General Description
The MAX3869 is a complete, single +3.3V laser driver
for SDH/SONET applications up to 2.5Gbps. The
device accepts differential PECL data and clock inputs
and provides bias and modulation currents for driving a
laser. A synchronizing input latch can be used (if a
clock signal is available) to reduce jitter.
An automatic power control (APC) feedback loop is
incorporated to maintain a constant average optical
power over temperature and lifetime. The wide modula-
tion current range of 5mA to 60mA and bias current of
1mA to 100mA are easy to program, making this prod-
uct ideal for use in various SDH/SONET applications.
The MAX3869 also provides enable control, two current
monitors that are directly proportional to the laser bias and
modulation currents, and a failure-monitor output to indi-
cate when the APC loop is unable to maintain the average
optical power. The MAX3869 is available in 32-pin TQFP
and small 32-pin QFN packages as well as dice.
Applications
SONET/SDH Transmission Systems
Add/Drop Multiplexers
Digital Cross-Connects
Section Regenerators
2.5Gbps Optical Transmitters
Features
♦Single +3.3V or +5V Power Supply
♦64mA Supply Current at +3.3V
♦Programmable Bias Current from 1mA to 100mA
♦Programmable Modulation Current from
5mA to 60mA
♦Bias Current and Modulation Current Monitors
♦87ps Rise/Fall Time
♦Automatic Average Power Control with Failure
Monitor
♦Complies with ANSI, ITU, and Bellcore
SDH/SONET Specifications
♦Enable Control
*Exposed pad.
**Package Code: G3255-1
***Dice are designed to operate over this range, but are tested and
guaranteed at TA= +25°C only. Contact factory for availability.
+Denotes lead-free package.
Ordering Information
MAX3869
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Current Monitors and APC
________________________________________________________________ Maxim Integrated Products 1
EVALUATION KIT
AVAILABLE
124Ω124Ω
SERIALIZER
WITH
CLOCK GEN.
124Ω
23Ω
LD
25Ω
+3.3V +3.3V
0.056µF
0.01µF
BIASMON
MODMON
+3.3V
1000pF
BIASMAX
LATCH
ENABLE
FAIL
MODSET
APCSET
APCFILT
CLK-
CLK+
DATA-
DATA+
FERRITE
BEAD
OUT+
BIAS
MD
OUT-
CAPC
124Ω
84.5Ω84.5Ω84.5Ω84.5Ω
MAX3869
MAX3890
Typical Application Circuit
19-1570; Rev 4; 1/05
Pin Configuration appears at end of data sheet.
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.
PART TEMP RANGE PIN-PACKAGE
MAX3869EHJ -40°C to +85°C 32 TQFP-EP*
MAX3869EHJ+ -40°C to +85°C 32 TQFP-EP*
MAX3869EGJ -40°C to +85°C 32 QFN**
MAX3869E/D -40°C to +85°C Dice***
MAX3869
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Current Monitors and APC
2 _______________________________________________________________________________________
IMD = 1mA
IMD = 18µA 90
ENABLE = low (Note 4)
APC open loop
(Note 3)
900
(Note 2)
(Note 5)
Sourcing 50µA
ENABLE, LATCH
(Note 6)
ENABLE, LATCH
IBIAS = 100mA
APC open loop
Figure 1
PECL compatible
Sinking 100µA
CONDITIONS
%
-15 15
Monitor-Diode Bias Absolute
Accuracy
ppm/°C
-480 50 480
Monitor-Diode Bias Setpoint
Stability
µA
18 1000
IMD
Monitor-Diode DC Current Range
V
1.5
Monitor-Diode Reverse Bias
Voltage
V
0.1 0.44
TTL Output Low Voltage FAIL
µA
100
IBIAS-OFF
Bias Off-Current
mA
1 100
IBIAS
mA
64 112
ICC
Supply Current
Bias Current Range
V
2.4 VCC - 0.3 VCC
TTL Output High Voltage FAIL
V
0.8
TTL Input Low Voltage
V
2.0
TTL Input High Voltage
µA
-1 10
IIN
Clock and Data Input Current
ppm/°C
230
Bias-Current Stability
%
-15 15
(Note 5)Bias-Current Absolute Accuracy
mVp-p
200 1600
VID
Differential Input Voltage
V
VCC - VCC - VCC -
1.49 1.32 VID/4
VICM
Common-Mode Input Voltage
UNITSMIN TYP MAXSYMBOLPARAMETER
DC ELECTRICAL CHARACTERISTICS
(VCC = +3.14V to +5.5V, TA= -40°C to +85°C. Typical values are at VCC = +3.3V, IMOD = 30mA, IBIAS = 60mA, TA= +25°C, unless
otherwise noted.) (Note 1)
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.
