MAXIM MAX3263CAG

19-0432; Rev 1b; 4/98
Single +5V, Fully Integrated,
155Mbps Laser Diode Driver
____________________________Features
♦ Rise Times Less than 1ns
The MAX3263’s fully integrated feature set includes a
TTL-compatible laser failure indicator and a programmable slow-start circuit to prevent laser damage. The
slow-start is preset to 50ns and can be extended by
adding an external capacitor.
♦ Differential PECL Inputs
♦ Single +5V Supply
♦ Automatic Power Control
♦ Temperature-Compensated Reference Voltage
♦ Complementary Enable Inputs
_______________Ordering Information
PART
MAX3263CAG
TEMP. RANGE
0°C to +70°C
PIN-PACKAGE
24 SSOP
________________________Applications
Laser Diode Transmitters
_____________Typical Operating Circuit
155Mbps SDH/SONET
155Mbps ATM
___________________Pin Configuration
+5V
0.01µF
+5V
0.01µF
+5V
VCCA VCCB
TOP VIEW
VREF2 1
24 SLWSTRT
IPINSET 2
23 IPIN
FAILOUT 3
22 VCCA
GNDB 4
21 GNDA
VIN+ 5
MAX3263
OUT+
VIN+
VIN-
PHOTODIODE
GNDA
GNDB
19 GNDA
GNDB 7
18 OUT-
VCCB
17 GNDA
LASER
IPIN
MAX3263
ENB+
20 OUT+
VIN- 6
8
PECL
INPUTS
FERRITE BEAD
IBIASOUT
+5V
ENB-
OUT-
SLWSTRT
2.7k
FAILOUT
IBIASFB
ENB- 9
16 IBIASOUT
VREF1
ENB+ 10
15 IMODSET
VREF1 11
14 IBIASSET
VREF2
IBIASSET
IMODSET
OSADJ
IPINSET
OSADJ 12
13 IBIASFB
SSOP
________________________________________________________________ Maxim Integrated Products
1
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MAX3263
________________General Description
The MAX3263 is a complete, easy-to-program, single
+5V-powered, 155Mbps laser diode driver with complementary enable inputs and automatic power control
(APC). The MAX3263 accepts differential PECL inputs
and provides complementary output currents. A temperature-stabilized reference voltage is provided to
simplify laser current programming. This allows modulation 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.
MAX3263
Single +5V, Fully Integrated,
155Mbps Laser Diode Driver
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
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.
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.)
PARAMETER
SYMBOL
Range of Programmable Laser
Bias Current
IBIAS
Reference Voltage
VREF
Available Reference Current
IREF
Supply Current
IVCC
PECL Input High
VIH
CONDITIONS
TA = +25°C
MIN
TYP
3.15
3.3
MAX
UNITS
60
mA
3.45
V
12
mA
(Note 1)
50
VCC - 1.165
PECL Input Low
VIL
TTL High Input
VIH
TTL Low Input
VIL
FAILOUT Output High
VOH
Loaded with 2.7kΩ pull-up resistor to VCC
FAILOUT Output Low
VOL
Loaded with 2.7kΩ pull-up resistor to VCC
mA
V
VCC - 1.475
2
0.8
V
V
V
4.5
V
0.5
V
Note 1: IVCC = IVCCA + IVCCB, IBIAS = 60mA, IMOD = 30mA, and IPIN = 140µA.
AC ELECTRICAL CHARACTERISTICS
(VCC = VCCA = VCCB = +4.75V to +5.25V, RLOAD (at OUT+ and OUT-) = 25Ω connected to VCC, TA = 0°C to +70°C, unless otherwise noted. Typical values are at VCC = +5V and TA = +25°C.) (Note 2)
SYMBOL
CONDITIONS
MAX
UNITS
Range of Programmable
Modulation Current
PARAMETER
IMOD
Minimum differential input swing is 1100mVp-p
(Note 3)
30
mA
Modulation-Current Rise and
Fall Time
tR, tF
IBIAS = 25mA, IMOD = 12mA, 4ns unit interval;
measured from 10% to 90%
1
ns
Aberrations, Rising and Falling
Edge
Modulation-Current PulseWidth Distortion
OS
PWD
MIN
IMOD = 12mA, TA = +25°C
TYP
±15
IBIAS = 25mA, IMOD = 12mA, 8ns period
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-.
