Datasheet
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1249
POE TO 3.3V@3.0A ISOLATED
1
LTC4267CDHC-3
DESCRIPTION
Demonstration circuit 1249 is a PoE to 3.3V@3.0A
Isolated Converter featuring the LTC4267CDHC-3.
The board provides a complete IEEE 802.3af
power device (PD) interface and isolated 3.3V
power supply solution for use in Power-over-
Ethernet (PoE) applications in a very small printed
circuit board footprint.
The LTC4267-3 integrates the 25k
Ω
signature re-
sistor, classification current source, thermal over-
load protection, signature disable and power good
signal along with an undervoltage lockout opti-
mized for use with the IEEE required diode bridge.
The precision dual level input current limit allows
the LTC4267-3 to charge load capacitors and in-
terface with legacy PoE systems.
The LTC4267-3 combines the above features with
a current mode switching controller designed for
driving a N-channel MOSFET. It features pro-
grammable 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.
Table 1. Performance Summary (T
A
= 25°C)
PARAMETER CONDITION VALUE
Turn-on Voltage Input from PSE -37V
Maximum Turn-off Voltage Input from PSE, PD switch turns off -31V
Minimum operating voltage I
OUT
= 3A -33V
Power Converter Input operating range V
OUT
= 3.3V, I
OUT
= 0 to 3.0A -37V to -57V
Maximum Input Current Input from PSE, PD high level current limit 375mA, typical
Maximum Output Current V
OUT
= 3.3V 3.0A
Output Voltage V
IN
= 48VDC from PSE, I
OUT
= 3.0A 3.3V, typical
Line (0% to 100% full load) 2%
Output Regulation
Load (0% to 100% of rated full load) 2%
QUICK START PROCEDURE
Demonstration circuit 1249 is easy to set up to
evaluate the performance of the LTC4267-3. For
proper equipment setup, refer to figure 1 and fol-
low the procedure below:
1. With the power source to the PSE turned off,
connect the input power supply to the board
through the J1 filtered Ethernet connector.
2. In addition to a PSE, the DC1249 board can
be powered by an alternate input power supply