________________General Description
The MAX3263 is a complete, easy-to-program, single
+5V-powered, 155Mbps laser diode driver with com-
plementary enable inputs and automatic power control
(APC). The MAX3263 accepts differential PECL inputs
and provides complementary output currents. A tem-
perature-stabilized reference voltage is provided to
simplify laser current programming. This allows modu-
lation current to be programmed up to 30mA and bias
current to be programmed from up to 60mA with two
external resistors.
An APC circuit is provided to maintain constant laser
power in transmitters that use a monitor photodiode.
Only two external resistors are required to implement
the APC function.
The MAX3263’s fully integrated feature set includes a
TTL-compatible laser failure indicator and a program-
mable slow-start circuit to prevent laser damage. The
slow-start is preset to 50ns and can be extended by
adding an external capacitor.
________________________Applications
Laser Diode Transmitters
155Mbps SDH/SONET
155Mbps ATM
____________________________Features
♦Rise Times Less than 1ns
♦Differential PECL Inputs
♦Single +5V Supply
♦Automatic Power Control
♦Temperature-Compensated Reference Voltage
♦Complementary Enable Inputs
_______________Ordering Information
MAX3263
Single +5V, Fully Integrated,
155Mbps Laser Diode Driver
________________________________________________________________
Maxim Integrated Products
1
24
23
22
21
20
19
18
17
1
2
3
4
5
6
7
8
SLWSTRT
IPIN
VCCA
GNDA
OUT+
GNDA
OUT-
GNDA
IBIASOUT
IMODSET
IBIASSET
IBIASFB
VREF2
IPINSET
FAILOUT
GNDB
VIN+
VIN-
GNDB
VCCB
ENB-
ENB+
VREF1
OSADJ
TOP VIEW
16
15
14
13
9
10
11
12
SSOP
MAX3263
___________________Pin Configuration
19-0432; Rev 1b; 4/98
PART
MAX3263CAG 0°C to +70°C
TEMP. RANGE PIN-PACKAGE
24 SSOP
MAX3263
+5V
0.01µF 0.01µF
+5V
+5V
+5V
OUT+
IBIASOUT
IPIN
PECL
INPUTS
OUT-
FAILOUT
IBIASFB
OSADJ
IMODSETIPINSET
IBIASSET
VCCA VCCB
VIN+
VIN-
ENB+
GNDB
GNDA
ENB-
SLWSTRT
VREF1
VREF2
LASER
2.7k
PHOTO-
DIODE
FERRITE BEAD
_____________Typical Operating Circuit
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.
For small orders, phone 1-800-835-8769.
MAX3263
Single +5V, Fully Integrated,
155Mbps Laser Diode Driver
2 _______________________________________________________________________________________
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
TA = +25°C
(Note 1)
CONDITIONS
mA12IREF
Available Reference Current
V3.15 3.3 3.45VREF
mA60IBIAS
Range of Programmable Laser
Bias Current
Reference Voltage
VVIL
TTL Low Input
mA50IVCC
Supply Current
VVCC - 1.165VIH
PECL Input High
VVCC - 1.475VIL
PECL Input Low
V2 0.8VIH
TTL High Input
UNITSMIN TYP MAXSYMBOLPARAMETER
Minimum differential input swing is 1100mVp-p
(Note 3)
CONDITIONS
mA30IMOD
Range of Programmable
Modulation Current
UNITSMIN TYP MAXSYMBOLPARAMETER
IBIAS = 25mA, IMOD = 12mA, 4ns unit interval;
measured from 10% to 90% ns1tR, tF
Modulation-Current Rise and
Fall Time
IMOD = 12mA, TA= +25°C %±15OS
Aberrations, Rising and Falling
Edge
IBIAS = 25mA, IMOD = 12mA, 8ns period ps100PWD
Modulation-Current Pulse-
Width Distortion
ABSOLUTE MAXIMUM RATINGS
Terminal Voltage (with respect to GND)
Supply Voltages (VCCA, VCCB).............................-0.3V to +6V
VIN+, VIN-, FAILOUT ................................................0V to VCC
OUT+, OUT-, IBIASOUT ......................................+1.5V to VCC