Supply Voltage, VCC............................................. -0.5V to +7.0V
Current into BIAS ...........................................-20mA to +150mA
Current into OUT+, OUT- ................................-20mA to +100mA
Current into MD.....................................................-5mA to +5mA
Voltage at DATA+, DATA-, CLK+, CLK-, ENABLE,
LATCH, FAIL, BIASMON, MODMON .....-0.5V to (VCC + 0.5V)
Voltage at APCFILT, CAPC, MODSET,
BIASMAX, APCSET ...........................................-0.5V to +3.0V
Voltage at OUT+, OUT-.............................+1.5V to (VCC + 1.5V)
Voltage at BIAS .........................................+1.0V to (VCC + 0.5V)
Continuous Power Dissipation (TA= +85°C)
32-Pin TQFP-EP (derate 22.2mW/°C above +85°C) ..1444mW
32-Pin QFN (derate 20.84mW/°C above +85°C) .......1667mW
Storage Temperature Range .............................-65°C to +165°C
Operating Junction Temperature Range...........-55°C to +150°C
Processing Temperature (die) .........................................+400°C
Lead Temperature (soldering, 10s) .................................+300°C
ABSOLUTE MAXIMUM RATINGS
IBIAS/IBIASMON A/A
37
ABIAS
BIASMON to IBIAS Gain
IMOD/IMODMON A/A
29
AMOD
MODMON to IMOD Gain
IBIAS = 1mA
MAX3869
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Current Monitors and APC
_______________________________________________________________________________________ 3
AC ELECTRICAL CHARACTERISTICS
(VCC = +3.14V to +5.5V, load as shown in Figure 2, TA= -40°C to +85°C. Typical values are at VCC = +3.3V, IMOD = 30mA, TA= +25°C.)
(Note 7)
Note 1: Dice are tested at TA= +25°C only.
Note 2: Tested at RMODSET = 2.49kΩ, RBIASMAX = 1.69kΩ, excluding IBIAS and IMOD.
Note 3: Voltage on BIAS pin is (VCC - 1.6V).
Note 4: Both the bias and modulation currents will be switched off if any of the current set pins are grounded.
Note 5: Accuracy refers to part-to-part variation.
Note 6: Assuming that the laser to monitor-diode transfer function does not change with temperature. Guaranteed by design and
characterization.
Note 7: AC characteristics are guaranteed by design and characterization.
Note 8: Measured with 622Mbps 0-1 pattern, LATCH = high.
Note 9: PWD = (wider pulse - narrower pulse) / 2.
Note 10: See Typical Operating Characteristics for worst-case distribution.
