19-1644; Rev 1; 6/00
MAX3296 Shortwave or VCSEL
(Common Cathode) Evaluation Kit
General Description
The MAX3296 shortwave or vertical cavity-surface emit-
ting laser (VCSEL) evaluation kit (EV kit) is an assem-
bled, surface-mount demonstration board that allows
easy optical and electrical evaluation of the MAX3286
1.25Gbps laser driver or the MAX3296 2.5Gbps laser
driver in the common-cathode configuration. Short-
wavelength laser diodes (wavelength
≤
980nm) and
VCSELs typically require a common-cathode configura-
tion. In the common-cathode configuration, the laser’s
cathode connects to ground and the laser is driven at
its anode.
The MAX3296 shortwave or VCSEL EV kit regulates the
laser bias current to keep a constant photodiode cur-
rent or the kit directly senses the laser bias current and
holds it constant.
Refer to the MAX3296EVKIT-LW for evaluation of the
MAX3286/MAX3296 with long-wavelength laser diodes
in the common-anode configuration.
o
Drives Common-Cathode Lasers
o
Includes Socket for Laser Insertion
o
LED Fault Indicator
o
Evaluates Either MAX3286 or MAX3296 (installed)
o
Adjustable DC Bias Current for VCSELs
o
Adjustable Photodiode Current
o
Adjustable Modulation Current
o
Adjustable Modulation Current Tempco
o
Configured for Electrical Operation, No Laser
Necessary
Features
Evaluates: MAX3286/MAX3296
Ordering Information
PART
MAX3296EVKIT-SW
MAX3296CGISEVKIT
TEMP. RANGE
0°C to +70°C
0°C to +70°C
IC PACKAGE
32 TQFP
28 QFN
Component List
DESIGNATION QTY
C1–C5, C13,
C14, C22, C25,
C26
C11
C12
C23
D1
D3
J1, J2, J5
10
DESCRIPTION
0.01µF ±10%, 16V min, X7R ceramic
capacitors (0402)
0.1µF ±10%, 16V min, X7R ceramic
capacitor (0402)
Open, user supplied (0402)*
10µF ±10%, 16V tantalum capacitor
AVX TAJC106K016
Open, user supplied (laser diode and
photodiode assembly; see Figure 1)
Red LED
SMA connectors (edge mount)
EFJohnson 142-0701-801 or
Digi-Key J502-ND
Test points
Digi-Key 5000K-ND
2-pin headers (0.1in centers)
Digi-Key S1012-36-ND
Ferrite beads
Murata BLM11HA102SG
Ferrite bead
Murata BLM11HA601SG
R5
R9, R30
R10
R11
R12
R13
R20
R22
1
2
1
1
1
1
1
1
DESIGNATION QTY
L8
Q1
1
0
1
0
1
3
Q2
Q4
R2
R3
R4
1
0
1
1
1
1
1
DESCRIPTION
Ferrite bead (included but not installed)
Murata BLM11HA102SG
Open
Zetex FMMT491A
Zetex FMMT591A
115Ω ±1% resistor (0402)
100kΩ variable resistor
Bourns or Digi-Key 3296W-104-ND
50kΩ variable resistor
Bourns or Digi-Key 3296W-503-ND
10kΩ variable resistor
Bourns or Digi-Key 3296W-103-ND
1kΩ ±5% resistors (0402)
5.1kΩ ±5% resistor (0402)
200Ω variable resistor
Bourns or Digi-Key 3296W-201-ND
0Ω resistor (0402)
24.9Ω ±1% resistor (0402)*
49.9Ω ±1% resistor (0402)
36Ω ±5% resistor (0603)
J7, J8
JU1–JU5
L1, L2
L4
2
5
2
1
Component List continues on next page.
*These components are part of the compensation network, which reduces overshoot and ringing. Parasitic series inductance introduces
a zero into the laser’s frequency response. R13 and C12 add a pole to cancel this zero. The optimal values depend upon the laser
used. Maxim recommends R13 = 24.9Ω and C12 = 2pF as a starting point.
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
MAX3296 Shortwave or VCSEL
(Common Cathode) Evaluation Kit
Evaluates: MAX3286/MAX3296
Component List (continued)
DESIGNATION QTY
R23
R24
R25
TP1, TP3, TP4,
TP9, TP10,
TP14, TP15,
TP19, TP20
U1**
U1**
U1**
U1**
U2
1
1
1
9
1
1
1
1
1
DESCRIPTION
0Ω resistor (0603)
24.9Ω ±1% resistor (0402)
511Ω ±1% resistor (0402)
Test points
Digi-Key 5000k-NO
MAX3296CHJ (32-pin TQFP)
MAX3286CHJ (32-pin TQFP, included
but not installed)
MAX3296CGI (28-pin QFN)
MAX3286CGI (28-pin QFN included
but not installed)
MAX4322EUK (5-pin SOT23)
SHUNT
SP3
SP4
SP5
SP6
SP7
SP8
SP9
SP10
SP11
STATUS
Open
Closed
Closed
Closed
Closed
Closed
Open
Open
Closed
Refer to the MAX3286/MAX3296 Common-Cathode
Laser with Photodiode application circuit in the
MAX3286–MAX3289/MAX3296–MAX3299 data sheet.
