2) Remove the shunt from JU5 to enable the outputs.
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.
3) Adjust R41, the MOD potentiometer, for 10kΩ resis-
tance between pins 1 and 3 (test point 3 and
ground).
4) Adjust R42, the BIAS potentiometer, for 10kΩ resis-
tance between pins 1 and 3 (test point 2 and
ground).
5) Adjust R40, the APC potentiometer, for 10kΩ resis-
tance between pins 1 and 3 (test point 8 and ground).
6) Apply a differential input signal (max amplitude
≤800mV per side) to J7 and J8 (DATA+ and DATA-).
7) If the latch is enabled, apply a differential clock sig-
nal (max amplitude ≤800mV per side) to J5 and J6
(CLK+ and CLK-).
8) Attach a high-speed oscilloscope with 50Ω inputs
to J9.
9) Power up the board with a +3.3V supply.
10) Adjust R42 until the desired laser bias current is
achieved.
11) Adjust R41 until the desired laser modulation cur-
rent is achieved.
Optical Evaluation
For optical evaluation of the MAX3869, configure the
evaluation kit as follows:
1) If data is to be latched, remove the shunt from JU1
to enable the input clock; otherwise, leave the shunt
in place.
2) Remove the shunt from JU2 to enable the outputs.
3) The EV kit is designed to allow connection of a vari-
ety of possible laser/monitor diode pin configura-
tions. 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
).
• 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. Three of these
pads (the middle and outside positions) are initially
not connected. The other two pads are connected
to V
CC
. Solder the anode and cathode of the moni-
tor photodiode to any two of the three pads that are
not connected. Then connect the anode to the MD
pin by shorting the corresponding solder jumper
(Figure 1). Connect the cathode to V
CC
by using
solder to bridge to an adjacent V
CC
pad.
Note: When performing resistance checks, manual-
ly set the ohmmeter to a high range to avoid for
ward biasing the on-chip ESD protection diodes.
4) Adjust R14, the MOD potentiometer, for maximum
resistance between pins 1 and 3 (test point 5 and
ground).
5) Adjust R15, the BIAS potentiometer, for maximum
resistance between pins 1 and 3 (test point 4 and
ground).
6) Adjust R16, the APC potentiometer, for desired opti-
cal power. (Refer to the Design Procedure section
of the MAX3869 data sheet.)
7) Apply a differential input signal (≤800mV per side)
to J1 and J2 (DATA+ and DATA-).
8) Apply a differential clock signal (≤800mV per side)
to J3 and J4 (CLK+ and CLK-).
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 R15 until the LED, D1, is no longer illuminat-
ed. Optical power can be observed on an oscillo-
scope connected to an optical/electrical converter.
12) Adjust R14 until the desired optical amplitude is
achieved. Optical amplitude can be observed on
an oscilloscope connected to an optical/electrical
converter.
