MAXIM MAX3996EVKIT

19-2356; Rev 0; 3/02
MAX3996 Evaluation Kit
Features
♦ Drives Common-Anode Lasers
The output of the electrical evaluation section is interfaced to an SMA connector that can be connected to a
50Ω terminated oscilloscope. The output of the optical
evaluation section is configured for attachment to a
laser/monitor diode.
♦ LED Fault Indicator
♦ Fully Assembled and Tested
♦ Adjustable Laser Bias Current
♦ Adjustable Laser Modulation Current
♦ Adjustable Laser Modulation Temperature
Coefficient
♦ Configured for Electrical Operation; No Laser
Necessary
Component Suppliers
Ordering Information
SUPPLIER
AVX
PHONE
803-946-0690
FAX
803-626-3123
PART
TEMP RANGE
Coilcraft
847-639-6400
847-639-1469
MAX3996EVKIT
0°C to +70°C
Murata
814-237-1431
814-238-0490
Zetex
516-543-7100
516-864-7630
PINPACKAGE
20 QFN
TOP
MARK
—
Component List
DESIGNATION
QTY
C1
1
C2, C3, C7,
C9, C10, C15,
C16, C21,
C26, C44,
C48, C49
12
C4, C24
2
DESCRIPTION
0.1µF ±10% 10V ceramic
capacitor (0402)
0.01µF ±10% ceramic
capacitors (0402)
DESIGNATION
QTY
DESCRIPTION
L2, L3, L6
3
Ferrite beads
Murata BLM18HG102SN-1
Q1, Q7
2
Transistors
Zetex FMMT591A NPN
Q3
1
Transistor
Zetex FMMT491A PNP
R1
1
10kΩ variable resistor
10µF ±10% tantalum
capacitors
AVX TAJC106K016
R2, R16
2
0Ω resistors (0402)
R3
1
Open, user-supplied
1
Open, user-supplied*
R4
1
4.3kΩ ±5% resistor (0402)
C33
1
0.01µF ±10% ceramic
capacitor (0603)
R5
1
1kΩ ±5% resistor (0402)
1.8kΩ ±5% resistor (0402)
D1
1
LED, T1 Package
D2
1
Open, user-supplied laser
J1, J2, J3
3
SMA connectors (edge mount)
R15
1
511Ω ±1% resistor (0402)
J4
1
1 × 3-pin header (0.1in centers)
R17
1
24.9Ω ±1% resistor (0402)*
J5, J8, J9
3
Test points
R19
1
49.9Ω ±1% resistor (0402)
JU7
1
Shunt
R27
1
24.9Ω ±1% resistor (0402)**
L1, L7
2
Ferrite beads
Murata BLM18HG601SN-1
R39
1
1kΩ ±5% resistor (0603)
R40
1
10Ω ±5% resistor (0603)
C18
R6
1
R7, R14
2
100kΩ variable resistors
R8
1
50kΩ variable resistor
________________________________________________________________ Maxim Integrated Products
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.
1
Evaluates: MAX3996
General Description
The MAX3996 evaluation kit (EV kit) is an assembled
demonstration board that provides both optical and electrical evaluation of the MAX3996 2.5Gbps laser driver.
Evaluates: MAX3996
MAX3996 Evaluation Kit
Component List (continued)
DESIGNATION
QTY
TP1-TP6,
TP11, TP12
8
DESCRIPTION
Test points
U1
1
MAX3996CGP (20-QFN)
U6
1
MAX4322EUK-T (5-SOT23)
None
1
MAX3996 EV kit circuit board,
rev B
None
1
MAX3996 data sheet
*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. R17
and C18 add a pole to cancel this zero. Starting values for most
coaxial lasers is R17 = 24.9Ω in series with C18 = 2pF. These
values should be experimentally adjusted until the output waveform is optimized.
**For electrical evaluation only.
Quick Start
Electrical Evaluation
In the electrical configuration, a test circuit is included
to emulate a semiconductor laser with a monitor photodiode. Monitor diode current is provided by Q7, which
is controlled by an operational amplifier (U6). The test
circuit consisting of U6 and Q7 applies the simulated
monitor diode current (the laser bias current divided by
a factor of 100) to the MD pin of the MAX3996. To
ensure proper operation in the electrical configuration,
set up the evaluation board as follows:
1) Ensure that SP9 and SP10 are shorted in order to
use the photodiode emulator circuitry. Ensure that
SP1 is open.
2) Make sure nothing is installed in the laser socket
(Figure 1).
3) Ensure that R27 is installed.
