2
AFBR-0978Z Circuit Design
The evaluation board (Figure 1) is based on the reference
design for the AFBR-5978Z transceiver (see application
note 5289).
The data signal from the twisted pair medium is routed
through magnetics to the media converter IC ML6652
input pins (TPINP and TPINN); a 100 W resistor provides the
termination. The transmitter outputs of the ML6652 (IOUT
and IOUT#) are directly connected, over a 50 W transmis-
sion line, to the input of the transceiver with a pull-up
resistor of 75 W to Vcc, which is placed close to the trans-
ceiver. No external capacitor is required since the TD and
TD inputs of the transceiver are internally AC coupled.
The data signal is routed over a 50 W transmission line
from the transceiver RD and RD outputs to the input pins
of the ML6652 (FOINP and FOINN). These LVPECL inputs
are internally biased and need to be AC coupled. The
AFBR-5978Z datasheet states in the functional I/O section
that when AC coupling is used, the LVPECL outputs of
the transceiver have to be pulled to ground before the
AC coupling to DC bias the output. This is achieved by
use of a bias resistor of 160 W. The twisted pair outputs
of the ML6652 (TPOUTP and TPOUTN) are a differential
current output pair that drives the data signal through the
magnetics into the twisted pair medium. Both outputs are
pulled up to Vcc by a 50 W resistor.
Board Power
The supplied 5 V power adapter is connected to the
board by a DC plug and is suitable for 220 V/50 Hz or
110 V/60 Hz outlets. Note that this power adapter does
not ground the board to earth. To avoid damage to mea-
surement equipment connected to the board or incorrect
measurement results, make sure the evaluation board is
connected to ground. Connecting one of the I/O ground
pins or the DC plug ground pin to earth accomplishes
this.
Initial Setup
The twisted pair interface (RJ-45 port) is conFigured in
a straight-through mode. If the evaluation kit is used to
link two Ethernet devices, one of these devices should be
a hub or switch. Otherwise one cross-over cable needs to
be used to complete the link.
To get started it is recommended to set-up both AFBR-
0978Z boards in the “transparent with auto-negotiation”
mode. This is established by setting S2: 1-OFF, 2-OFF,
3-OFF, 4-ON and setting S3: all OFF. See table 1 for other
settings.
Once the hardware configuration has been set, the AFBR-
0978Z evaluation board is ready to be incorporated in the
Ethernet (test) environment.
Table 1. Function descriptions and switch settings for DIP switches S2 and S3
S2 Function Switch State
Twisted Pair output ON 1 OFF
Twisted Pair output OFF 1 ON
Fiber Optic output ON 2 OFF
Fiber Optic output OFF 2 ON
Link Integrity Warning mode enabled
(works only if media converter is set in
Forced 10 or 100 Mbps mode)
3
4
ON
OFF
Link Integrity Warning mode disabled
(default)
3
4
OFF
ON
S3 Function Switch State
Forced 10 Mbps mode
(auto-negotiation is off, duplex mode is
selected by link partners)
1
2
3
4
OFF
ON
OFF
OFF
Forced 100 Mbps mode
(auto-negotiation is off, duplex mode is
selected by link partners)
1
2
3
4
ON
OFF
OFF
OFF
Non-transparent half duplex auto-
negotiation
(for FO partner without auto-negotiation,
only half duplex is advertised)
1
2
3
4
OFF
OFF
ON
OFF
Non-transparent auto-negotiation
(for FO partner without auto-negotiation)
1
2
3
4
OFF
OFF
OFF
ON
Transparent with auto-negotiation
(suitable when both FO and TP partners
support auto-negotiation)
1
2
3
4
OFF
OFF
OFF
OFF