General Description
The MAX3669 is a complete, +3.3V laser driver with auto-
matic power control (APC) circuitry for SDH/SONET appli-
cations up to 622Mbps. It accepts differential PECL
inputs, provides bias and modulation currents, and oper-
ates over a temperature range from -40°C to +85°C.
An APC feedback loop is incorporated to maintain a
constant average optical power over temperature and
lifetime. The wide modulation current range from 5mA to
75mA and bias current of 1mA to 80mA are easy to
program, making this product ideal for use in various
SDH/SONET applications. Two pins are provided to
monitor the current levels in the laser: BIASMON with
current proportional to laser bias current, and MODMON
with current proportional to laser modulation.
The MAX3669 also provides enable control and a failure-
monitor output to indicate when the APC loop is unable
to maintain the average optical power. The MAX3669
is available in 4mm x 4mm 24-pin thin QFN and
5mm x 5mm 32-pin TQFP packages.
Applications
622Mbps SDH/SONET Access Nodes
Laser Driver Transmitters
Section Regenerators
Features
♦♦+3.3V or +5.0V Single-Supply Operation
♦♦40mA Supply Current at +3.3V
♦♦Programmable Bias Current from 1mA to 80mA
♦♦Programmable Modulation Current from
5mA to 75mA
♦♦Bias Current and Modulation Current Monitors
♦♦200ps Rise/Fall Time
♦♦Automatic Average Power Control with Failure
Monitor
♦♦Complies with ANSI, ITU, and Bellcore
SONET/SDH Specifications
♦♦Enable Control
+3.3V, 622Mbps SDH/SONET
Laser Driver with Current Monitors and APC
MAX3669
For pricing, delivery, and ordering information, please contact Maxim Direct at
1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.
EVALUATION KIT AVAILABLE
DATA+
BIASMAX
MODSET
APCSET
CAPC
FAIL
ENABLE
GND
MD
BIAS
BIASMON
MODMON
OUT+
0.1μF
LASER
OUT-
CMD
100pF
RFILT
20Ω
CFILT
5pF
CD
1μF
R+
20Ω
R-
6.3Ω
RD
5Ω
FERRITE
BEAD
VCC
DATA-
PECL
+3.3V
+3.3V
+3.3V
84.5Ω
84.5Ω
124Ω
124Ω
4:1
SERIALIZER
WITH
CLOCK GEN
MAX3693
MAX3669
Typical Application Circuit
19-1575; Rev 6; 1/13
Ordering Information
Pin Configurations appear at end of data sheet.
PART TEMP RANGE PIN-PACKAGE
MAX3669ETG -40°C to +85°C 24 TQFN-EP*
MAX3669ETG+ -40°C to +85°C 24 TQFN-EP*
MAX3669EHJ -40°C to +85°C 32 TQFP
MAX3669EHJ+ -40°C to +85°C 32 TQFP
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
+3.3V, 622Mbps SDH/SONET
Laser Driver with Current Monitors and APC
2 Maxim Integrated
MAX3669
ABSOLUTE MAXIMUM RATINGS
DC ELECTRICAL CHARACTERISTICS
(VCC = +3.14V to +5.5V, TA= -40°C to +85°C, unless otherwise noted. Typical values are at VCC = +3.3V, TA= +25°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.