2
_______________________________________________________________________________________
%
100
ps
Single +5V, Fully Integrated,
155Mbps Laser Diode Driver
RBIASSET vs. BIAS CURRENT
RMODSET vs. MODULATION CURRENT
DIFFERENTIAL INPUT
SWING = 1100 mVp-p
10
100,000
5
4
3
RPINSET (Ω)
8
RMODSET (kΩ)
6
10,000
4
2
1000
2
0
20
100
60
40
0
5
IBIAS (mA)
PERCENT CHANGE IN MODULATION
CURRENT vs. TEMPERATURE
8
20
30
25
0
1000
500
MODULATION CURRENT (mAp-p)
MONITOR CURRENT (µA)
PERCENT CHANGE IN BIAS
CURRENT vs. TEMPERATURE
SUPPLY CURRENT
vs. TEMPERATURE
APC DISABLED
6
50
48
4
2
0
-2
-4
-6
SUPPLY CURRENT (mA)
% CHANGE (w.r.t. +25°C)
2
1
0
-1
46
44
42
40
38
36
-8
-10
-2
0
20
60
40
80
34
0
TEMPERATURE (°C)
10
20
30
40
50
60
70
80
20
8
6
ALLOWABLE
RANGE
2
40
MAXIMUM MODULATION CURRENT (mAp-p)
10
60
40
80
TEMPERATURE (°C)
MAXIMUM MODULATION CURRENT
vs. MINIMUM DIFFERENTIAL
INPUT SIGNAL AMPLITUDE
MAX3263-07
12
4
0
TEMPERATURE (°C)
ALLOWABLE ROSADJ RANGE
vs. MODULATION CURRENT
ALLOWABLE ROSADJ (kΩ)
% CHANGE (w.r.t. +25°C)
15
3
MAX3263-04
10
10
MAX3263-05
0
MAX3263-06
1
0
MAX3263-08
RBIASSET (kΩ)
6
MAX3263-03
7
RPINSET vs. MONITOR CURRENT
1,000,000
MAX3263-02
12
MAX3263-01
8
RMODSET = 1.2kΩ
ROSADJ = 2kΩ
35
30
25
20
15
10
5
0
0
0
5
10
15
20
25
MODULATION CURRENT (mAp-p)
30
0
400
800
1200
1600
2000
MINIMUM DIFFERENTIAL
INPUT SIGNAL AMPLITUDE (mVp-p)
_______________________________________________________________________________________
3
MAX3263
__________________________________________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
______________________________________________________________Pin Description
4
PIN
NAME
FUNCTION
1
VREF2
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).
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 2.7kΩ pull-up resistor.
4, 7
GNDB
5
VIN+
Noninverting PECL Data Input
6
VIN-
Inverting PECL Data Input
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.
9
ENB-
Inverting Enable TTL Input. Output currents are enabled only when ENB+ is high and ENB- is low.
10
ENB+
Noninverting Enable TTL Input. Output currents are enabled only when ENB+ is high and
ENB- is low.
11
VREF1
Temperature-Compensated Reference Output. VREF1 is internally connected to VREF2.
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).
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 resistor 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
18
OUT-
Modulation Output. When VIN+ is high and VIN- is low, OUT- sinks IMOD.
20
OUT+
Modulation Output. When VIN+ is low and VIN- is high, OUT+ sinks IMOD.
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.
23
IPIN
24
SLWSTRT
Temperature-Compensated Reference Output. VREF2 is internally connected to VREF1.
Ground for Voltage Reference and Automatic Power-Control Circuitry
Monitor Photodiode Current Input. Connect IPIN to photodiode’s anode.