ENB+, ENB- ......................VCC or +5.5V, whichever is smaller
Differential Input Voltage (|VIN+ - VIN-|).........................+3.8V
Input Current
IBIASOUT ............................................................0mA to 75mA
OUT+, OUT- ........................................................0mA to 40mA
IBIASSET ........................................................0mA to 1.875mA
IMODSET...............................................................0mA to 2mA
IPIN, IPINSET, OSADJ...........................................0mA to 2mA
FAILOUT..............................................................0mA to 10mA
IBIASFB................................................................-2mA to 2mA
Output Current
VREF1, VREF2.....................................................0mA to 20mA
SLWSTRT ..............................................................0mA to 5mA
Continuous Power Dissipation (TA= +70°C)
SSOP (derate 8mW/°C above +70°C) ..........................640mW
Operating Temperature Range...............................0°C to +70°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-55°C to +175°C
DC ELECTRICAL CHARACTERISTICS
(VCC = VCCA = VCCB = +4.75V to +5.25V, TA= 0°C to +70°C, unless otherwise noted. Typical values are at VCC = +5V and
TA= +25°C.)
AC ELECTRICAL CHARACTERISTICS
(VCC = VCCA = VCCB = +4.75V to +5.25V, RLOAD (at OUT+ and OUT-) = 25Ωconnected to VCC, TA= 0°C to +70°C, unless other-
wise noted. Typical values are at VCC = +5V and TA= +25°C.) (Note 2)
Loaded with 2.7kΩpull-up resistor to VCC
Loaded with 2.7kΩpull-up resistor to VCC
V0.5VOL
FAILOUT Output Low
V4.5VOH
FAILOUT Output High
Note 2: AC characteristics are guaranteed by design and characterization.
Note 3: An 1100mVp-p differential is equivalent to complementary 550mVp-p signals on VIN+ and VIN-.
Note 1: IVCC = IVCCA + IVCCB, IBIAS = 60mA, IMOD = 30mA, and IPIN = 140µA.
MAX3263
Single +5V, Fully Integrated,
155Mbps Laser Diode Driver
_______________________________________________________________________________________
3
0
02040
RBIASSET vs. BIAS CURRENT
5
MAX3263-01
IBIAS (mA)
RBIASSET (kΩ)
60
3
1
4
2
6
7
8
0
0 5 10 15 20 25
RMODSET vs. MODULATION CURRENT
8
MAX3263-02
MODULATION CURRENT (mAp-p)
RMODSET (kΩ)
30
6
4
2
10
12 DIFFERENTIAL INPUT
SWING = 1100 mVp-p
100
0 500
RPINSET vs. MONITOR CURRENT
MAX3263-03
MONITOR CURRENT (µA)
RPINSET (Ω)
1000
10,000
1000
100,000
1,000,000
-10
-8
-6
-4
-2
0
2
4
6
8
10
02040
PERCENT CHANGE IN MODULATION
CURRENT vs. TEMPERATURE
MAX3263-04
TEMPERATURE (°C)
% CHANGE (w.r.t. +25°C)
8060
-2
-1
0
1
2
3
02040
PERCENT CHANGE IN BIAS
CURRENT vs. TEMPERATURE
MAX3263-05
TEMPERATURE (°C)
% CHANGE (w.r.t. +25°C)
806010 30 7050
APC DISABLED
34
36
38
40
42
44
46
48
50
02040
SUPPLY CURRENT
vs. TEMPERATURE
MAX3263-06
TEMPERATURE (°C)
SUPPLY CURRENT (mA)
8060
0
0 5 10 15 20 25
ALLOWABLE ROSADJ RANGE
vs. MODULATION CURRENT
8
MAX3263-07
MODULATION CURRENT (mAp-p)
ALLOWABLE ROSADJ (kΩ)
30
6
4
2
10
12
ALLOWABLE
RANGE
0
0 400 800 1200 1600
MAXIMUM MODULATION CURRENT
vs. MINIMUM DIFFERENTIAL
INPUT SIGNAL AMPLITUDE
25
MAX3263-08
MINIMUM DIFFERENTIAL
INPUT SIGNAL AMPLITUDE (mVp-p)
MAXIMUM MODULATION CURRENT (mAp-p)
2000
20
15
10
5
30
35
40 RMODSET = 1.2kΩ
ROSADJ = 2kΩ
__________________________________________Typical Operating Characteristics
(MAX3263CAG loads at OUT+ and OUT- = 25Ω, VCC = VCCA = VCCB = +5V, TA= +25°C, unless otherwise noted.)