IMOD = 5mA 300
78
LATCH = high, Figure 3
LATCH = high, Figure 3
20% to 80% (Note 8)
ps
69
(Note 8)
20% to 80% (Note 8)
ENABLE = low (Note 4)
IMOD = 60mA
(Note 5)
Jitter BW = 12kHz to 20MHz, 0-1 pattern
(Notes 8, 9)
CONDITIONS
tR
Output Rise-Time ps
psp-p
720
Jitter Generation
ps
14 50
PWDPulse-Width Distortion
mA
560
IMOD
Modulation-Current Range
ps
100
tH
ps
100
tSU
Input Latch Setup Time
Input Latch Hold Time
bits
80
Maximum Consecutive Identical
Digits
ns
250
Enable and Start-Up Delay
%
±15
Output Aberrations
79
tF
Output Fall- Time
µA
200
IMOD-OFF
Modulation-Off Current
ppm/°C
-480 -8 480
Modulation-Current Stability
%
-15 15
Modulation-Current Absolute
Accuracy
87 (Note 10)
UNITSMIN TYP MAXSYMBOLPARAMETER
MAX3869EHJ
MAX3869E/D
MAX3869EHJ
MAX3869E/D
DATA+
DATA-
(DATA+) - (DATA-)
IOUT+
100mV MIN
800mV MAX
200mVp-p MIN
1600mVp-p MAX
IMOD
Figure 1. Required Input Signal and Output Polarity
MAX3869
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Current Monitors and APC
4 _______________________________________________________________________________________
CLK
DATA
tCLK = 402ps
tSU tH
Figure 3. Setup/Hold Time Definition
0.056µF
OUT+
BIAS
OUT-
A
B
AA, B ARE SMD FERRITE BEADS:
B = BLM11A601S MURATA ELECTRONICS
A = BLM21A102S MURATA ELECTRONICS
B
VCC
50Ω
15Ω
OSCILLOSCOPE
50Ω
25Ω
0.056µF
VCC
MAX3869
IOUT+
Figure 2. Output Termination for Characterization
Typical Operating Characteristics
(VCC = +3.3V, load as shown in Figure 2, TA= +25°C, unless otherwise noted.)
EYE DIAGRAM
(2.488Gbps, 1300nm FP LASER,
1.87GHz FILTER, 32 TQFP-EP)
MAX3869-01
48ps/div
MITSUBISHI ML725C8F LASER DIODE
0
5
15
10
20
25
84
83 87
32 TQFP-EP
IMOD = 30mA
MEAN = 87.3ps
σ = 1.6ps
88 90
89
8685 91 92
TYPICAL DISTRIBUTION OF FALL TIME
MAX3869-02
FALL TIME (ps)
PERCENT OF UNITS (%)
0
5
20
15
10
30
25
35
114.5
113 119
32 TQFP-EP
IMOD = 60mA
VCC = 3.14V
TA = +85°C
MEAN = 119.1ps
σ = 2.0ps
120.5 123.5
122
117.5116 125 126.5
DISTRIBUTION OF FALL TIME
(WORST-CASE CONDITIONS)
MAX3869-03
FALL TIME (ps)
PERCENT OF UNITS (%)
MAX3869
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Current Monitors and APC
_______________________________________________________________________________________ 5
120
0
110
100 300
IBIASMAX vs. RBIASMAX
MAX3869-07
RBIA
S
MAX
(
kΩ
)
IBIASMAX (mA)
40
80
100
20
60
1.2
0
0.1 1 10 100
IMD vs. RAPCSET
0.4
MAX3869-09
RAP
CS
ET
(
kΩ
)
IMD (mA)
0.6
0.8
1.0
1.1
0.3
0.2
0.1
0.5
0.7
0.9
100
0
1 10 100
IMOD vs. RMODSET
20
10
MAX3869-08
RM
O
D
S
ET
(
kΩ
)
IMOD (mA)
40
30
60
70
50
80
90
0
10
60
50
40
30
20
90
70
80
100
-40 -15 10 35 60 85
SUPPLY CURRENT vs. TEMPERATURE
(EXCLUDE IBIAS, IMOD, 25Ω LOAD)
MAX3869-10
TEMPERATURE (°C)
SUPPLY CURRENT (mA)
VCC = +5.5V
VCC = +3.14V
0
10
30
20
40
50
-40 -15 10 35 60 85
BIAS-CURRENT MONITOR GAIN
vs. TEMPERATURE
MAX3869-11
TEMPERATURE (°C)
GAIN (IBIAS/IBIASMON)
IBIAS = 100mA, IMOD = 50mA
IBIAS = 10mA, IMOD = 10mA
ELECTRICAL EYE DIAGRAM
(IMOD = 30mA, 213-1 +80 CID, 32 TQFP-EP)
MAX3869-04
100ps/div
250mV/div
ELECTRICAL EYE DIAGRAM
(IMOD = 60mA, 213-1 +80 CID, 32 TQFP-EP)
MAX3869-05
100ps/div
400mV/div
3.0
4.0
3.5
5.0
4.5
6.0
5.5
6.5
7.5
7.0
8.0
5 15202510 30 35 40 45 50
RANDOM JITTER vs. IMOD
MAX3869-06
IMOD (mA)
RANDOM JITTER (psp-p)
Typical Operating Characteristics (continued)
(VCC = +3.3V, load as shown in Figure 2, TA= +25°C, unless otherwise noted.)
