QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 859
MULTIPLE OUTPUT PD
1
LTC4267
DESCRIPTION
Demonstration circuit 859 is a Multiple Output PD fea-
turing the LTC4267. The board provides a complete
IEEE 802.3af power device (PD) interface and isolated
power supply solution for use in Power over Ethernet
(PoE) applications. It generates 1.8V @ 2.5A, 2.5V @
1.5A and 3.3V @ 0.5A.
The LTC4267 integrates the 25k
Ω
signature resistor,
classification current source, thermal overload protec-
tion, signature disable and power good signal along with
an undervoltage lockout optimized for use with the IEEE
required diode bridge. The precision dual level input
current limit allows the LTC4267 to charge load capaci-
tors and interface with legacy PoE systems.
The LTC4267 combines the above features with a cur-
rent mode switching controller designed for driving a 6V
rated N-channel MOSFET. It features programmable
slope compensation, soft-start, and constant frequency
operation, minimizing electrical noise even with light
loads.
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
Turn-on Voltage
Input from PSE
-36V maximum
Maximum Turn-off Voltage
Input from PSE, PD switch turns off
-32V
Power Converter Input operating range
V
OUT
=3.3V, I
OUT
= 0 to 2.6A
-37V to -57V
Maximum Input Current
Input from PSE, PD high level current limit
375 mA, typical
Maximum Output Current
V
OUT1
=1.8V
V
OUT2
=2.5V
V
OUT3
=3.3V
2.5A
1.5A
0.5A
Output Voltage
V
IN
=48VDC from PSE
1.79V, typical
2.5V, typical
3.3V, typical
Output Regulation
V
OUT1
= 1.8V, V
IN
= -37 to -57VDC, zero to full load
V
OUT2
= 2.5V, V
IN
= -37 to -57VDC, zero to full load
V
OUT3
= 3.3V, V
IN
= -37 to -57VDC, zero to full load
+ 5%
+ 2%
+ 5%