MAX3263
Single +5V, Fully Integrated,
155Mbps Laser Diode Driver
4 _______________________________________________________________________________________
______________________________________________________________Pin Description
NAME FUNCTIONPIN
10 ENB+ Noninverting Enable TTL Input. Output currents are enabled only when ENB+ is high and
ENB- is low.
1 VREF2 Temperature-Compensated Reference Output. VREF2 is internally connected to VREF1.
12 OSADJ Overshoot-Adjust Input. Connect to internal voltage reference through a resistor to adjust the
overshoot of the modulation output signal (see
Typical Operating Characteristics
).
11 VREF1 Temperature-Compensated Reference Output. VREF1 is internally connected to VREF2.
13 IBIASFB Bias-Feedback Current Output. Output from automatic power-control circuit. Connect to
IBIASSET when using APC.
14 IBIASSET
Laser Bias Current-Programming Input. Connect to internal voltage reference through a resis-
tor to set bias current (see
Typical Operating Characteristics
).
IBIASOUT = 40 x (IBIASSET + IBIASFB).
15 IMODSET
Laser Modulation Current-Programming Input. Connect to internal voltage reference through
a resistor to set modulation current (see
Typical Operating Characteristics
).
IMOD = 20 x IMODSET.
16 IBIASOUT Laser Bias Current Output. Connect to laser cathode through an R-L filter network (see the
Bias Network Compensation
section).
17, 19, 21 GNDA Ground for Bias and Modulation Current Drivers
22 VCCA +5V Supply Voltage for Bias and Modulation Current Drivers. Connect VCCA to the same
potential as VCCB, but provide separate bypassing for VCCA and VCCB.
20 OUT+ Modulation Output. When VIN+ is low and VIN- is high, OUT+ sinks IMOD.
9 ENB- Inverting Enable TTL Input. Output currents are enabled only when ENB+ is high and ENB- is low.
8 VCCB +5V Supply Voltage for Voltage Reference and Automatic Power-Control Circuitry. Connect
VCCB to the same potential as VCCA, but provide separate bypassing for VCCA and VCCB.
6 VIN- Inverting PECL Data Input
5 VIN+ Noninverting PECL Data Input
4, 7 GNDB Ground for Voltage Reference and Automatic Power-Control Circuitry
3 FAILOUT
Failout Output. Active-low, open-collector TTL output indicates if automatic power-control
loop is out of regulation due to insufficient monitor-diode current (when VPIN is below the
2.6V threshold). Connect FAILOUT to VCC through a 2.7kΩpull-up resistor.
2 IPINSET
Monitor Photodiode Programming Input. Connect INPINSET to VREF1 or VREF2 through a
resistor to set the monitor current when using automatic power control (see
Typical Operating
Characteristics
).
18 OUT- Modulation Output. When VIN+ is high and VIN- is low, OUT- sinks IMOD.
23 IPIN Monitor Photodiode Current Input. Connect IPIN to photodiode’s anode.
24 SLWSTRT Slow-Start Capacitor Input. Connect capacitor to ground or leave unconnected to set start-up
time, tSTARTUP = 25.4kΩ(CSLWSTRT +2pF).
MAX3263
Single +5V, Fully Integrated,
155Mbps Laser Diode Driver
_______________________________________________________________________________________ 5
_______________Detailed Description
The MAX3263 laser driver has three main sections: a
reference generator with temperature compensation, a
laser bias block with automatic power control, and a
modulation driver (Figure 1).