MAX3869
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Current Monitors and APC
6 _______________________________________________________________________________________
Pin Description
Typical Operating Characteristics (continued)
(VCC = +3.3V, load as shown in Figure 2, TA= +25°C, unless otherwise noted.)
NAME FUNCTION
1, 4, 7 VCC1Power Supply for Digital Circuits
2DATA+ Noninverting PECL Input
PIN
3DATA- Inverting PECL Input
8LATCH TTL/CMOS Latch Input. High for latched data, low for direct data. Internal 100kΩpull-up to VCC.
6CLK- Negative PECL Clock Input. Leave unconnected if latch function is not used.
5CLK+ Positive PECL Clock Input. Connect to VCC if latch function is not used.
14 APCFILT Connect a capacitor (CAPCFILT = 0.1µF) from this pad to ground to filter the APC noise.
12 MODMON Modulation Current Monitor. Sink current source that is proportional to the laser modulation
current.
11 BIASMON Bias Current Monitor. Sink current source that is proportional to the laser bias current.
10, 15 GND1 Ground for Digital Circuits
9ENABLE TTL/CMOS Enable Input. High for normal operation, low to disable laser bias and modulation
current. Internal 100kΩpull-up to VCC.
19 OUT+ Positive Modulation-Current Output. IMOD flows through this pad when input data is high.
16, 18, 21 VCC4 Power Supply for Output Circuitry
17 BIAS Laser Bias Current Output
13 FAIL TTL/CMOS Failure Output. Indicates APC failure when low.
0.
5
15
10
20
25
52010 30 40 50 60
PULSE-WIDTH DISTORTION
vs. IMOD
MAX3869-13
IMOD (mA)
PWD (ps)
VCC = +5V
VCC = +3.3V
0
5
10
15
20
25
30
35
40
-40 -15 10 35 60 85
MODULATION-CURRENT MONITOR GAIN
vs. TEMPERATURE
MAX3869-12
TEMPERATURE (°C)
GAIN (IMOD/IMODMON)
IBIAS = 100mA, IMOD = 50mA
IBIAS = 10mA, IMOD = 10mA
_______________Detailed Description
The MAX3869 laser driver consists of two main parts: a
high-speed modulation driver and a laser-biasing block
with automatic power control (APC). The circuit design
is optimized for both high-speed and low-voltage
(+3.3V) operation. To minimize the pattern-dependent
jitter of the input signal at speeds as high as 2.5Gbps,
the device accepts a differential PECL clock signal for
data retiming. When LATCH is high, the input data is
synchronized by the clock signal. When LATCH is low,
the input data is directly applied to the output stage.
The output stage is composed of a high-speed differential
pair and a programmable modulation current source.
Since the modulation output drives a maximum current
of 60mA into the laser with an edge speed of 100ps,
large transient voltage spikes can be generated (due to
the parasitic inductance). These transients and the
laser forward voltage leave insufficient headroom for
the proper operation of the laser driver if the modulation
output is DC-coupled to the laser diode. To solve this
problem, the MAX3869’s modulation output is designed
to be AC-coupled to the cathode of a laser diode. An
external pull-up inductor is necessary to DC-bias the
modulation output at VCC. Such a configuration isolates
laser forward voltage from the output circuitry and
allows the output at OUT+ to swing above and below
the supply voltage VCC. A simplified functional diagram
is shown in Figure 4.
The MAX3869 modulation output is optimized for driv-
ing a 25Ωload; the minimum required voltage at OUT+
is 2.0V. Modulation current swings of 80mA are possi-
ble, but due to minimum power-supply and jitter
requirements at 2.5Gbps, the specified maximum mod-
ulation current is limited to 60mA. To interface with the
laser diode, a damping resistor (RD) is required for
impedance matching. An RC shunt network may also
be necessary to compensate for the laser-diode para-
sitic inductance, thereby improving the optical output
aberrations and duty-cycle distortion.
