supply using synchronous

flyback topology, featuring the LT®4276 and ideal diode

bridge controller (LT4321).

The LT4276 provides IEEE802.3af (PoE, Type 1),

IEEE802.3at(PoE+,Type2),andLTPoE++™PDinterfacing

and power supply control. When the PD is fully powered,

the PD interface switches power over from the power

sourcing equipment (PSE) to the switcher through an

external, low resistance, high power N-channel FET. The

highly integrated LT4276 controls a high power, small-

sized power supply that utilizes a highly efficient flyback

L

, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and

LTPoE++ is a trademark of Linear Technology Corporation. All other trademarks are the property

of their respective owners.

performance summary

BoarD photos

topology with synchronous rectification. The LT4321

provides further efficiency improvement by minimizing

the bridge losses.

The DC2046A-A supplies a 3.3V output at up to 6.8A. It

also demonstrates the use of an optional auxiliary power

supply input of 48V. When present, the auxiliary supply

becomes the dominant supply over PoE to provide power.

Design files for this circuit board are available at

http://www.linear.com/demo/DC2046A-A

Top Side

Bottom Side

PARAMETER

CONDITIONS

VALUE

At Ethernet Port

37V to 57V

Auxiliary Voltage

37V to 57V

Output Voltage

3.3V (Typ)

Output Current

6.8A (Max)

Output Voltage Ripple

Output Regulation

±0.15% (Typ)

Efficiency

90% (Typ)

Switching Frequency

250kHz (Typ)