MAX3737 Evaluation Kit
4 _________________________________________________________________________________________
Evaluates: MAX3737
Optical Evaluation
For optical evaluation of the MAX3737, configure the
evaluation kit as follows:
1) Remove shunt JU16 to use the filter inductor.
2) If the EV kit is to be used without the optional
shutdown transistor (Q4), place a shunt on JU20.
3) To enable the outputs, connect TX_DISABLE to GND
by placing a shunt on JU30.
4) The EV kit is designed to allow connection of a
variety of possible laser/monitor diode pin
configurations. Connect a TO-header style laser with
monitor diode (Figure 1) as follows:
• Keeping its leads as short as possible, connect
the laser diode to two of the three pads in the
cutout portion on the top (component) side of the
PC board. Solder the laser diode cathode to the
center pad, and solder the anode to either of the
other two pads (they are both connected to V
CC
through the shutdown transistor (Q4)).
• Connect the monitor photodiode to two of the
five pads on the bottom (solder) side of the PC
board, directly below the laser diode pads.
Connect the anode and cathode of the
photodiode as shown in figure 1.
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.
1) Adjust R57, the R
MODSET
potentiometer, for maximum
resistance (≈50kΩ) between TP19 and ground. This
sets the modulation current to a low value (<10mA).
(Refer to the Design Procedure section of the
MAX3737 data sheet.)
6) Adjust R55, the R
APCSET
potentiometer, for maximum
resistance (≈50kΩ) between TP20 and ground. This
sets the photodiode current to a low value (<18µA).
(Refer to the Design Procedure section of the
MAX3737 data sheet.)
WARNING: Consult your laser data sheet to ensure
that 18µA of photodiode current and 10mA of
modulation current does not correspond to excessive
laser power.
7) Install R67, the R
PC_MON
resistor, to set the maximum
monitor diode current (I
MDMAX
, see below).
MDMAX
REF
PC_MON
I
V
R =
8) Install R64, the R
BC_MON
resistor, to set the maximum
bias current (I
BIASMAX
, see below).
BIASMAX
REF
BC_MON
I
V08
R
×
=
9) Install R63, the R
MC_MON
resistor, to set the maximum
modulation current (I
MODMAX
, see below).
MODMAX
REF
MC_MON
I
V862
R
×
=
10) Apply a differential input signal (200mV
P-P
to
2400mV
P-P
) between SMA connectors J5 and J4 (IN+
and IN-).
11) Attach the laser diode fiber connector to an
optical/electrical converter.
12) Connect a +3.3V supply between J3 (V
CC
) and J6
(GND). Adjust the power supply until the voltage
between TP15 and ground is +3.3V.
13) Adjust R55 (R
APCSET
) until the desired average optical
power is achieved.
14) The MD, MOD and BIAS currents can be monitored
at TP28 (V
PC_MON
) and TP27 (V
BC_MON
) and TP26
(V
MC_MON
) using the equations below:
PC_MON
PC_MON
MD
R
V
I =
BC_MON
BC_MON
BIAS
R
V08
I
×
=
MC_MON
MC_MON
MOD
R
V268
I
×
=
Note: If the voltage at TP26, TP27 or TP28 exceeds
1.38V, the TX_FAULT signal will be asserted and
latched.
15) Adjust R57 (R
MODSET
) until the desired optical
amplitude is achieved. Optical amplitude can be
observed on an oscilloscope connected to an
optical/electrical converter. Laser overshoot and
ringing can be improved by appropriate selection of
R39 and C24, as described in the Design Procedure
section of the MAX3737 data sheet.
