Evaluates: MAX3863
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MAX3863 Evaluation Kit
Optical Evaluation
1) If the data is latched, place the shunt for JU2 to
ground RTEN to enable the clock input. Otherwise,
set JU2 so that RTEN is connected to V
CC
.
2) To enable the part, set shunt JU1 so that EN is
grounded.
3) To disable the APC loop, install JU15. This allows
direct control of the bias current.
4) To eliminate interaction between the bias current
and the modulation current, remove JU3.
5) The EV kit is designed to allow connection of various
laser/monitor diode pin configurations. Connect a
TO-header style laser with monitor diode (Figure 1)
as follows:
• Keeping the module leads as short as possible,
connect the laser diode cathode to the center
pad on the component side of the circuit board.
Connect the anode to one of the two remaining
VCC pads, such that the monitor diodes leads
can solder to the bottom of the circuit board.
• The monitor photodiode pads are arranged in a
series of five pads on the bottom (solder side) of
the PC board. Next to the five photodiode pads
are three solder bridge pad pairs. The MD pin
can be connected to any three of the five pads
through a solder bridge. The remaining two of
the five pads are connected to VCC. The VCC
pads are placed between the pads going to the
solder bridge pads. Solder the photodiode to
the nearest two of the three pads going to the
solder bridge pads (Figure 1).
• Connect the anode of the photo diode to the MD
pin by adding a solder bridge to one of the three
solder bridge positions. Connect the photodiode
cathode to VCC by bridging the cathode pad to
the adjacent VCC pad.
Note: When performing the following resistance
checks, manually set the ohmmeter to a high
range to avoid forward biasing the on-chip ESD
protection diodes.
6) Adjust R16, the MODSET potentiometer, for maxi-
mum resistance between test point 3 and ground.
7) Adjust R14, the BIASMAX potentiometer, to give a
bias current larger than the threshold current speci-
fied for the laser diode. A combined resistance
value of 5.9kΩ gives approximately 40mA of bias
current:
8) Apply a differential input signal of 250mV
P-P
to the
DATA inputs, and to the CLK inputs if retiming is
enabled.
9) Attach the laser diode fiber connector to an opti-
cal/electrical converter.
10) Power up the board with a +3.3V supply.
11) Adjust R16 until the desired optical amplitude is
achieved. Optical amplitude can be observed on an
oscilloscope connected to an optical/electrical con-
verter. If the signal clips, the bias current might
need to be increased. Refer to the Design
Procedure section of the MAX3863 data sheet to set
the modulation compensation factor.
