QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1351A
SINGLE OUTPUT, HIGH POWER, HIGH EFFICIENCY POE
1
LTC4269IDKD-2
DESCRIPTION
Demonstration circuit 1351A is a high-power supply
featuring the LTC
®
4269IDKD-2. This board acts as
an IEEE 802.3at compliant, high power Power-over-
Ethernet (PoE), Powered Device (PD) and connects
at the RJ45 to a compatible high power Power
Sourcing Equipment (PSE) device, such as the
DC1366A.
The LTC4269IDKD-2 provides IEEE802.3at standard
(PoE+) PD interfacing and power supply control.
When the PD is fully powered, the PD interface
switches power over from the PSE to the switcher
through an internal, low resistance, high power
MOSFET. The highly integrated LTC4269IDKD-2 con-
trols a high-power, small-sized power supply that
utilizes a highly-efficient isolated forward topology
with synchronous rectification. The DC1351A sup-
plies a 5V output at up to 5A.
DC1351A also demonstrates the use of an auxiliary
48V wall adapter. When present, the auxiliary supply
becomes the dominant supply over PoE to provide
power.
Design files for this circuit board are available.
Call the LTC factory.
,
LTC and LT are registered trademarks of Linear Technology Corporation.
Table 1.
Performance Summary (T
A
= 25°C)
PARAMETER
CONDITION
VALUE
Port Voltage (V
PORT
)
At Ethernet port
37V – 57V
Auxiliary Voltage (V
AUX
)
From Aux- to Aux+ terminals
44V – 57V
Output Voltage (V
OUT
) Initial Set-point
V
PORT
= 37V to 57V, I
OUT
= 0A to 5A
5.05V ± 1%
Maximum Output Current
V
PORT
= 42V
4.6A (min)
Typical Output Voltage Ripple
V
IN
= 50V, I
OUT
= 4.6A
40mV
P–P
(typ)
Output Regulation
Over Entire Input Voltage and Output Current Range
< ±0.1% (typ)
Peak to Peak Deviation with Load Step of 2.5A to 5A
±120mV (< ±2.5%) (typ)
Load Transient Response
Settling Time (within 1% of V
OUT
)
150us (typ)
Switching Frequency
225kHz (typ)
Efficiency
VPORT = 42V, IOUT = 5A, not incl. diode bridge
92.5% (typ)
OPERATING PRINCIPLES
A compatible high power PSE board, such as the
DC1366A, is connected to the DC1351A at the RJ45
connector J2 (see the schematic). As required by
IEEE802.3at, a diode bridge is used across the data
pairs and signal pairs. Schottky diodes (D5-8, D12-
15) are used at the input to improve efficiency over
standard diode bridges. The LTC4269IDKD-2 pro-
vides an IEEE802.3at standard PoE 25k signature re-
sistance and is set for a power class 4. When the PD
is powered and voltage is above the PoE ‘‘On Volt-
age’’, the LTC4269IDKD-2 switches the port voltage
over to the power supply controller through its inter-