PTB48540 Datasheet, PDF (9/12 Pages) Texas Instruments – 10-W Power-Over-Ethernet Isolated Power Module Assembly

Application Notes
PTB48540 Series
Using the PTB48540 Series Module in a
Power-Over-Ethernet (PoE) Application
The schematic of Figure 4-1 shows an example of how a
PTB48540 module may be connected to a PoE compliant
system. The connector J1 is the input from the PoE source.
In a Power-over-Ethernet (PoE) application, the power
and high-frequency data signals share the same conductors
in the Ethernet cable. The data and power signals must
be separated using an IEEE 802.3af compliant PoE mag-
netic module.
The magnetic module incorporates the customary isola-
tion transformers, T1 and T2. The transformers each
include a center tap, across which the dc current from the
Ethernet power source equipment (PSE) is conveniently
extracted. The transmit and receive hf Ethernet data
Figure 4-1; Power-Over-Ethernet Application Schematic
appear as differential signals to each transformer. These
signals are isolated by the transformers, allowing the
Ethernet communication content to flow freely between
the connector and the powered device (PD) circuitry.
The common-mode inductor, L1, is a popular addition
to off-the-shelf PoE magnetic modules. The inductor
provides additional rejection to common mode noise
currents, which may otherwise be present on either the
data or power signals.
The PTB48540 module complies with the PoE protocols,
provides the required isolation, and converts the raw
power from the PSE to a precision regulated 3.3-VDC
power source for the remote PD circuitry.
J1
RJ-45
Ethernet
Connection
from PSE
1
2
3
4
5
6
7
8
PoE Interface Transformer
H2019 (Pulse Engineering)
16 _TX1+
T1
TD+ ¹
15 _TXCT
L1
14 TX1–
13
N/C
12
N/C
11 _RX1+
TCT ²
TD- ³
1:1
4
N/C
5
N/C
T2
RD+ ⁶
10 _RXCT
RCT ⁷
9 _RX1–
RD- ⁸
1:1
5
6
A - Detect - B
12
11
A - Class - B
10
Data Line A
9
Data Line B
4
Input Ref
PTB48540B
8
Spare Line A
7
Spare Line B
3
+V_OUT
2
V_OUT Adj
1
–V_OUT
Output Inhibit
13
PD
Circuitry
+3.3 V
0V
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