DEMO MANUAL
DC2475A-A
LT4295, LT4321
High Efficiency IEEE802.3bt (PoE
40W) PD with PoE Ideal Diode Bridge
Description
Demonstration circuit 2475A-A is an IEEE802.3bt (Draft 2.0)
compliant Power over Ethernet (PoE) powered device(PD).
It features the LT
controller with the LT4321 PoE ideal diode bridge controller.
The LT4295 provides IEEE802.3af (PoE, Type 1),
IEEE802.3at (PoE+, Type 2), and IEEE802.3bt (PoE++,
Type3 and 4) compliant interfacing and power supply
control. It utilizes an external, low R
cal) N-channel FET for the Hot Swap function to improve
efficiency. The
utilizes a highly efficient flyback topology with synchro
nous rectification.
The LT4321 controls eight low R
N-channel FETs to further improve end-to-end power
®
4295 PD interface and switching regulator
(57mΩ typi-
DS(ON)
LT4295 controls a DC/DC converter that
-
(57mΩ typical)
DS(ON)
++
, Type
3,
delivery efficiency and ease thermal design. This solution
replaces the eight diodes typically found in a passive PoE
rectifier bridge.
The DC2475A-A accepts up to 40W of delivered power
from a power sourcing equipment (PSE) via the RJ45
connector (J1) or a local 48VDC power supply using the
auxiliary supply input. When both supplies are connected,
the auxiliary supply input has priority over the PoE input.
The DC2475A-A supplies a 12V output at up to 3A.
Design files for this circuit board are available at
http://www.linear.com/demo/DC2475A-A
L, LT, LTC, LTM, Linear Technology, the Linear logo and LTPoE++ are registered trademarks of
Analog Devices, Inc. All other trademarks are the property of their respective owners.
performance summary
PARAMETER CONDITIONS VALUE
Port Voltage (V
Auxiliary Voltage From AUX
Output Voltage (V
Output Current (I
Output Voltage Ripple V
Load Regulation ±0.1% (Typical)
Efficiency V
Switching Frequency 250kHz (Typical)
) At RJ45 37V to 57V
PORT
) 12V (Typical)
OUT
) 3A (Max)
OUT
PORT
PORT
+
to AUX– Terminals 37V to 57V
= 44V, I
= 50V, I
= 3A 85mV
OUT
= 3A, End-to-End 92% (Typical)
OUT
(Typical)
P-P
BoarD photo
Top Side
Bottom Side
dc2475aafb
1
DEMO MANUAL
LOAD CURRENT (A)
0
0.511.522.5
3010
2030405060708090100
EFFICIENCY (%)
DC2475AA F02
LOAD CURRENT (A)
0
0.511.522.5
3
11.80
11.85
11.90
11.95
12.00
12.05
12.10
12.15
12.20
V
OUT
(V)
DC2475AA F03
DC2475A-A
typicaL performance characteristics
Top Side
Figure 1. Thermal Pictures (Conditions: V
V
PORT
44V
50V
57V
Figure 2. Efficiency (End-to-End)
PORT
Bottom Side
= 44V, V
OUT
= 12V, I
Figure 3. Load Regulation
OUT
= 3A)
V
PORT
44V
50V
57V
2
dc2475aafb
typicaL performance characteristics
DEMO MANUAL
DC2475A-A
Figure 4. Switch Node Waveforms (Conditions: V
PORT
= 57V, V
OUT
= 12V, I
OUT
= 3A)
Figure 5. Output Voltage Ripple (Conditions: V
PORT
= 44V, V
OUT
= 12V, I
OUT
= 3A)
dc2475aafb
3
DEMO MANUAL
DC2475A-A
typicaL performance characteristics
Figure 6. Load Transient Response (Conditions: V
= 44V, Load Step: 1.5A to 3A to 1.5A)
PORT
Figure 7. Gain and Phase Margin of the Flyback DC/DC Converter (Conditions: V
CROSSOVER FREQUENCY (kHz) GAIN MARGIN (dB) PHASE MARGIN (deg)
5 20 64
4
PORT
= 44V, V
OUT
= 12V, I
OUT
= 3A)
dc2475aafb
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