4) Confirm that C18 is open.
5) Set potentiometers R1 and R14 (RSET = R1 + R14)
to midscale by turning their screws clockwise at
least 30 revolutions or until they faintly click, and
then counterclockwise for 15 revolutions. This sets
the regulation point for the simulated photodiode
current to 1.12V/(5kΩ + 50kΩ) = 20.4µA. The photodiode emulator circuit regulates the DC bias current
into Q7 to 100 ✕ 20.4µA ≈ 2mA.
until it clicks faintly (30 full revolutions in the 0Ω to
50kΩ range of the multiturn potentiometer). This
minimizes the modulation current.
7) Set the potentiometer R7 (RTC) to maximum resistance by turning the screw counterclockwise until it
clicks faintly (30 revolutions in the 0Ω to 100kΩ
range of the multiturn potentiometer). This minimizes the temperature coefficient (tempco) of the
modulation current.
8) Place jumpers across pin 2 (TX_DISABLE) and pin
3 (GND) of J4 (pin 1 is the square pad). This
enables the output.
9) Attach a high-speed oscilloscope with 50Ω inputs to
J1 (OUT+) through a 50Ω characteristic impedance
cable.
10) Apply a differential input signal to J2 (IN+) and J3
(IN-). Set the differential amplitude between
200mVP-P and 2200mVP-P. Note that the differential
amplitude is twice the single-ended amplitude.
11) Apply a power-supply voltage of either 3.3V or 5V
between J8 (VCC) and J9 (GND). Set the current
limit to 300mA.
12) Apply 5V between J5 (5V) and J9 (GND). Set the
current limit to 100mA. This provides power to the
photodiode feedback emulator.
13) Adjust R8 (RMODSET) until the desired laser modulation current is achieved.
IMOD =
Signal Amplitude (V)
25Ω
Optical Evaluation
For optical evaluation of the MAX3996, configure the
evaluation kit as follows:
1) Open SP9 and SP10 and short SP1. This disconnects the photodiode emulator circuitry and attaches the bias to the laser.
2) Remove R27.
3) Connect a laser to the board (Figure 1).
4) Set potentiometers R1 and R14 (RSET = R1 + R14)
to midscale by turning the screws clockwise at least
30 revolutions or until they click faintly, and then
counterclockwise 15 revolutions. This sets the regulation point for the photodiode current to 1.12V/(5kΩ
+ 50kΩ) = 20.4µA. The resulting laser bias current
depends on the relationship between laser power
and photodiode output current.
6) Set the potentiometer R8 (RMODSET) to maximum
resistance by turning the screw counterclockwise
2
_______________________________________________________________________________________
MAX3996 Evaluation Kit
5) Set the potentiometer R8 (RMODSET) to maximum
resistance by turning the screw counterclockwise
until it clicks faintly (30 full revolutions in the 0Ω to
50kΩ range of the multiturn potentiometer). This
minimizes the modulation current.
6) Set the potentiometer R7 (RTC) to maximum resistance by turning the screw counterclockwise until it
clicks faintly (30 revolutions in the 0Ω to 100kΩ
range of the multiturn potentiometer). This minimizes the temperature coefficient (tempco) of the
modulation current.
7) Attach a 50Ω SMA terminator to J1 (OUT+). This
balances the load on the differential outputs of the
MAX3966.
8) Place jumpers across pin 2 (TX_DISABLE) and pin
3 (GND) of J4 (pin 1 is the square pad). This
enables the output.
9) Apply a differential input signal to J2 (IN+) and J3
(IN-). Set the differential amplitude between
200mVP-P and 2200mVP-P. Note that the differential
amplitude is twice the single-ended amplitude.
10) Apply a power-supply voltage of either 3.3V or 5V
between J8 (VCC) and J9 (GND). Set the current
limit to 300mA.
11) Adjust R1 and R14 (R SET = R1 + R14) until the
desired laser bias current is achieved. Turning the
R1 and R14 potentiometer screws clockwise
increases the laser bias current.
12) Adjust R8 (RMODSET) until the desired modulation
current is achieved. Turning the R8 potentiometer
screw clockwise increases the laser modulation
current.
13) Look at the “eye” output on an oscilloscope. Laser
overshoot and ringing can be improved by appropriate selection of R17 and C18, as described in the
Design Procedure section of the MAX3996 data sheet.
Adjustment and Control Descriptions (see Quick Start first)
COMPONENT
NAME
FUNCTION
C21
CPORDLY
Removing C21 floats PORDLY pin and minimizes the power-on reset time. Refer to the
Design Procedures section of the MAX3996 data sheet.