Slow-Start Capacitor Input. Connect capacitor to ground or leave unconnected to set start-up
time, tSTARTUP = 25.4kΩ (CSLWSTRT + 2pF).
_______________________________________________________________________________________
Single +5V, Fully Integrated,
155Mbps Laser Diode Driver
MAX3263
VCC
OUT+
MAX3263
VIN+
LASER
VINOUT-
VCCA
PHOTODIODE
VCCB
20 x IMODSET
IBIASOUT
GNDA
GNDB
+2.6V
40 x IBIASSET
ENB+
ENB-
BIAS
COMPENSATION
FAILOUT
COMPARATOR
MAIN
BIAS
GENERATOR
IPIN
LOOPSTABILITY
CAPACITOR
0.1µF
VCC x 3/5
SLWSTRT
TRANSCONDUCTANCE
AMPLIFIER
IBIASFB
IBIASSET
IMODSET
IOSADJ
1 x IPINSET
IPINSET
RBIASSET
RMODSET
RPINSET
ROSADJ
VREF1, VREF2
BANDGAP
REFERENCE
Figure 1. Functional Diagram
_______________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-compensated 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) programs 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.
_______________________________________________________________________________________
5
MAX3263
Single +5V, Fully Integrated,
155Mbps Laser Diode Driver
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 output 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 completely 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.
OUTPUTS
VCC
MAX3263
280Ω
280Ω
INPUTS
2(IOSADJ)
9Ω
400Ω
INPUT BUFFER
The APC circuit incorporates the laser diode, the monitor
photodiode, the pin set current mirror, a transconductance 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 photodiode. 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 transconductance 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 amplified 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 output power. This feedback process continues until the
monitor-diode current equals IPINSET.
If the monitor-diode current is sufficiently less than IPINSET (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 monitordiode 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 2.7kΩ to VCC.
The transconductance amplifier can source or sink currents up to approximately 1mA. Since the laser bias generator 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 current slightly higher than required for normal operation.
However, do not exceed the IBIASOUT absolute maximum rating of 75mA.
To maintain APC loop stability, a 0.1µF bypass capacitor may be required across the photodiode. If the APC
function is not used, disconnect the IBIASFB pin.
Enable Inputs
9Ω
2(IOSADJ)
IMOD
The MAX3263 provides complementary enable inputs
(ENB+, ENB-). The laser is disabled by reducing the reference voltage outputs (VREF1, VREF2). Only one logic
state enables laser operation (Figure 3 and Table 1).
OUTPUT STAGE
Figure 2. MAX3263 Modulation Driver (Simplified)
6
_______________________________________________________________________________________
Single +5V, Fully Integrated,
155Mbps Laser Diode Driver
DATA OUT
(LOAD = 1300nm
LASER AT OUT-)
The MAX3263 data inputs accept PECL input signals,
which require 50Ω termination to (VCC - 2V). Figure 4
shows alternative termination techniques. When a termination voltage is not available, use the Theveninequivalent termination. When interfacing with a
non-PECL signal source, use one of the other alternative termination methods shown in Figure 4.
2µs/div
Figure 3. Enable/Disable Operation
Bias Network Compensation
Table 1. MAX3263 Truth Table
ENB-
ENB+
VREF
0
0
Off
0
1
On
1
0
Off
1
1
Off
Temperature Considerations
The MAX3263 output currents are programmed by current mirrors. These mirrors each have a 2VBE temperature
coefficient. The reference voltage (VREF) is adjusted 2VBE
so these changes largely cancel, resulting in output currents 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 damping 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 connections supply the bias-generator and automatic-power
For best laser transmitter performance, add a filter to the
circuit. Most laser packages (TO-46 or DIL) have a significant 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 = 25Ω and C = L / 4R.
Increase C until aberrations are reduced.