At the data rate of 2.5Gbps, any capacitive load at the
cathode of a laser diode will degrade the optical output
performance. Since the BIAS output is directly connect-
ed to the laser cathode, minimize the parasitic capaci-
tance associated with this pin by using an inductor to
isolate the BIAS pin from the laser cathode.
Automatic Power Control
To maintain constant average optical power, the
MAX3869 incorporates an APC loop to compensate for
the changes in laser threshold current over temperature
and lifetime. A back-facet photodiode mounted in the
MAX3869
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Current Monitors and APC
_______________________________________________________________________________________ 7
NAME FUNCTIONPIN
25 VCC3 Power Supply for APC
24 MD Monitor Diode Input. Connect this pad to a monitor photodiode anode. A capacitor to ground
is required to filter high-speed AC monitor photocurrent.
20 OUT- Negative Modulation-Current Output. IMOD flows through this pad when input data is low.
32 VCC2 Power Supply for Internal Reference
31 BIASMAX A resistor connected from this pad to ground sets the maximum bias current. The APC
function can subtract from this maximum value, but cannot add to it.
30 MODSET A resistor connected from this pad to ground sets the desired modulation current.
29 APCSET A resistor connected from this pad to ground sets the desired average optical power.
Connect 100kΩfrom this pad to ground if APC is not used.
26 CAPC A capacitor connected from this pad to ground controls the dominant pole of the APC feed-
back loop (CAPC = 0.1µF).
Pin Description (continued)
22 GND4 Ground for Output Circuitry
23 GND3 Ground for APC
27 GND2 Ground for Internal Reference
28 N.C. No Connection. Leave unconnected.
MAX3869
laser package is used to convert the optical power into
a photocurrent. The APC loop adjusts the laser bias
current so that the monitor current is matched to a ref-
erence current set by RAPCSET. The time constant of
the APC loop is determined by an external capacitor
(CAPC). To eliminate the pattern-dependent jitter asso-
ciated with the APC loop-time constant, and to guaran-
tee loop stability, the recommended value for CAPC is
0.1µF.
When the APC loop is functioning, the maximum allow-
able bias current is set by an external resistor, RBIASMAX.
An APC failure flag (FAIL) is set low when the bias current
can no longer be adjusted to achieve the desired aver-
age optical power. To filter out the APC loop noise, use
an external capacitor at APCFILT with a recommended
value of 0.1µF.
APC closed-loop operation requires the user to set three
currents with external resistors connected between
ground and BIASMAX, MODSET, and APCSET. Detailed
guidelines for these resistor settings are described in
the Design Procedure section.
Open-Loop Operation
If necessary, the MAX3869 is fully operational without
APC. In this case, the laser current is directly set by two
external resistors connected from ground to BIASMAX
and MODSET. See the Design Procedure section for
more details on open-loop operation.
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Current Monitors and APC
8 _______________________________________________________________________________________
LATCH
CD
VCC
1000pF
IMD
RAPCSET
RBIASMAX
RMODSET
APCSET
CAPC
CAPC
BIASMAX
MD
MODSET
FAIL
BIAS
RD
25Ω
IMOD
IBIAS
LP1
VCC
DATA
CLK
ENABLE
BIASMON
MOBMON
OUT+
OUT-
DQ
165x
FAILURE
DETECTOR
40x
5x
29
MAX3869
RP
LP2
IMOD
37
IBIAS
0
MUX
1
Figure 4. Functional Diagram
Optional Data Input Latch
To minimize input data pattern-dependent jitter, the dif-
ferential clock signal should be connected to the data
input latch, which is selected by an external LATCH
control. If LATCH is high, the input data is retimed by
the rising edge of CLK+. If LATCH is low, the input data
is directly connected to the output stage. When this
latch function is not used, connect CLK+ to VCC and
leave CLK- unconnected.
Enable Control
The MAX3869 incorporates a laser driver enable func-
tion. When ENABLE is low, both the bias and modulation
currents are off. The typical laser enable time is 250ns,
and the typical disable time is 25ns.