D1
Fault
Indicator
The LED is illuminated when a fault condition has occurred. The fault condition can be
cleared by removing and then reinstalling the jumper at J4.
J4
TX_DISABLE
R1, R14
RSET
The series combination of potentiometers R1 and R14 sets the desired laser DC-current
bias point. They set the resistance from MD to ground. Turn the potentiometer screws
clockwise to increase average power (decrease the resistance).
R7
RTC
Potentiometer R7 (RTC), in conjunction with potentiometer R8 (RMODSET), sets the tempco
of the laser modulation current. Turn the potentiometer screw clockwise (decrease the
resistance) to increase the tempco.
R8
RMODSET
Potentiometer R8 (RMODSET), in conjunction with potentiometer R7 (RTC), sets the peak-topeak amplitude of the laser modulation current. Turn the potentiometer screw clockwise
(decrease the resistance) to increase the modulation amplitude.
SP1, SP9, SP10

Open SP1, short SP9, and short SP10 with a solder bridge for electrical evaluation. Short
SP1, open SP9, and open SP10 for optical evaluation.
Placing a jumper across pin 1 (VCC) and pin 2 (TX_DISABLE) of J4 disables the output
(active high). Place a jumper across pin 2 (TX_DISABLE) and pin 3 (GND) of J4 to enable
the outputs (pin 1 is the square pad).
_______________________________________________________________________________________
3
Evaluates: MAX3996
WARNING: Consult your laser data sheet to ensure
that 20µA of photodiode monitor current does not
correspond to excessive laser power.
Evaluates: MAX3996
MAX3996 Evaluation Kit
5V
LASER SOCKET
4
VCC
1
1: VCC
3
2: LASER CATHODE
3: VCC WITH SHUTDOWN
GND
2
4: PHOTODIODE ANODE
MAX3996
Figure 1. Optical Connection Diagram
4
_______________________________________________________________________________________
Q3
FMMT491A
J1
TP3
FAULT
INDICATOR
R15
511Ω
R4
4.3kΩ
VCC2
J9
J8
D1
LED
OUT+
GND
VCC
5V
J4
R7
100kΩ
TP11
C16
0.01µF
C24
10µF
C4
10µF
VCC2
RTC
R19
49.9Ω
L7
L1
RMODSET
C26
0.01µF
C3
0.01µF
5
4
3
2
1
C7
0.01µF
VC C2
C21
0.01µF
R8
50kΩ
TP12
L3
VCC2
VCC1
VCC
TP2
IN+
J3
IN-
9
J2
8
GND
OUT+
17
C10
0.01µF
7
6
IN-
MAX3996
U1
OUT-
18
L6
C9
0.01µF
IN+
VCC
PORDLY
TX_DISABLE
GND
FAULT
TC
19
20
C49
0.01µF
MODSET
VCC2
C15
0.01µF
C18
OPEN
R17
24.9Ω
VCC2
BIAS
10
R2
0Ω
MON1
MON2
COMP
MD
C48
0.01µF
11
12
13
14
15
VCC2
SHDNDRV
VCC
16
R16
0Ω
C1
0.1µF
R5
1kΩ
R3
OPEN
TP1
SP1
L2
R27
24.9Ω
TP4
TP5
BIAS
MD
C2
0.01µF
R1
10kΩ
RSET
LASER
SP10
SP9
R6
1.8kΩ
R14
100kΩ
TP6
Q7
FMMT591A
BIAS
PHOTODIODE
FEEDBACK
EMULATOR
U6
Q1
FMMT591A
D2
OPEN
TP13
VCC1
VCC2
R40
10Ω
VCC2
C33
0.01µF
PHOTODIODE
MAX4322
R39
1kΩ
VCC2
MD
C44
0.01µF
Evaluates: MAX3996
J5
MAX3996 Evaluation Kit
Figure 2. MAX3996 EV Kit Schematic
_______________________________________________________________________________________
5
Evaluates: MAX3996
MAX3996 Evaluation Kit
Figure 3. MAX3996 EV Kit Component Placement Guide—
Component Side
6
Figure 4. MAX3996 EV Kit PC Board Layout—Component Side
_______________________________________________________________________________________
MAX3996 Evaluation Kit
Evaluates: MAX3996
Figure 5. MAX3996 EV Kit PC Board Layout—Ground Plane
Figure 6. MAX3996 EV Kit PC Board Layout—Power Plane
Figure 7. MAX3996 EV Kit PC Board Layout—Solder Side
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 _____________________ 7
© 2002 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.