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-, ENABLE,
FAIL, BIASMON, MODMON..................-0.5V to (VCC + 0.5V)
Voltage at OUT+, OUT-.............................+1.5V to (VCC + 1.5V)
Voltage at MODSET, APCSET, BIASMAX, CAPC... -0.5V to +3.0V
Voltage at BIAS .........................................+1.0V to (VCC + 0.5V)
Continuous Power Dissipation (TA= +85°C)
TQFN (derate 20.8mW/°C above +85°C) .................1354mW
TQFP (derate 14.3mW/°C above +85°C)....................929mW
Operating Junction Temperature Range...........-55°C to +150°C
Storage Temperature Range ............................ -65°C to +165°C
Lead Temperature (soldering, 10s) .................................+300°C
MODMON to IMOD Gain AMOD 29 mA/mAIMOD/IMODMON
BIASMON to IBIAS Gain ABIAS 38 mA/mAIBIAS/IBIASMON
35IMD = 18µA (Note 4)
IMD = 1mA
815IBIAS = 1mA
IBIAS = 80mA
PARAMETER SYMBOL MIN TYP MAX UNITS
Common-Mode Input Voltage VICM VCC -V
CC -V
CC -
1.49 1.32 VID/4 V
Differential Input Voltage VID 200 1600 mVP-P
Bias Current Absolute Accuracy -15 +15 %
Bias Current Stability 255 ppm/°C
DATA+, DATA- Input Current IIN -1 +10 µA
Monitor Diode Current Stability -480 -50 +480 ppm/°C
Monitor Diode Current
Absolute Accuracy -15 +15 %
DC Monitor Diode Current IMD 18 1000 µA
Bias Current Range
Supply Current 40 60 mA
IBIAS 180mA
Bias Off Current 100 µA
Monitor Diode Input Voltage
(MD Pin) VMD 0.8 V
TTL Input High Voltage VIH 2 V
TTL Input Low Voltage VIL 0.8 V
TTL Output High Voltage (FAIL)VOH 2.4 VCC - 0.3 VCC V
TTL Output Low Voltage (FAIL)VOL 0.1 0.44 V
CONDITIONS
PECL compatible
Figure 1
APC open loop
APC open loop
(Note 3)
Sourcing 50µA
Sinking 100µA
(Note 1)
VBIAS = VCC - 1.6V
ENABLE = low (Note 2)
+3.3V, 622Mbps SDH/SONET
Laser Driver with Current Monitors and APC
AC ELECTRICAL CHARACTERISTICS
(VCC = +3.14V to +5.5V, load as shown in Figure 2, TA= -40°C to +85°C, unless otherwise noted. Typical values are at VCC = +3.3V,
TA= +25°C.) (Note 5)
Maxim Integrated 3
MAX3669
Note 1: Tested with RMODSET = 5.11kΩ(IMOD ≈38mA), RBIASMAX = 4.56kΩ(IBIAS ≈52mA), excluding IBIAS and IMOD.
Note 2: Both the bias and modulation currents will be disabled if any of the current set pins are shorted to ground.
Note 3: Guaranteed by design and characterization. This assumes that the laser to monitor diode transfer function does not change
with temperature.
Note 4: See the
Typical Operating Characteristics
for worst-case distributions.
Note 5: AC characteristics are guaranteed by design and characterization.
Note 6: Total IMOD out of OUT+. See the
Design Procedure
section for information regarding current delivered to the laser.
Note 7: Input signal is a 622Mbps, 213 - 1 PRBS with eighty inserted 0s.
Note 8: Input signal is a 622Mbps, 11110000 pattern.
Note 9: PWD = (wider pulse – narrower pulse) / 2.
DATA+
DATA-
(DATA+) - (DATA-)
IOUT+
100mV MIN
800mV MAX
200mVP-P
MIN
1600mVP-P
MAX
IMOD
Figure 1. Required Input Signal and Output Polarity
VCC
15Ω
10Ω
1μF
1μF
12.4Ω
20Ω
OUT-
OUT+
BIAS
20Ω
50Ω
OSCILLOSCOPE
MAX3669
VCC
IOUT+
Figure 2. Output Termination for Characterization
10 135IMOD = 75mA
Maximum Consecutive Identical
Digits at 622Mbps CID 80 Bits
IMOD = 5mA
IMOD = 75mA
Jitter Generation (Peak-to-Peak) 100 ps(Note 7)
205IMOD = 5mA (Note 4)
IMOD = 5mA
(Notes 8, 9)