2) Make sure nothing is installed in the laser socket
(Figure 1).
3) Confirm that R24 is installed.
4) Make sure L8 is not installed.
5) Confirm that C12 is open. Without a laser installed, no
compensation network is necessary.
6) Set potentiometer R5 (R
SET
) to midscale by turning
the screw counterclockwise until a faint click is felt,
then clockwise for 15 full revolutions (30 full revolu-
tions in the 0Ω to 10kΩ range of the multiturn poten-
tiometer). This sets the regulation point for the simulat-
ed photodiode current to (2.65V - 1.7V) / 5kΩ =
190µA. The photodiode emulator circuit regulates the
DC bias current out of Q4 to 28
×
190µA
≅
5mA.
7) Set potentiometer R4 (R
MOD
) to maximum resistance
by turning the screw counterclockwise until a faint
click is felt (30 full revolutions in the 0Ω to 50kΩ range
of the multiturn potentiometer). This minimizes the
modulation current.
8) Set potentiometer R3 (R
TC
) to maximum resistance by
turning the screw counterclockwise until a faint click is
felt (30 full revolutions in the 0Ω to 100kΩ range of the
multiturn potentiometer). This minimizes the tempera-
ture coefficient (tempco) of the modulation current.
9) Set potentiometer R11 to 30Ω of resistance by turning
the screw clockwise until a faint click is felt, then coun-
terclockwise for five turns.
10) Place jumpers across JU2 (EN), JU3 (EN), and JU4
(PORDLY).
**The
MAX3296/MAX3286CHJ parts are included with the
MAX3296EVKIT-SW. The MAX3296/MAX3286CGI parts are
included with the MAX3296CGIS.
Evaluating the MAX3286
TQFP Package
The MAX3296EVKIT-SW board can easily be modified to
accommodate the MAX3286. Desolder and remove the
MAX3296 (the EV board ships with the MAX3296CHJ
installed), and replace it with the MAX3286CHJ (includ-
ed with the EV kit). No other circuit modifications are
necessary.
QFN Package
The MAX3296CGIS EV kit board can be modified to
accommodate the MAX3286. Using a hot plate and a
small heating block to localize the heat underneath the
part, desolder and remove the MAX3296 (the EV board
ships with the MAX3296CGI installed), and replace it
with the MAX3286CGI (included with the EV kit). No
other circuit modifications are necessary.
Electrical Quick Start
Electrical Quick Start with
Simulated Photodiode Feedback
1) Configure the board so that it will servo the DC bias
current, achieving a fixed photodiode current and
activating the photodiode emulator circuit. Set up
the following shunts:
2
_______________________________________________________________________________________
MAX3296 Shortwave or VCSEL
(Common Cathode) Evaluation Kit
11) If you intend to power the board from a +5V supply,
place a jumper across JU1 (LV).
Do not apply power
yet.
12) Make sure there is no jumper on JU5 (FLTDLY).
13) Attach a cable with 50Ω characteristic impedance
between the J5 SMA output connector and the input
of the oscilloscope. Make sure the oscilloscope input
is 50Ω terminated.
14) Attach differential sources to SMA connectors J1 and
J2. Each source should have a peak-to-peak ampli-
tude between 100mV and 830mV.
15) Apply either +3.3V or +5V power to the board at the
J7 (VCC) and J8 (GND) test points. Set the current
limit to 300mA.
16) While monitoring the voltage on TP19, adjust R5
(R
SET
) until the desired DC bias current is obtained.
Turning the R5 potentiometer screw clockwise
increases the DC bias current.
17) While monitoring the J5 SMA connector output on the
oscilloscope, adjust R4 (R
MOD
) until the desired mod-
ulation current is obtained. Turning the R4 poten-
tiometer screw clockwise increases the modulation
current.
3) Confirm that R24 is installed.
4) Make sure L8 is not installed.
5) Confirm that C12 is open. Without a laser installed,
no compensation network is necessary.
6) Set potentiometer R11 to midscale by turning the
screw counterclockwise until a faint click is felt,
then clockwise for 15 full revolutions (30 full revolu-
tions in the 0Ω to 200Ω range of the multiturn
potentiometer). This sets the regulation point for the
laser bias current to 0.25V / 100Ω = 2.5mA.