The reference generator provides temperature-com-
pensated biasing and a voltage-reference output. The
voltage reference is used to program the current levels
of the high-speed modulation driver, laser diode, and
PIN (p+, intrinsic, n-) monitor diode.
The laser bias block sets the bias current in the laser
diode and maintains it above the threshold current. A
current-controlled current source (current mirror) pro-
grams the bias, with IBIASSET as the input. The mirror’s
gain is approximately 40 over the MAX3263’s input
range. Keep the output voltage of the bias stage above
2.2V to prevent saturation.
The modulation driver consists of a high-speed input
buffer and a common-emitter differential output stage.
The modulation current mirror sets the laser modulation
current in the output stage. This current is switched
between the OUT+ and OUT- ports of the laser driver.
The modulation current mirror has a gain of approximately
20. Keep the voltages at OUT+ and OUT- above 2.2V to
prevent saturation.
MAX3263
VCCB
VCC
20 x IMODSET
40 x IBIASSET
IBIASOUT
IPIN
IPINSET
RPINSET
1 x IPINSET
IBIASSET
IBIASFB
RBIASSET
IMODSET
RMODSET
ROSADJ IOSADJ
VIN+
VIN-
ENB+
GNDA
ENB-
SLWSTRT
VREF1, VREF2
LASER
PHOTO-
DIODE
LOOP-
STABILITY
CAPACITOR
0.1µF
GNDB
VCCA
OUT+
OUT-
FAILOUT
+2.6V
COMPARATOR
VCC x 3/5
TRANSCONDUCTANCE
AMPLIFIER
MAIN
BIAS
GENERATOR
BANDGAP
REFERENCE
BIAS
COMPEN-
SATION
Figure 1. Functional Diagram
The overshoot mirror sets the bias in the input buffer
stage (Figure 2). Reducing this current slows the input
stage and reduces overshoot in the modulation signal.
At the same time, the peak-to-peak output swing of the
input buffer stage is reduced. Careful design must be
used to ensure that the buffer stage can switch the out-
put stage completely into the nonlinear region. The
input swing required to completely switch the output
stage depends on both ROSADJ and the modulation
current. See Allowable ROSADJ Range vs. Modulation
Current and Maximum Modulation Current vs. Minimum
Differential Input Signal Amplitude graphs in the
Typical
Operating Characteristics
. For the output stage, the
width of the linear region is a function of the desired
modulation current. Increasing the modulation current
increases the linear region. Therefore, increases in the
modulation current require larger output levels from the
first stage.
Failure to ensure that the output stage switches com-
pletely results in a loss of modulation current (and
extinction ratio). In addition, if the modulation port does
not switch completely off, the modulation current will
contribute to the bias current, and may complicate
module assembly.
Automatic Power Control
The automatic power control (APC) feature allows an
optical transmitter to maintain constant power, despite
changes in laser efficiency with temperature or age. The
APC requires the use of a monitor photodiode.
The APC circuit incorporates the laser diode, the monitor
photodiode, the pin set current mirror, a transconduc-
tance amplifier, the bias set current mirror, and the laser
fail comparator (Figure 1). Light produced by the laser
diode generates an average current in the monitor pho-
todiode. This current flows into the MAX3263’s IPIN
input. The IPINSET current mirror draws current away
from the IPIN node. When the current into the IPIN node
equals the current drawn away by IPINSET, the node
voltage is set by the VCC x 3/5 reference of the transcon-
ductance amplifier. When the monitor current exceeds
IPINSET, the IPIN node voltage will be forced higher. If
the monitor current decreases, the IPIN node voltage is
decreased. In either case, the voltage change is ampli-
fied by the transconductance amplifier, and results in a
feedback current at the IBIASFB node. Under normal
APC operation, IBIASFB is summed with IBIASSET, and
the laser bias level is adjusted to maintain constant out-
put power. This feedback process continues until the
monitor-diode current equals IPINSET.