PARAMETER SYMBOL MIN TYP MAX UNITS
230 375 psOutput Rise/Fall Time tR, tF
100 200
Modulation Current Absolute
Accuracy -15 +15 %
Pulse-Width Distortion
(Peak-to-Peak)
70 155 ps
Enable/Start-Up Delay 250 ns
Modulation Current Stability -620 -165 +620 ppm/°C
CONDITIONS
20% to 80%,
RL= 10Ω
||
20Ωload
Open loop
IMOD = 75mA
Modulation Current Range IMOD 575mA(Note 6)
Modulation Off-Current 200 µAENABLE = low (Note 2)
ELECTRICAL EYE DIAGRAM
(IMOD = 35mA)
MAX3669 TOC02
200ps/div
PATTERN = 213 - 1 + 80 CID
IMOD = 35mA
622Mbps DATA RATE
ELECTRICAL EYE DIAGRAM
(IMOD = 75mA)
MAX3669 TOC03
200ps/div
PATTERN = 213 - 1 + 80 CID
IMOD = 75mA
622Mbps DATA RATE
EYE DIAGRAM
(622Mbps, 1300nm LASER
WITH 467MHz FILTER)
MAX3669 TOC01
200ps/div
223 – 1 PRBS
10
0.01
1 10 100
MONITOR DIODE CURRENT
vs. APC SET RESISTOR
0.1
1
MAX3669 TOC04
RAPCSET (kΩ)
IMD (mA)
1000
1
0.1 101 100
BIAS CURRENT
vs. MAXIMUM BIAS SET RESISTOR
10
100
MAX3669 TOC05
RBIASMAX (kΩ)
IBIAS (mA)
100
1
0.1 100 1000
MODULATION CURRENT
vs. MODULATION SET RESISTOR
10
MAX3669 TOC06
RMODSET (kΩ)
IMOD (mA)
101
16
17
19
18
20
21
04020 60 80
RANDOM JITTER
vs. MODULATON CURRENT
MAX3669 TOC07
IMOD (mA)
RANDOM JITTER (psP-P)
INCLUDES RANDOM JITTER
DUE TO MEASUREMENT
EQUIPMENT
-40 10-15 35 60 85
MAX3669 TOC09
TEMPERATURE (°C)
SUPPLY CURRENT (mA)
0
20
10
40
30
50
60
SUPPLY CURRENT
vs. TEMPERATURE
IBIAS = 48mA
IMOD = 27mA
VCC = 5.0V
VCC = 3.3V
+3.3V, 622Mbps SDH/SONET
Laser Driver with Current Monitors and APC
4 Maxim Integrated
MAX3669
Typical Operating Characteristics
(VCC = +3.3V, TA= +25°C, unless otherwise noted.)
+3.3V, 622Mbps SDH/SONET
Laser Driver with Current Monitors and APC
TA = -40°C TO +85°C
IMOD = 5mA
DISTRIBUTION OF MODULATION CURRENT
STABILITY (WORST CASE)
MAX3669-11
MODULATION CURRENT STABILITY (ppm/°C)
UNITS (%)
0
10
5
20
15
30
25
35
-125 75 175-25 275 375 475 575
0
5
15
10
20
25
-100-500 100 300 500
DISTRIBUTION OF MONITOR DIODE CURRENT
STABILITY (WORST CASE)
MAX3669-12
MONITOR DIODE CURRENT STABILITY (ppm/°C)
PERCENT OF UNITS (%)
TA = -40°C TO +85°C
IMD = 18μA
-300
Maxim Integrated 5
MAX3669
Typical Operating Characteristics (continued)
(VCC = +3.3V, TA= +25°C, unless otherwise noted.)
0
10
5
20
15
30
25
35
RATIO OF IMOD vs. IMODMON
MAX3669 toc13
IMOD (mA)
IMOD/IMODMON (mA/mA)
0 20406080
TA = -40°C
TA = +85°C
TA = +25°C
0
10
15
20
25
30
35
40
45
0 20406080
RATIO OF IBIAS vs. IBIASMON
MAX3669 toc14
IBIAS (mA)
IBIAS/IBIASMON (mA/mA)
5
TA = -40°C
TA = +25°C
TA = +85°C
+3.3V, 622Mbps SDH/SONET
Laser Driver with Current Monitors and APC
6 Maxim Integrated
MAX3669
PIN
TQFN-E P TQFP
NAME FUNCTION
1, 13, 16,
19
1, 2, 6, 15,
17, 20, 24 VCC Positive Supply Voltage
2 3 DATA+ Positive PECL Data Input
3 4 DATA- Negative PECL Data Input
4, 8, 11,
17, 22
5, 10, 14,
21, 22, 30 GND Ground
5 7 BIASMON Sink Current Source. Proportional to the laser bias current.
6 8 MODMON Sink Current Source. Proportional to the laser modulation current.
7 9 ENABLE
TTL/CMOS Enable Input. High for normal operation, low to disable laser bias and
modulation currents. Internally pulled high.
9 11 FAIL TTL Output. Indicates APC failure when low. Internally pulled high through a 6k
10 12, 13, 26,
27, 28 N.C. No Connection. Leave unconnected.
12 16 BIAS Laser Bias Current Output. Isolate from laser with a ferrite bead.