Current Monitors
The MAX3869 features bias- and modulation-current
monitor outputs. The BIASMON output sinks a current
equal to 1/37 of the laser bias current (IBIAS / 37). The
MODMON output sinks a current equal to 1/29 of the
laser modulation current (IMOD / 29). BIASMON and
MODMON should be connected through a pull-up resis-
tor to VCC. Choose a pull-up resistor value that ensures a
voltage at BIASMON greater than VCC - 1.6V and a volt-
age at MODMON greater than VCC - 1.0V.
Slow-Start
For laser safety reasons, the MAX3869 incorporates a
slow-start circuit that provides a delay of 250ns for
enabling a laser diode.
APC Failure Monitor
The MAX3869 provides an APC failure monitor
(TTL/CMOS) to indicate an APC loop tracking failure.
FAIL is set low when the APC loop can no longer adjust
the bias current to maintain the desired monitor current.
Short-Circuit Protection
The MAX3869 provides short-circuit protection for the
modulation, bias, and monitor current sources. If either
BIASMAX, MODSET, or APCSET is shorted to ground,
the bias and modulation output will be turned off.
Design Procedure
When designing a laser transmitter, the optical output is
usually expressed in terms of average power and extinc-
tion ratio. Table 1 gives the relationships that are helpful
in converting between the optical average power and the
modulation current. These relationships are valid if the
mark density and duty cycle of the optical waveform are
50%.
Programming the Modulation Current
For a given laser power PAVG, slope efficiency (η), and
extinction ration (re), the modulation current can be cal-
culated using Table 1. See the IMOD vs. RMODSET graph
in the Typical Operating Characteristics and select the
value of RMODSET that corresponds to the required cur-
rent at +25°C.
Programming the Bias Current
When using the MAX3869 in open-loop operation, the
bias current is determined by the RBIASMAX resistor. To
select this resistor, determine the required bias current
at +25°C. See the IBIASMAX vs. RBIASMAX graph in the
Typical Operating Characteristics and select the value
of RBIASMAX that corresponds to the required current at
+25°C.
When using the MAX3869 in closed-loop operation, the
RBIASMAX resistor sets the maximum bias current avail-
able to the laser diode over temperature and life. The
APC loop can subtract from this maximum value but
cannot add to it. See the IBIASMAX vs. RBIASMAX graph
in the Typical Operating Characteristics and select the
value of RBIASMAX that corresponds to the end-of-life
bias current at +85°C.
Programming the APC Loop
When the MAX3869’s APC feature is used, program the
average optical power by adjusting the APCSET resistor.
To select this resistor, determine the desired monitor cur-
rent to be maintained over temperature and life. See the
IMD vs. RAPCSET graph in the Typical Operating
Characteristics and select the value of RAPCSET that cor-
responds to the required current.
Interfacing with Laser Diodes
To minimize optical output aberrations caused by signal
reflections at the electrical interface to the laser diode, a
series damping resistor (RD) is required (Figure 4).
Additionally, the MAX3869 outputs are optimized for a
25Ωload. Therefore, the series combination of RDand
RL(where RLrepresents the laser-diode resistance)
MAX3869
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Current Monitors and APC
_______________________________________________________________________________________ 9
PARAMETER SYMBOL RELATION
Average Power PAVG PAVG = (P0+ P1) / 2
Extinction Ratio rere= P1/ P0
Optical Power High P1P1= 2PAVG ·re/ (re+ 1)
Optical Power Low P0P0= 2PAVG / (re+ 1)
Optical Amplitude Pp-p Pp-p = 2PAVG (re- 1) / (re+ 1)
Laser Slope
Efficiency ηη = Pp-p / IMOD
Modulation Current IMOD IMOD = Pp-p / η
Table 1. Optical Power Definition
MAX3869
should equal 25Ω. Typical values for RDare 18Ωto
23Ω. For best performance, a bypass capacitor (0.01µF
typical) should be placed as close as possible to the
anode of the laser diode. Depending on the exact char-
acteristics of the laser diode and PC board layout, a
resistor (RP) of 20Ωto 70Ωin parallel with pull-up induc-
tor LP1 can be useful in damping overshoot and ringing
in the optical output.
In some applications (depending on laser-diode para-
sitic inductance characteristics), an RC shunt network
between the laser cathode and ground will help mini-
mize optical output aberrations. Starting values for most
coaxial lasers are R = 75Ωin series with C = 3.3pF.