If the monitor-diode current is sufficiently less than IPIN-
SET (i.e., the laser stops functioning), the voltage on the
IPIN node drops below 2.6V. This triggers the failout
comparator, which provides a TTL signal indicating laser
failure. The FAILOUT output asserts only if the monitor-
diode current is low, not in the reverse situation where
the monitor current exceeds IPINSET. FAILOUT is an
open-collector output that requires an external pull-up
resistor of 2.7kΩto VCC.
The transconductance amplifier can source or sink cur-
rents up to approximately 1mA. Since the laser bias gen-
erator has a gain of approximately 40, the APC function
has a limit of approximately 40mA (up or down) from the
initial set point. To take full advantage of this adjustment
range, it may be prudent to program the laser bias cur-
rent slightly higher than required for normal operation.
However, do not exceed the IBIASOUT absolute maxi-
mum rating of 75mA.
To maintain APC loop stability, a 0.1µF bypass capaci-
tor may be required across the photodiode. If the APC
function is not used, disconnect the IBIASFB pin.
Enable Inputs
The MAX3263 provides complementary enable inputs
(ENB+, ENB-). The laser is disabled by reducing the ref-
erence voltage outputs (VREF1, VREF2). Only one logic
state enables laser operation (Figure 3 and Table 1).
MAX3263
Single +5V, Fully Integrated,
155Mbps Laser Diode Driver
6 _______________________________________________________________________________________
VCC
OUTPUTS
280Ω280Ω
9Ω
400Ω
9Ω
2(IOSADJ)IMOD
2(IOSADJ)
INPUT BUFFER OUTPUT STAGE
INPUTS
MAX3263
Figure 2. MAX3263 Modulation Driver (Simplified)
Temperature Considerations
The MAX3263 output currents are programmed by cur-
rent mirrors. These mirrors each have a 2VBE temperature
coefficient. The reference voltage (VREF) is adjusted 2VBE
so these changes largely cancel, resulting in output cur-
rents that are very stable with respect to temperature (see
Typical Operating Characteristics
).
__________________Design Procedure
Interfacing Suggestions
Use high-frequency design techniques for the board
layout of the MAX3263 laser driver. Adding some damp-
ing resistance in series with the laser raises the load
impedance and helps reduce power consumption (see
Reducing Power Consumption
section). Minimize any
series inductance to the laser, and place a bypass
capacitor as close to the laser’s anode as possible.
Power connections labeled VCCA are used to supply the
laser modulation and laser bias circuits. VCCB connec-
tions supply the bias-generator and automatic-power
control circuits. For optimum operation, isolate these sup-
plies from each other by independent bypass filtering.
GNDA and GNDB have multiple pins. Connect all pins
to optimize the MAX3263’s high-frequency perfor-
mance. Ground connections between signal lines
(VIN+, VIN-, OUT+, OUT-) improve the quality of the
signal path by reducing the impedance of the intercon-
nect. Multiple connections, in general, reduce induc-
tance in the signal path and improve the high-speed
signal quality. GND pins should be tied to the ground
plane with short runs and multiple vias. Avoid ground
loops, since they are a source of high-frequency inter-
ference.
The MAX3263 data inputs accept PECL input signals,
which require 50Ωtermination to (VCC - 2V). Figure 4
shows alternative termination techniques. When a ter-
mination voltage is not available, use the Thevenin-
equivalent termination. When interfacing with a
non-PECL signal source, use one of the other alterna-
tive termination methods shown in Figure 4.
Bias Network Compensation
For best laser transmitter performance, add a filter to the
circuit. Most laser packages (TO-46 or DIL) have a sig-
nificant amount of package inductance (4nH to 20nH),
which limits their usable data rate. The MAX3263 OUT
pin has about 1pF of capacitance. These two parasitic
components can cause high-frequency ringing and
aberrations on the output signal.
If ringing is present on the transmitter output, try
adding a shunt RC filter to the laser cathode. This
limits the bandwidth of the transmitter to usable levels
and reduces ringing dramatically (Figure 5).
L = Laser inductance
C = Shunt filter capacitance
R = Shunt filter resistance
A good starting point is R = 25Ωand C = L / 4R.
