LTC4265 LINER [Linear Technology], LTC4265 Datasheet - Page 16

• Manufacturer Part Number: LTC4265
• Description: IEEE 802.3at High Power PD Interface Controller with 2-Event Classifi cation Recognition
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
LTC4265
Shutdown Interface
To corrupt the signature resistance, the SHDN pin can be
driven high with respect to V
unused, connect SHDN directly to V
Exposed Pad
The LTC4265 uses a thermally enhanced DFN12 package
that includes an Exposed Pad. The exposed may be elec-
trically connected to V
circuit board heat sink.
Auxiliary Power Source
In some applications, it is desirable to power the PD from
an auxiliary power source such as a wall adapter.
Auxiliary power can be injected into an LTC4265-based PD
at the input of the LTC4265, the output of the LTC4265, or
even the output of the DC/DC converter. In addition, some
PD application may desire auxiliary supply dominance
or may be confi gured for PoE dominance. Furthermore,
16
RJ45
1
2
3
6
4
5
7
8
TX
TX
RX
RX
IN
+
–
+
–
SPARE
SPARE
and must connect to a printed
+
–
IN
TRANSFORMER
ISOLATED
or connected to GND. If
WALL
T1
IN
Figure 10. Auxiliary Power Dominant PD Interface
.
+
–
TO PHY
BR1
BR2
+
–
+
–
PD applications may also opt for a seamless transition
— that is, without power disruption — between PoE and
auxiliary power.
The most common auxiliary power option injects power
between the LTC4265 and the DC/DC converter. Figure 10
presents an example of this application.
In this example, the auxiliary port injects 48V onto the line
via diode D1. The components surrounding the SHDN pin
are selected so that the LTC4265 disconnects power to the
output when the auxiliary supply reaches 36V.
This confi guration is an auxiliary-dominant confi guration.
That is, the auxiliary power source supplies the power even
if PoE power is already present. This confi guration also
provides a seamless transition from PoE to auxiliary power
when auxiliary power is applied, however, the removal of
auxiliary power to PoE power is not seamless.
Contact Linear Technology applications support for detail
information on implementing a custom auxiliary power
supply.
TVS
100k
10k
10k
36V
0.1μF
100V
SHDN
V
IN
LTC4265
V
GND
OUT
D1
4265 F10
C1
LOAD
PD
4265f