QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1335A-B
HIGH POWER, HIGH EFFICIENCY POE PD INTERFACE WITH INTEGRATED SWITCHING
REGULATOR
1
LTC4269IDKD-1
DESCRIPTION
Demonstration circuit 1335A-B is a high-power sup-
ply featuring the LTC
®
4269IDKD-1. This board acts
as an IEEE 802.3at compliant, high power Power-
over-Ethernet (PoE), Powered Device (PD) and con-
nects at the RJ45 to a compatible high power Power
Sourcing Equipment (PSE) device, such as the
DC1366.
The LTC4269IDKD-1 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-1 con-
trols a high-power, small-sized power supply that
utilizes a highly-efficient isolated flyback topology
with synchronous rectification. The DC1335A-B sup-
plies a 5V output at up to 5A.
DC1335A-B 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
5.0V ± 1%
Maximum Output Current
V
PORT
= 42V
4.5A
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
±0.4% (typ)
Peak to Peak Deviation with Load Step of 2.5A to 5A
±240mV (< ±5%) (typ)
Load Transient Response
Settling Time (within 1% of V
OUT
)
< 100us (typ)
Switching Frequency
250kHz (typ)
Efficiency
VPORT = 50V, IOUT = 4A, not incl. diode bridge
91% (typ)
OPERATING PRINCIPLES
A compatible high power PSE board, such as the
DC1366, is connected to the DC1335A-B at the RJ45
connector J1 (see the schematic). As required by
IEEE802.3at, a diode bridge is used across the data
pairs and signal pairs. Schottky diodes (D2-9) are
used at the input to improve efficiency over standard
diode bridges. The LTC4269IDKD-1 provides an
IEEE802.3at standard PoE 25k signature resistance
and is set for a power class 4. When the PD is pow-
ered and voltage is above the PoE ‘‘On Voltage’’, the