14 18 OUT+
Positive Modulation Current Output. IMOD flows into this pad when the input signal is
high. Connect this pad to AC-coupling network.
15 19 OUT-
Negative Modulation Current Output. IMOD flows into this pad when the input signal is
low. Connect this pad to VCC through a 6.3 resistor.
18 23 MD
Monitor Photodiode Connection. Connect this pad to the monitor photodiode anode.
A capacitor to ground is required to filter high-speed AC monitor photocurrent.
20 25 CAPC
APC Compensation Capacitor. A 0.1μF capacitor connected from this pad to ground
controls the dominant pole of the APC feedback loop.
21 29 APCSET
APC Set Resistor. A resistor connected from this pad to ground sets the desired average
optical power. The resulting current is equal to the desired DC monitor diode current.
Connect a 100k resistor from this pad to ground if APC is not used.
23 31 MODSET
Modulation Set Resistor. A resistor from this pad to ground sets the laser modulation
current.
24 32 BIASMAX
Maximum Bias Set Resistor. A resistor from this pad to ground sets the maximum laser
bias current. The APC function can subtract from this maximum value but cannot add to
it. This resistor controls the bias-current level when the APC loop is not used.
— — EP Exposed Pad (TQFN only). The exposed paddle must be soldered to ground.
Pin Description
+3.3V, 622Mbps SDH/SONET
Laser Driver with Current Monitors and APC
Maxim Integrated 7
MAX3669
MAX3669
DATA+
OUT+
OUT-
DATA-
100kΩ
ENABLE
IMOD
VCC
IMD
RAPCSET
RBIASMAX
RBIASMON
RMODMON
RMODSET
APCSET
CAPC
CAPC
BIASMAX
MD
MODSET
FAIL
BIAS
IBIAS
165X
VCC
FAILURE
DETECTOR
40X
5X
VCC IBIAS
38
IMOD
29
Figure 3. Functional Diagram
Detailed Description
The MAX3669 laser driver consists of three main parts:
a high-speed modulation driver, a laser-biasing block
with automatic power control (APC), and bias current
and modulation current monitors. The circuit is opti-
mized for low-voltage (+3.3V) operation.
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 75mA into the laser with a 230ps edge speed, large
transient voltage spikes can be generated due to the
parasitic inductance. These transients and the laser for-
ward 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 MAX3669’s modulation output is designed to be
AC-coupled to the cathode of a laser diode. A simpli-
fied functional diagram is shown in Figure 3.
The MAX3669 modulation output is optimized for driv-
ing a 20Ω⎥⎥ 10Ωload; the minimum required voltage at
OUT+ is 2.0V. Modulation current swings of 75mA are
possible. To interface with the laser diode, a damping
resistor (RD) is required for impedance matching. An
RC shunt network may be used to compensate for the
laser-diode parasitic inductance, thereby improving the
optical output aberrations and duty-cycle distortion.
At a 622Mbps data rate, any capacitive load at the cath-
ode of a laser diode degrades the optical output perfor-
mance. Since the BIAS output is directly connected to the
laser cathode, minimize the parasitic capacitance associ-
ated with this pin by using an inductor to isolate the BIAS
pin from the laser diode.
+3.3V, 622Mbps SDH/SONET
Laser Driver with Current Monitors and APC
8 Maxim Integrated
MAX3669
Automatic Power Control
To maintain constant average optical power, the
MAX3669 incorporates an APC loop to compensate for
the changes in laser threshold current over temperature
and lifetime. A back-facet photodiode mounted in the
laser package is used to convert the optical power into a
photocurrent. The APC loop adjusts the laser bias cur-
rent so the monitor current is matched to a reference cur-
rent set by RAPCSET. The time constant of the APC loop
is determined by an external capacitor (CAPC). To elimi-
nate the pattern-dependent jitter associated with the
APC loop-time constant and to guarantee loop stability,
the recommended value for CAPC is 0.1µF.
When the APC loop is functioning, the maximum allowable
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 average
optical power.
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.
Bias and Modulation Monitors
The MAX3669 includes pins to monitor the output levels
of bias and modulation current. BIASMON and MOD-
MON sink current proportional to laser bias current and
modulation current, respectively. By monitoring the cur-
rent through RMODMON and RBIASMON, it is possible to
monitor the levels of bias and modulation current in the
laser (Figure 3).