Increase C until aberrations are reduced.
The IBIASOUT pin has about 4pF of parasitic capaci-
tance. When operating at bias levels over 50mA, the
impedance of the bias output may be low enough to
decrease the rise time of the transmitter. If this occurs,
the impedance of the IBIASOUT pin can be increased by
adding a large inductor in series with the pin.
Reducing Power Consumption
The laser driver typically consumes 40mA of current for
internal functions. Typical load currents, such as 12mA of
modulation current and 20mA of bias current, bring the
total current requirement to 72mA. If this were dissipated
entirely in the laser driver, it would generate 360mW of
MAX3263
Single +5V, Fully Integrated,
155Mbps Laser Diode Driver
_______________________________________________________________________________________ 7
Table 1. MAX3263 Truth Table
ENB- ENB+
0 0
0 1
1 0
1 1
VREF
Off
On
Off
Off
ENB+
DATA OUT
(LOAD = 1300nm
LASER AT OUT-)
2µs/div
Figure 3. Enable/Disable Operation
MAX3263
Single +5V, Fully Integrated,
155Mbps Laser Diode Driver
8 _______________________________________________________________________________________
THIS SYMBOL REPRESENTS
A TRANSMISSION LINE
WITH CHARACTERISTIC
IMPEDANCE Zo = 50Ω.
MAX3263
5V
120Ω
82Ω82Ω
5V
PECL
SIGNAL SOURCE
VIN+
VIN-
120Ω
a) THEVENIN-EQUIVALENT TERMINATION
MAX3263
68Ω
50Ω
50Ω
50Ω
5V
NON-PECL
SIGNAL SOURCE
VIN+
VIN-
180Ω
c) SINGLE-ENDED NON-PECL TERMINATION
MAX3263
1.8k
680Ω
50Ω
5V
NON-PECL
SIGNAL SOURCE VIN+
VIN-
5V
1.8k
680Ω
50Ω
b) DIFFERENTIAL NON-PECL TERMINATION
MAX3263
5V
3.6k
1.3k
1.3k
0V
ECL
SIGNAL SOURCE
-2V
VIN+
VIN-
3.6k
50Ω
50Ω
-2V
d) ECL TERMINATION
Figure 4. Alternative PECL Data-Input Terminations
heat. Fortunately, a substantial portion of this power is
dissipated across the laser diode. A typical laser diode
drops approximately 1.6V when forward biased. This
leaves 3.4V at the MAX3263’s OUT- terminal. It is safe to
reduce the output terminal voltage even further with a
series damping resistor. Terminal voltage levels down to
2.2V can be used without degrading the laser driver’s
high-frequency performance. Power dissipation can be
further reduced by adding a series resistor on the laser
driver’s OUT+ side. Select the series resistor so the
OUT+ terminal voltage does not drop below 2.2V with the
maximum modulation current.
_____________Applications Information
Programming the MAX3263 Laser Driver
Programming the MAX3263 is best explained by an
example. Assume the following laser diode characteris-
tics:
Wavelength λ1300nm
Threshold Current ITH 20mA at +25°C(+0.35mA/
°C temperature variation)
Monitor Responsivity ρmon 0.1A/W (monitor current /
average optical power
into the fiber)
Modulation Efficiency η0.1mW/mA (worst case)
Now assume the communications system has the fol-
lowing requirements:
Average Power PAVE 0dBm (1mW)
Extinction Ratio Er 6dB (Er = 4)
Temperature Range Tr 0°C to +70°C
1) Determine the value of IPINSET:
The desired monitor-diode current is (PAVE)(ρmon) =
(1mW)(0.1A/W) = 100µA. The RPINSET vs. Monitor
Current graph in the
Typical Operating Characteristics
show that RPINSET should be 18kΩ.
2) Determine RMODSET:
The average power is defined as (P1 + P0) / 2, where
P1 is the average amplitude of a transmitted “one” and
P0 is the average amplitude of a transmitted “zero.”
