LTC4269CDKD-2#TRPBF Linear Technology, LTC4269CDKD-2#TRPBF Datasheet - Page 18

• Manufacturer Part Number: LTC4269CDKD-2#TRPBF
• Description: IC PD/SYNC FORWARD CTRLR 32-DFN
• Manufacturer: Linear Technology
• Type: Power Over Ethernet (PoE)r

Specifications of LTC4269CDKD-2#TRPBF

• Applications: Power Interface Switch for Power Over Ethernet (PoE) Devices
• Voltage - Supply: 14 V ~ 16 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 32-DFN
• Current - Supply: 1.35mA
• Interface: IEEE 802.3af
• Controller Type: Powered Device Interface Controller (PD)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

LTC4269-2
applicaTions inForMaTion
THERMAL PROTECTION
The IEEE 802.3af/at specification requires a PD to withstand
any applied voltage from 0V to 57V indefinitely. However,
there are several possible scenarios where a PD may
encounter excessive heating.
During classification, excessive heating may occur if the
PSE exceeds the 75ms probing time limit. At turn-on, when
the load capacitor begins to charge, the instantaneous
power dissipated by the PD interface can be large before
it reaches the line voltage. And if the PD experiences a
fast input positive voltage step in its operational mode
(for example, from 37V to 57V), the instantaneous power
dissipated by the PD Interface can be large.
The LTC4269-2 includes a thermal protection feature which
protects the LTC4269-2 from excessive heating. If the
LTC4269-2 junction temperature exceeds the overtempera-
ture threshold, the LTC4269-2 discontinues PD operations.
Normal operation resumes when the junction temperature
falls below the overtemperature threshold and when C1 is
charged up and power good becomes inactive.
EXTERNAL INTERFACE AND COMPONENT SELECTION
Transformer
Nodes on an Ethernet network commonly interface to the
outside world via an isolation transformer. For PDs, the
isolation transformer must also include a center tap on
the RJ45 connector side (see Figure 7).
RJ45

1
2
3
6
4
5
7
8
Figure 7. PD Front End with Isolation Transformer, Diode
Bridges, Capacitors and a Transient Voltage Suppressor (TVS)
TX
TX
RX
RX
+
–
+
–
SPARE
SPARE
COILCRAFT ETH1-230LD
+
–
14
12
13
10
11
9
T1
1
3
2
5
4
6
BR2
HD01
TO PHY
C14
0.1µF
100V
SMAJ58A
TVS
D3
BR1
HD01
V
PORTN
LTC4269-2
V
PORTP
V
42692 F07
NEG
C1
The increased current levels in a Type 2 PD over a Type 1
increase the current imbalance in the magnetics which
can interfere with data transmission. In addition, proper
termination is also required around the transformer to
provide correct impedance matching and to avoid radiated
and conducted emissions. Transformer vendors such as
Bel Fuse, Coilcraft, Halo, Pulse and Tyco (Table 4) can
assist in selecting an appropriate isolation transformer
and proper termination methods.
Table 4. Power over Ethernet Transformer Vendors
VENDOR
Bel Fuse Inc.
Coilcraft Inc.
Halo Electronics
PCA Electronics
Pulse Engineering
Tyco Electronics
Input Diode Bridge
Figure 2 shows how two diode bridges are typically con-
nected in a PD application. One bridge is dedicated to the
data pair while the other bridge is dedicated to the spare
pair. The LTC4269-2 supports the use of either silicon or
Schottky input diode bridges. However, there are trade-offs
in the choice of diode bridges.
An input diode bridge must be rated above the maximum
current the PD application will encounter at the tempera-
ture the PD will operate. Diode bridge vendors typically
call out the operating current at room temperature, but
derate the maximum current with increasing temperature.
Consult the diode bridge vendors for the operating current
de-rating curve.
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
16799 Schoenborn Street
North Hills, CA 91343
Tel: [phone]
www.pca.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
42692fb