The IBIASOUT pin has about 4pF of parasitic capacitance. 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
_______________________________________________________________________________________
7
MAX3263
ENB+
control circuits. For optimum operation, isolate these supplies from each other by independent bypass filtering.
GNDA and GNDB have multiple pins. Connect all pins
to optimize the MAX3263’s high-frequency performance. Ground connections between signal lines
(VIN+, VIN-, OUT+, OUT-) improve the quality of the
signal path by reducing the impedance of the interconnect. Multiple connections, in general, reduce inductance 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 interference.
MAX3263
Single +5V, Fully Integrated,
155Mbps Laser Diode Driver
5V
PECL
SIGNAL SOURCE
5V
82Ω
82Ω
VIN+
120Ω
a) THEVENIN-EQUIVALENT TERMINATION
MAX3263
VIN120Ω
NON-PECL
SIGNAL SOURCE
VIN+
5V
50Ω
50Ω
680Ω
50Ω
1.8k
b) DIFFERENTIAL NON-PECL TERMINATION
MAX3263
50Ω
VIN-
NON-PECL
SIGNAL SOURCE
VIN+
50Ω
180Ω
68Ω
5V
c) SINGLE-ENDED NON-PECL TERMINATION
MAX3263
5V
680Ω
VIN1.8k
5V
ECL
SIGNAL SOURCE
0V
1.3k
1.3k
VIN+
50Ω
d) ECL TERMINATION
3.6k
MAX3263
-2V
THIS SYMBOL REPRESENTS
A TRANSMISSION LINE
WITH CHARACTERISTIC
IMPEDANCE Zo = 50Ω.
VIN50Ω
3.6k
-2V
Figure 4. Alternative PECL Data-Input Terminations
8
_______________________________________________________________________________________
Single +5V, Fully Integrated,
155Mbps Laser Diode Driver
OUT+
≥0.1µF
MAX3263
LASER
PHOTODIODE
IPIN
10µH
25Ω
C
SHUNT RC
IBIASOUT
FERRITE
BEAD
0.01µF
AS CLOSE TO THE
LASER ANODE AS
POSSIBLE
18Ω
AS CLOSE TO THE
LASER CATHODE AS
POSSIBLE
OUT-
Figure 5. Typical Laser Interface with Bias Compensation
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 characteristics:
Wavelength
λ
1300nm
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 η
0.1mW/mA (worst case)
Now assume the communications system has the following requirements:
PAVE
Er
Tr
0dBm (1mW)
6dB (Er = 4)
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 R PINSET 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 equations 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
= 3.9kΩ yields the desired modulation current.
3) Determine the value of ROSADJ:
Using the Allowable R OSADJ Range vs. Modulation
Current graph in the Typical Operating Characteristics,
a 5.6kΩ resistor is chosen for 12mA of modulation current. 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 setting 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 lowest 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 twotimes 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
_______________________________________________________________________________________
9
MAX3263
18Ω
Average Power
Extinction Ratio
Temperature Range
+5V
In this case, set the initial bias value to 34mA (which is
the midpoint of the two extremes). The 40mA adjustment range of the MAX3263 maintains the average
laser power at either extreme.
The Typical Operating Characteristics show that
RBIASSET = 1.8kΩ delivers the required bias current.
Laser Safety and IEC 825
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.
Using the MAX3263 laser driver alone does not ensure
that a transmitter design is compliant with IEC 825 safety requirements. The entire transmitter circuit and component selections must be considered. Each customer
______________________________________________________________________Package Information
SSOP.EPS
MAX3263
Single +5V, Fully Integrated,
155Mbps Laser Diode Driver
10
______________________________________________________________________________________
Single +5V, Fully Integrated,
155Mbps Laser Diode Driver
MAX3263
NOTES
______________________________________________________________________________________
11
MAX3263
Single +5V, Fully Integrated,
155Mbps Laser Diode Driver
NOTES
Maxim makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does Maxim assume any liability 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.
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.
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© 1998 Maxim Integrated Products
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is a registered trademark of Maxim Integrated Products.