These values should be experimentally adjusted until
the optical output waveform is optimized.
Pattern-Dependent Jitter
When transmitting NRZ data with long strings of con-
secutive identical digits (CIDs), LF droop can occur
and contribute to pattern-dependent jitter (PDJ). To
minimize this PDJ, three external components must be
properly chosen: capacitor CAPC, which dominates the
APC loop time constant; pull-up inductor LP; and AC-
coupling capacitor CD.
To filter out noise effects and guarantee loop stability,
the recommended value for CAPC is 0.1µF. This results
in an APC loop bandwidth of 10kHz or a time constant
of 16µs. As a result, the PDJ associated with an APC
loop time constant can be ignored.
The time constant associated with the output pull-up
inductor (LP ≈LP2), and the AC-coupling capacitor (CD)
will also impact the PDJ. For such a second-order net-
work, the PDJ due to the low frequency cutoff will be
dominated by LP. For a data rate of 2.5Gbps, the rec-
ommended value for CDis 0.056µF. During the maxi-
mum CID period,it is recommended to limit the peak
voltage droop to less than 12% of the average (6% of
the amplitude). The time constant can be estimated by:
12% = 1 - e-t/τLP
τLP = 7.8t
If τLP = LP/ 25Ω, and t = 100UI = 40ns, then LP= 7.8µH.
To reduce the physical size of this element (LP), use of
SMD ferrite beads is recommended (Figure 2).
Input Termination Requirement
The MAX3869 data and clock inputs are PECL compat-
ible. However, it is not necessary to drive the MAX3869
with a standard PECL signal. As long as the specified
common-mode voltage and the differential voltage
swings are met, the MAX3869 will operate properly.
Calculating Power Consumption
The junction temperature of the MAX3869 dice must be
kept below +150°C at all times. The total power dissipa-
tion of the MAX3869 can be estimated by the following:
P = VCC ✕ICC + (VCC - Vf) ✕IBIAS
+ IMOD (VCC - 25Ω✕IMOD / 2)
where IBIAS is the maximum bias current set by RBIAS-
MAX, IMOD is the modulation current, and Vfis the typi-
cal laser forward voltage.
Junction Temperature = P(W) ✕45 (°C/W)
___________Applications Information
An example of how to set up the MAX3869 follows.
Select Laser
A communication-grade laser should be selected for
2.488Gbps applications. Assume the laser output aver-
age power is PAVG = 0dBm, minimum extinction ratio is
re= 6.6 (8.2dB), the operating temperature is -40°C to
+85°C, and the laser diode has the following character-
istics:
Wavelength: λ= 1.3µm
Threshold Current: ΙTH = 22mA at +25°C
Threshold Temperature
Coefficient: βTH = 1.3%/°C
Laser to Monitor Transfer: ρMON = 0.2A/W
Laser Slope Efficiency: η= 0.05mW/mA
at +25°C
Determine RAPCSET
The desired monitor diode current is estimated by
IMD = PAVG ·ρMON = 200µA. The IMD vs. RAPCSET
graph in the Typical Operating Characteristics shows
that RAPCSET should be 6.0kΩ.
Determine RMODSET
To achieve a minimum extinction ratio (re) of 6.6 over
temperature and lifetime, calculate the required extinc-
tion ratio at +25°C. Assuming re= 20, the peak-to-peak
optical power Pp-p = 1.81mW, according to Table 1. The
required modulation current is 1.81(mW) / 0.05(mW/mA)
= 36.2mA. The IMOD vs. RMODSET graph in the Typical
Operating Characteristics shows that RMODSET should
be 4.8kΩ.
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Current Monitors and APC
10 ______________________________________________________________________________________
Determine RBIASMAX
Calculate the maximum threshold current (ITH(MAX)) at
TA= +85°C and end of life. Assuming ITH(MAX) =
50mA, the maximum bias current should be:
IBIASMAX = ITH(MAX) + IMOD/2
In this example, IBIASMAX = 68.1mA. The IBIASMAX vs.
RBIASMAX graph in the Typical Operating Characteristics
shows that RBIASMAX should be 3.2kΩ.
