ltc4268cdkd-1-trpbf Linear Technology Corporation, ltc4268cdkd-1-trpbf Datasheet - Page 22

• Manufacturer Part Number: ltc4268cdkd-1-trpbf
• Description: High Power Pd With Synchronous Noopto Flyback Controller
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
nuisance trips of the thermal shutdown, it may be necessary
to limit the maximum ambient temperature. Limiting the
die temperature to 125°C will keep the LTC4268-1 from
hitting thermal shutdown. For DC loads the maximum
ambient temperature can be calculated as:
where T
ture, θ
(49°C/W), and PWR is the power dissipation for the
LTC4268-1 in Watts (I
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
LTC4268-1
22
T
MAX
JA
MAX
= 125 – θ
is the junction-to-ambient thermal resistance
is the maximum ambient operating tempera-
JA
• PWR (°C)
PD
RJ45
1
2
3
6
4
5
7
8
Figure 9. PD Front-End Isolation Transformer, Diode Bridges, Capacitors and TVS
2
TX
TX
RX
RX
• R
+
–
+
–
SPARE
SPARE
ON
).
+
–
PULSE H2019
16
15
14
11
10
9
T1
1
2
3
6
7
8
BR2
HD01
TO PHY
C14
0.1μF
100V
reduces the perceived inductance and can interfere with
data transmission. Transformers specifi cally 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
Table 4. Power over Ethernet Transformer Vendors
VENDOR
Bel Fuse Inc.
Coilcraft Inc.
Halo Electronics
Pulse Engineering
Tyco Electronics
SMAJ58A
BR1
HD01
TVS
D3
V
PORTN
LTC4268-1
V
PORTP
V
42681 F09
NEG
+
CONTACT INFORMATION
206 Van Vorst Street
Jersey City, NJ 07302
Tel: [phone]
www.belfuse.com
1102 Silver Lake Road
Gary, IL 60013
Tel: [phone]
www.coilcraft.com
1861 Landings Drive
Mountain View, CA 94043
Tel: [phone]
www.haloelectronics.com
12220 World Trade Drive
San Diego, CA 92128
Tel: [phone]
www.pulseeng.com
308 Constitution Drive
Menlo Park, CA 94025-1164
Tel: [phone]
www.circuitprotection.com
C1
V
IN
42681fa