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LTC4264
15
4264f
thermal shutdown. For DC loads the maximum ambient
temperature can be calculated as:
TMAX = 125 – θJA PWR (°C)
where TMAX is the maximum ambient operating tempera-
ture,
θJA is the junction-to-ambient thermal resistance
(43°C/W), and PWR is the power dissipation for the
LTC4264 in Watts (IPD
2RON).
EXTERNAL INTERFACE AND COMPONENT SELECTION
Transformer
Nodes on an Ethernet network commonly interface to
the outside world via an isolation transformer (Figure 9).
For powered devices, the isolation transformer must
include a center tap on the media (cable) side. Proper
termination is required around the transformer to provide
correct impedance matching and to avoid radiated and
conducted emissions. For high power applications beyond
IEEE 802.3af limits, the increased current levels increase
the current imbalance in the magnetics. This imbalance
reduces the perceived inductance and can interfere with
data transmission. Transformers specically designed for
high current applications are required. Transformer vendors
such as Bel Fuse, Coilcraft, Halo, Pulse, and Tyco (Table 4)
can provide assistance with selection of an appropriate
isolation transformer and proper termination methods.
These vendors have transformers specically designed
for use in high power PD applications.
16
14
15
1
3
2
RX –
6
RX +
3
TX –
2
TX +
RJ45
T1
PULSE H2019
4264 F09
1
7
8
5
4
11
9
10
6
8
7
D3
SMAJ58A
TVS
BR1
HD01
BR2
HD01
TO PHY
GND
LTC4264
C1
VIN
VOUT
SPARE –
SPARE+
C14
0.1
F
100V
Figure 9. PD Front-End with Isolation Transformer, Diode Bridges, Capacitors and TVS
APPLICATIONS INFORMATION
Table 4. Power over Ethernet Transformer Vendors
VENDOR
CONTACT INFORMATION
Bel Fuse Inc.
206 Van Vorst Street
Jersey City, NJ 07302
Tel: 201-432-0463
www.belfuse.com
Coilcraft Inc.
1102 Silver Lake Road
Gary, IL 60013
Tel: 847-639-6400
www.coilcraft.com
Halo Electronics
1861 Landings Drive
Mountain View, CA 94043
Tel: 650-903-3800
www.haloelectronics.com
Pulse Engineering
12220 World Trade Drive
San Diego, CA 92128
Tel: 858-674-8100
www.pulseeng.com
Tyco Electronics
308 Constitution Drive
Menlo Park, CA 94025-1164
Tel: 800-227-7040
www.circuitprotection.com