7) Set potentiometer R4 (R
MOD
) to maximum resis-
tance by turning the screw counterclockwise until a
faint click is felt (30 full revolutions in the 0Ω to
50kΩ range of the multiturn potentiometer). This
minimizes the modulation current.
8) Set potentiometer R3 (R
TC
) to maximum resistance
by turning the screw counterclockwise until a faint
click is felt (30 full revolutions in the 0Ω to 100kΩ
range of the multiturn potentiometer). This mini-
mizes the tempco of the modulation current.
9) Place jumpers across JU2 (EN), JU3 (EN), and JU4
(PORDLY).
10) If you intend to power the board from a +5V supply,
place a jumper across JU1 (LV).
Do not apply
power yet.
11) Make sure there is no jumper on JU5 (FLTDLY).
12) Attach a cable with 50Ω characteristic impedance
between the J5 SMA output connector and the
input of the oscilloscope. Make sure the oscillo-
scope input is 50Ω terminated.
13) Attach differential sources to SMA connectors J1
and J2. Each source should have a peak-to-peak
amplitude between 100mV and 830mV.
14) Apply either +3.3V or +5V power to the board at
the J7 (VCC) and J8 (GND) test points. Set the cur-
rent limit to 300mA.
15) While monitoring the voltage on TP19, adjust R11
until the desired DC bias current is obtained.
Turning the R11 potentiometer screw clockwise
increases the DC bias current.
16) While monitoring the J5 SMA connector output on
the oscilloscope, adjust R4 (R
MOD
) until the
desired modulation current is obtained. Turning the
R4 potentiometer screw clockwise increases the
modulation current.
Evaluates: MAX3286/MAX3296
Electrical Quick Start with
Bias-Current Feedback (VCSEL)
1) Configure the board to directly regulate the DC bias
current. Set up the following shunts:
SHUNT
SP3
SP4
SP5
SP6
SP7
SP8
SP9
SP10
SP11
STATUS
Closed
Open
Closed
Closed
Open
Open
Closed
Closed
Open
Refer to the MAX3286/MAX3296 Common-Cathode
Laser Without Photodiode application circuit in the
MAX3286–MAX3289/MAX3296–MAX3299 data
sheet.
2) Make sure nothing is installed in the laser socket
(Figure 1).
_______________________________________________________________________________________
3
MAX3296 Shortwave or VCSEL
(Common Cathode) Evaluation Kit
Evaluates: MAX3286/MAX3296
Emulating a Photodiode During
Electrical Evaluation
When evaluating the MAX3286/MAX3296 without a
laser (see
Electrical Quick Start
sections), the
MAX3286/MAX3296 DC bias circuitry operates using a
photodiode emulator circuit. When shunts SP6 and SP7
are shorted, U2 (MAX4322), Q2 (FMMT491A), and R30
form a current-controlled current source that emulates
the behavior of the photodiode in the laser assembly.
R22 takes the place of the laser diode, and the photodi-
ode emulator circuitry sinks a current from the collector
of Q2 equal to 3% of the current through R22. This sim-
ulates the behavior of a laser diode and photodiode
assembly where a fraction of the laser light reflects onto
the photodiode, which then outputs a small current pro-
portional to the light emitted.
then clockwise for 15 full revolutions (30 full revolu-
tions in the 0Ω to 10kΩ range of the multiturn
potentiometer). This sets the regulation point for the
photodiode current to (2.65V - 1.7V) / 5kΩ = 190µA.
Set potentiometer R4 (R
MOD
) to maximum resis-
tance by turning the screw counterclockwise until a
faint click is felt (30 full revolutions in the 0Ω to
50kΩ range of the multiturn potentiometer). This
minimizes the modulation current (AC drive applied
to laser).
Set potentiometer R3 (R
TC
) to maximum resistance
by turning the screw counterclockwise until a faint
click is felt (30 full revolutions in the 0Ω to 100kΩ
range of the multiturn potentiometer). This mini-
mizes the tempco of the modulation current.
Set potentiometer R11 to 30Ω of resistance by turn-
ing the screw clockwise until a faint click is felt,
then counterclockwise five turns.
Attach a 50Ω SMA terminator to J5 to match the
laser loading.
Place jumpers across JU2 (EN), JU3 (EN), and JU4
(PORDLY).
If you intend to power the board from a +5V supply,
place a jumper across JU1 (LV).
Do not apply
power yet.
Make sure there is no jumper on JU5 (FLTDLY).
Attach differential sources to SMA connectors J1
and J2. Each source should have a peak-to-peak
amplitude between 100mV and 830mV.
Apply either +3.3V or +5V power to the board at
the J7 (VCC) and J8 (GND) test points.
