Application Notes

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16

15

14

1

2

3

TX1+

TX1–

TXCT

TD+

TD-

TCT

11

10

9

6

7

8

RX1+

RX1–

RXCT

RD+

RD-

RCT

5

4

12

13

N/C

N/C

1:1

1:1

PoE Interface Transformer

H2019 (Pulse Engineering)

J1

RJ-45

Ethernet

Connection

from PSE

PD

Circuitry

N/C

N/C

PTB48540B

10

Data Line B

9

Spare Line A

4

Spare Line B

8

Input Ref

7

A - Detect - B

A - Class - B

Output Inhibit

Data Line A

+V

OUT

V

–V

OUT

3

2

1

5612

11

13

+3.3 V

0 V

L1

T1

T2

1

2

3

4

5

6

7

8

Figure 4-1; Power-Over-Ethernet Application Schematic

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

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.

Not Recommended for New Designs