The extinction ratio is P1/P0. Combining these equa-
tions results in P1 = (2 x PAVE x Er) / (Er + 1) and P0 =
(2 x PAVE) / (Er + 1). In this example, P1 = 1.6mW and
P0 = 0.4mW. The optical modulation is 1.2mW. The
modulation current required to produce this output is
1.2mW / η= (1.2mW) / (0.1mA/mW) = 12mA. The
Typical Operating Characteristics
show that RMODSET
= 3.9kΩyields the desired modulation current.
3) Determine the value of ROSADJ:
Using the Allowable ROSADJ Range vs. Modulation
Current graph in the
Typical Operating Characteristics
,
a 5.6kΩresistor is chosen for 12mA of modulation cur-
rent. The maximum ROSADJ values given in the graph
minimize aberrations in the waveform and ensure that
the driver stage operates fully limited.
4) Determine the value of RBIASSET:
The automatic power control circuit can adjust the bias
current 40mA from the initial setpoint. This feature
makes the laser driver circuit reasonably insensitive to
variations of laser threshold from lot to lot. The bias set-
ting can be determined using one of two methods:
A) Set the bias at the laser threshold.
B) Set the bias at the midpoint of the highest and low-
est expected threshold values.
Method A is straightforward. In the second method, it is
assumed that the laser threshold will increase with age.
The lowest threshold current occurs at 0°C when the
laser is new. The highest threshold current occurs at
+70°C at the end of the product’s life. Assume the laser
is near the end of life when its threshold reaches two-
times its original value.
Lowest Bias Current:
ITH + ∆ITH = 20mA + (0.35mA/°C)(-25°C) = 11.25mA
Highest Bias Current:
2 x ITH + ∆ITH = 40mA + (0.35mA/°C)(+45°C) = 55.8mA
MAX3263
Single +5V, Fully Integrated,
155Mbps Laser Diode Driver
_______________________________________________________________________________________ 9
MAX3263
+5V
OUT+
OUT-
IPIN
≥0.1µF
IBIASOUT
25Ω
18Ω
18Ω
FERRITE
BEAD
LASER
SHUNT RC
PHOTO-
DIODE
0.01µF
AS CLOSE TO THE
LASER ANODE AS
POSSIBLE
AS CLOSE TO THE
LASER CATHODE AS
POSSIBLE
C
10µH
Figure 5. Typical Laser Interface with Bias Compensation
MAX3263
Single +5V, Fully Integrated,
155Mbps Laser Diode Driver
10 ______________________________________________________________________________________
______________________________________________________________________Package Information
In this case, set the initial bias value to 34mA (which is
the midpoint of the two extremes). The 40mA adjust-
ment range of the MAX3263 maintains the average
laser power at either extreme.
The
Typical Operating Characteristics
show that
RBIASSET = 1.8kΩdelivers the required bias current.
Laser Safety and IEC 825
Using the MAX3263 laser driver alone does not ensure
that a transmitter design is compliant with IEC 825 safe-
ty requirements. The entire transmitter circuit and com-
ponent selections must be considered. Each customer
must determine the level of fault tolerance required by
their application, recognizing that Maxim products are
not designed or authorized for use as components in
systems intended for surgical implant into the body, for
applications intended to support or sustain life, or for
any other application where the failure of a Maxim
product could create a situation where personal injury
or death may occur.
SSOP.EPS
MAX3263
Single +5V, Fully Integrated,
155Mbps Laser Diode Driver
______________________________________________________________________________________ 11
NOTES
MAX3263
Single +5V, Fully Integrated,
155Mbps Laser Diode Driver
NOTES
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.
12
____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 1998 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
Maxim makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does Maxim assume any lia-
bility arising out of the application or use of any product or circuit and specifically disclaims any and all liability, including without limitation consequential
or incidental damages. “Typical” parameters can and do vary in different applications. All operating parameters, including “typicals” must be validated for
each customer application by customer’s technical experts. Maxim products are not designed, intended or authorized for use as components in systems
intended for surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which the failure of the
Maxim product could create a situation where personal injury of death may occur.