While monitoring the laser output, adjust R5 (R
SET
)
until the desired laser bias current is obtained.
Turning the R5 potentiometer screw clockwise
increases the laser bias current.
While monitoring the laser output, adjust R4 (R
MOD
)
until the desired laser modulation current is
obtained. Turning the R4 potentiometer screw
clockwise increases the laser modulation current.
Look at the “eye” output on the oscilloscope. Laser
overshoot and ringing can be improved by appro-
priate selection of R13 and C12, as described in the
Designing the Laser-Compensation Filter Network
section of the MAX3286–MAX3289/MAX3296–
MAX3299 data sheet.
6)
7)
8)
_________________Optical Quick Start
Optical Quick Start with
Photodiode Feedback
1) Configure the board so that it will servo the laser
bias current, achieving a fixed photodiode current.
Set up the following shunts:
Refer to the MAX3286/MAX3296 Common-Cathode
Laser with Photodiode applications circuit in the
MAX3286–MAX3289/MAX3296–MAX3299 data
sheet.
SHUNT
SP3
SP4
SP5
SP6
SP7
SP8
SP9
SP10
SP11
STATUS
Open
Closed
Closed
Open
Open
Closed
Open
Open
Closed
9)
10)
11)
12)
13)
14)
15)
16)
2)
3)
4)
5)
Remove R24.
Install L8.
Connect a laser to the board (Figure 1).
Set potentiometer R5 (R
SET
) to midscale by turning
the screw counterclockwise until a faint click is felt,
17)
4
_______________________________________________________________________________________
MAX3296 Shortwave or VCSEL
(Common Cathode) Evaluation Kit
Optical Quick Start with
Bias-Current Feedback (VCSELs)
1) Configure the board to directly regulate the laser
bias current. Set up the following shunts:
Refer to the MAX3286/MAX3296 Common-Cathode
Laser Without Photodiode application circuit in the
MAX3286–MAX3289/MAX3296–MAX3299 data
sheet.
SHUNT
SP3
SP4
SP5
SP6
SP7
SP8
SP9
SP10
SP11
STATUS
Closed
Open
Closed
Open
Open
Open
Closed
Closed
Open
8) Attach a 50Ω SMA terminator to J5 to match the
laser loading.
9) Place jumpers across JU2 (EN), JU3 (EN), and JU4
(PORDLY).
10) If you intend to power the board from a +5V supply,
place a jumper across JU1 (LV).
Do not apply
power yet.
11) Make sure there is no jumper on JU5 (FLTDLY).
12) Attach differential sources to SMA connectors J1
and J2. Each source should have a peak-to-peak
amplitude between 100mV and 830mV.
13) Apply either +3.3V or +5V power to the board at
the J7 (VCC) and J8 (GND) test points. Set the cur-
rent limit to 300mA.
14) While monitoring the laser output, adjust R11 until
the desired DC bias current is obtained. Turning
the R11 potentiometer screw clockwise increases
the DC bias current.
15) While monitoring the laser output, adjust R4
(R
MOD
) until the desired modulation current is
obtained. Turning the R4 potentiometer screw
clockwise increases the modulation current.
16) Look at the “eye” output on the oscilloscope. Laser
overshoot and ringing can be improved by appro-
priate selection of R13 and C12 as described in the
Designing the Laser-Compensation Filter Network
section of the MAX3286–MAX3289/MAX3296–
MAX3299 data sheet.
S
M
A
2
Evaluates: MAX3286/MAX3296
2)
3)
4)
5)
Remove R24.
Install L8.
Connect a laser to the board (Figure 1).
Set potentiometer R11 to midscale by turning the
screw counterclockwise until a faint click is felt,
then clockwise for 15 full revolutions (30 full revolu-
tions in the 0Ω to 200Ω range of the multiturn
potentiometer). This sets the regulation point for the
laser bias current to 0.25V / 100Ω = 2.5mA.
6) Set potentiometer R4 (R
MOD
) to maximum resis-
tance by turning the screw counterclockwise until a
faint click is felt (30 full revolutions in the 0Ω to
50kΩ range of the multiturn potentiometer). This
minimizes the modulation current.
7) Set potentiometer R3 (R
TC
) to maximum resistance
by turning the screw counterclockwise until a faint
click is felt (30 full revolutions in the 0Ω to 100kΩ
range of the multiturn potentiometer). This mini-
mizes the tempco of the modulation current.
1
4
1, 3 = GROUND
2 = LASER-DIODE ANODE
4 = PHOTODIODE CATHODE
(LASER-DIODE CATHODE/PHOTODIODE
ANODE)
3
MAX3286
MAX3296
Figure 1. Optical Connection Diagram
_______________________________________________________________________________________
5
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