Evaluates: MAX3286/MAX3296
MAX3296 Longwave (Common Anode)
Evaluation Kit
_______________________________________________________________________________________
3
turn potentiometer). This sets the regulation point
for the photodiode current to 1.7V / 50k
Ω
= 34µA.
The resulting laser bias current depends upon the
relationship between laser power and photodiode
output current.
WARNING:
Consult your laser data
sheet to ensure that 34µA of photodiode monitor
current does not correspond to excessive laser
power.
6) Set potentiometer R8 (R
MOD
) to maximum resis-
tance by turning the screw counterclockwise until a
faint click is felt (30 full revolutions in the 0
Ω
to
50k
Ω
range of the multiturn potentiometer). This
minimizes the modulation current (AC drive applied
to laser).
7) Set potentiometer R7 (R
TC
) to maximum resistance
by turning the screw counterclockwise until a faint
click is felt (30 full revolutions in the 0
Ω
to 100k
Ω
range of the multiturn potentiometer). This mini-
mizes the tempco of the modulation current.
8) Attach a 50
Ω
SMA terminator to J6 to match the
laser loading.
9) Place jumpers across JU7 (EN), JU8 (
EN
), and JU9
(PORDLY).
10) If you intend to power the board from a +5V supply,
place a jumper across JU6 (LV). Do not apply
power yet.
11) Make sure there is no jumper on JU10 (FLTDLY).
This enables the safety circuitry.
12) Attach differential sources to SMA connectors J3
and J4. Each source should have a peak-to-peak
amplitude between 100mV and 830mV.
13) Apply 3.3V or +5V power to the board at the
J9 (VCC) and J10 (GND) test points.
14) While monitoring the laser output, adjust R14 (R
SET
)
until the desired laser bias current is obtained.
Turning the R14 potentiometer screw counterclock-
wise increases the laser bias current.
15) While monitoring the laser output, adjust R8 (R
MOD
)
until the desired laser modulation current is
obtained. Turning the R8 potentiometer screw
clockwise increases the laser modulation current.
COMPONENT
NAME
FUNCTION
D4
Fault
The LED shines red when a fault has occurred. The fault condition can be cleared by
removing, then reinstalling, jumpers at JU7 or JU8.
JU6
LV
Placing a jumper on JU6 connects the LV pin to ground and programs the power-on
reset circuit for +4.5V to +5.5V operation.
JU7
EN
Placing a jumper on JU7 ties the EN pin to VCC. When JU7 is not installed, the EN pin
is pulled low by its internal pull-down.
JU8
EN
Placing a jumper on JU8 ties the
EN
pin to ground. When JU8 is not installed, the
EN
pin is pulled high by its internal pull-up.
JU9
PORDLY
Placing a jumper on JU9 connects the PORDLY pin to a 0.01µF capacitor (C6). Leaving
JU9 open floats the PORDLY pin and minimizes the power-on reset time.
JU10
FLTDLY
Placing a jumper on JU10 disables the laser-driver safety features.
R7
R
TC
Potentiometer R7, in conjunction with potentiometer R8 (R
MOD
), sets the tempco of
the laser modulation current. Turn the potentiometer screw counterclockwise to
increase the resistance. The tempco decreases when the potentiometer screw turns
counterclockwise.
R8
R
MOD
Potentiometer R8, in conjunction with potentiometer R7 (R
TC
), sets the peak-to-peak
amplitude of the laser modulation current. Turn the potentiometer screw counterclock-
wise to increase the resistance. The laser modulation current amplitude decreases
when the potentiometer screw turns counterclockwise.
R14
R
SET
Potentiometer R14 adjusts the desired laser DC-current bias point. Potentiometer R14
sets the resistance from MD to ground. MD regulates to 1.7V. Turn the potentiometer
screw clockwise to increase the resistance. The total range is 0 to 100k
Ω
. The laser’s
average power increases when the potentiometer screw turns counterclockwise.
SP1, SP2
—
Short across these shunts with a bridge of solder when performing electrical
evaluation.
Table 1. Adjustment and Control Descriptions