Open-Loop Operation
If necessary, the MAX3669 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. Connect a 100kΩresistor from APCSET
to ground and leave MD open for open-loop operation.
Enable Control
The MAX3669 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.
APC Failure Monitor
The MAX3669 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. This output
is internally pulled up to VCC through a 6kΩresistor.
Short-Circuit Protection
The MAX3669 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 outputs 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
average duty cycle of the optical waveform is 50%.
Programming the Modulation Current
In addition to being a function of RMODSET, the modula-
tion current delivered to the laser (IMODL) also depends
on the values of the series damping resistor (RD), the
shunt compensation resistance (RFILT), and the laser
diode’s resistance (see
Typical Operating Circuit
).
The modulation current (assuming CFILT<<CD) into the
laser diode can be represented by the following:
Assuming RD= 5Ωand rLASER = 5Ω, this equation is
simplified to:
IMODL = IMOD(0.67)
For RD= 5.0Ωand a laser resistance of approximately
5Ω, see the Modulation Current vs. Modulation Set
Resistor graph in the
Typical Operating Characteristics
and select the value of RMODSET that corresponds to
the required current at +25°C.
Programming the Bias Current
When using the MAX3669 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 Bias Current vs. Maximum Bias Set
I = I 2
2 + R+ r
MODL MOD D LASER
0
0
Ω
Ω
()
⎡
⎣
⎢
⎢
⎤
⎦
⎥
⎥
Table 1. Optical Power Definition
IMODL = PP-P / ηIMOD
Laser Modulation
Current
η = PP-P / IMODL
η
Laser Slope
Efficiency
PP-P = 2PAVG (re- 1) / (re+ 1)PP-P
Optical Amplitude
P0= 2PAVG / (re+ 1)P0
Optical Power Low
P1= 2PAVG x re/ (re+ 1)P1
Optical Power High
re= P1/ P0
re
Extinction Ratio
PAVG = (P0+ P1) / 2PAVG
Average Power
RELATIONSYMBOLPARAMETER
+3.3V, 622Mbps SDH/SONET
Laser Driver with Current Monitors and APC
Maxim Integrated 9
MAX3669
Resistor graph in the
Typical Operating Character-
istics
and select the value of RBIASMAX that corre-
sponds to the required current at +25°C.
When using the MAX3669 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 Bias Current vs. Maximum
Bias Set Resistor 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 MAX3669’s APC feature is used, program the
average optical power by adjusting the APCSET resis-
tor. To select this resistor, determine the desired moni-
tor current to be maintained over temperature and life.
See the Monitor Diode Current vs. APC Set Resistor
graph in the
Typical Operating Characteristics
and
select the value of RAPCSET that corresponds to the
required current.
Interfacing with the Laser Diode
To minimize optical output aberrations due to the laser
parasitic inductance, an RC shunt network may be
used (see
Typical Operating Circuit
). If RLrepresents
the laser diode resistance, the recommended total
resistance for RD+ RLis 10Ω. Starting values for coaxi-
al lasers are RFILT = 20Ωand CFILT = 5pF. RFILT and
CFILT should be experimentally adjusted to optimize
the output waveform. A bypass capacitor should also
be placed as close to the laser anode as possible for
best performance.
Pattern-Dependent Jitter (PDJ)
When transmitting NRZ data with long strings of consec-
utive identical digits (CIDs), LF droop can contribute to
PDJ. To minimize this PDJ, two external components
must be properly chosen: capacitor CAPC, which domi-
nates the APC loop time constant, 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 20kHz. Consequently, the
PDJ associated with an APC loop time constant can be
ignored.
The time constant associated with the DC blocking
capacitor on IMOD will have an effect on PDJ. It is
important that this time constant produce minimum
droop for long consecutive bit streams.
Referring to Figure 4, the droop resulting from long time
periods without transitions can be represented by the
following equation:
AC-coupling of IMOD results in a discharge level for τ
that is equal to PAVG. An overall droop of 6% relative to
Pp-p equates to a 12% droop relative to PAVG. To
ensure a droop of less than 12% (6% relative to Pp-p),
this equation can be solved for τas follows:
If t1equals 80 consecutive unit intervals without a tran-
sition, the time constant associated with the DC block-
ing capacitor needs to be longer than:
τAC ≥RACCD= 7.8 (80 bits) (1.6ns/bit) = 1.0µs
RFILT can be ignored for CFILT<< CD; therefore, the
estimated value of RAC is:
RAC = 20Ω⏐⏐ (RD+ rLASER)
Assuming RD= 5Ω, and rLASER = 5Ω:
RAC = 6.7Ω
with CD= 1µF, τAC = 6.7µs.