Modulation Currents Exceeding 60mA
With a +5V power supply, the headroom voltage for the
MAX3869 is significantly improved. In this case, it is
possible to achieve a modulation current of more than
60mA with AC-coupling, if the junction temperature is
kept below 150°C. The MAX3869 can also be DC-cou-
pled to a laser diode when operating with a +5V sup-
ply; the voltage at OUT+ should be ≥2.0V for proper
operation.
Wire Bonding Die
For high current density and reliable operation, the
MAX3869 uses gold metalization. Make connections to
the die with gold wire only, using ball-bonding tech-
niques. Wedge bonding is not recommended. Die-pad
size is 4 mils (100µm) square, and die thickness is 12
mils (300µm) square.
Layout Considerations
To minimize inductance, keep the connections between
the MAX3869 output pins and LD as close as possible.
Optimize the laser diode performance by placing a
bypass capacitor as close as possible to the laser
anode. Use good high-frequency layout techniques
and multilayer boards with uninterrupted ground planes
to minimize EMI and crosstalk.
Laser Safety and IEC 825
Using the MAX3869 laser driver alone does not ensure
that a transmitter design is compliant with IEC 825. The
entire transmitter circuit and component selections must
be considered. Each customer must determine the level
of fault tolerance required by their application, recogniz-
ing 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 sup-
port 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.
MAX3869
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Current Monitors and APC
______________________________________________________________________________________ 11
Chip Information
TRANSISTOR COUNT: 1561
SUBSTRATE CONNECTED TO GND
MAX3869
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Current Monitors and APC
12 ______________________________________________________________________________________
Pin Configurations Chip Topography
MAX3869
TOP VIEW
32 28
293031 25
26
27
BIASMAX
MODSET
APCSET
N.C.
VCC2
GND2
CAPC
VCC3
10 13 15
14 1611 12
9
ENABLE
BIASMON
GND1
FAIL
MODMON
GND1
APCFILT
VCC4
17
18
19
20
21
22
23 GND3
24 MD
GND4
VCC4
OUT-
OUT+
VCC4
BIAS
2
3
4
5
6
7
8LATCH
VCC1
CLK-
CLK+
VCC1
DATA-
DATA+
1VCC1
TQFP-EP*
*EXPOSED PAD IS CONNECTED TO GND.
LATCH
GND1
VCC1 CLK+ GND1 DATA- VCC1
CLK- VCC1 VCC1 DATA+ GND1
ENABLE
GND1
GND1
BIASMON
MODMON
FAIL
GND4
N.C.
APCFILT
GND4
VCC4
MDGND4N.C.OUT+VCC4
OUT-N.C. N.C. GND3VCC4
BIAS
VCC2
GND2
BIASMAX
MODSET
GND2
APCSET
N.C.
GND3
N.C.
GND3
N.C.
CAPC
VCC3
GND3
0.083"
(2.108mm)
0.070"
(1.778mm)
MAX3869
TOP VIEW
32 28
293031 25
26
27
BIASMAX
MODSET
APCSET
N.C.
VCC2
GND2
CAPC
VCC3
10 13 15
14 1611 12
9
ENABLE
BIASMON
GND1
FAIL
MODMON
GND1
APCFILT
VCC4
17
18
19
20
21
22
23 GND3
24 MD
GND4
VCC4
OUT-
OUT+
VCC4
BIAS
2
3
4
5
6
7
8LATCH
VCC1
CLK-
CLK+
VCC1
DATA-
DATA+
1VCC1
QFN*
*EXPOSED PAD IS CONNECTED TO GND.
MAX3869
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Current Monitors and APC
______________________________________________________________________________________ 13
32L,TQFP.EPS
F
1
2
21-0079
PACKAGE OUTLINE,
32L TQFP, 5x5x1.0mm, EP OPTION
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
F2
2
21-0079
PACKAGE OUTLINE,
32L TQFP, 5x5x1.0mm, EP OPTION
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
MAX3869
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Current Monitors and APC
14 ______________________________________________________________________________________
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 ____________________ 15
© 2005 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products, Inc.
MAX3869
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Current Monitors and APC
32L QFN.EPS
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