Input Termination Requirement
The MAX3669 data inputs are PECL compatible.
However, it is not necessary to drive the MAX3669 with
a standard PECL signal. As long as the specified com-
mon-mode voltage and differential voltage swings are
met, the MAX3669 will operate properly.
(1 - 0.12)
-t
τ = = 7.8t
ln
(100% - DROOP) = e
-t
τ
DROOP
t
PAVG
Pp-p
τ = ∞
τ << τAC
τAC
t1
Figure 4. Droop
+3.3V, 622Mbps SDH/SONET
Laser Driver with Current Monitors and APC
10 Maxim Integrated
MAX3669
Calculate Power Consumption
The total power dissipation of the MAX3669 can be esti-
mated by the following:
P = VCC xICC + (VCC - Vf) xIBIAS
+ IMOD (VCC - 20ΩxIMOD / 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.
Applications Information
The following is an example of how to set up the
MAX3669.
Select Laser
A communication-grade laser should be selected for
622Mbps applications. Assume the laser output aver-
age power is PAVG = 0dBm, the 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
characteristics:
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 xρMON = 200µA. The Monitor Diode Current
vs. APC Set Resistor graph in the
Typical Operating
Characteristics
shows that RAPCSET should be 6kΩ.
Determine RMODSET
To achieve a minimum extinction ratio (re) of 6.6dB 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 Modulation Current vs.
Modulation Set Resistor graph (see
Typical Operating
Characteristics
) shows that RMODSET should be 5kΩ.
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:
IBIAS = ITH(MAX) + IMOD / 2
In this example, IBIAS = 68.1mA. The Bias Current vs.
Maximum Bias Set Resistor graph in the
Typical
Operating Characteristics
shows that RBIASMAX should
be 3kΩ.
Determine RBIASMON
To avoid saturating the current mirror of BIASMON, the
voltage at this pin should not drop below (VCC - 1.6V).
The resulting condition is:
where IBIASMAX is the maximum current expected for
the application.
Determine RMODMON
To avoid saturating the current mirror of MODMON, the
voltage at this pin should not drop below (VCC - 1V).
The resulting condition is:
Modulation Currents Exceeding 50mA
To drive modulation currents greater than 50mA at
3.3V, external pullup inductors (Figure 5) should be
used to DC-bias the modulation output at VCC. Such a
configuration isolates the laser forward voltage from the
output circuitry and allows the output at OUT+ to swing
above and below the supply voltage VCC.
R 1V A
I
MODMON MOD
MOD
≤⎛
⎝
⎜⎞
⎠
⎟
R 1.6V A
I
BIASMON BIAS
BIASMAX
≤⎛
⎝
⎜⎞
⎠
⎟
LD
RFILT
CFILT
100pF
CD
1μF
RD
5Ω
10Ω
VCC
FERRITE
BEADS
FERRITE BEAD
MD
BIAS
OUT+
OUT-
MAX3669
Figure 5. Output Termination for Maximum Modulation Current
+3.3V, 622Mbps SDH/SONET
Laser Driver with Current Monitors and APC
Maxim Integrated 11
MAX3669
TOP VIEW
MAX3669
TQFP
(5mm x 5mm)
32 28
293031 25
26
27
MODSET
GND
APCSET
N.C.
BIASMAX
N.C.
N.C.
CAPC
10 13 15
14 1611 12
9
ENABLE
FAIL
GND
N.C.
N.C.
VCC
GND
BIAS
17
18
19
20
21
22
23 MD
24 VCC
GND
GND
VCC
OUT-
OUT+
VCC
2
3
4
5
6
7
8MODMON
BIASMON
VCC
GND
DATA-
DATA+
++
VCC
1VCC
24 23 22 21 20 19
BIASMAX
MODSET
GND
APCSET
CAPC
VCC
789101112
ENABLE
GND
N.C.
GND
BIAS
13
14
15
16
17
18
VCC
OUT+
OUT-
VCC
GND
MD
6
5
4
3
2
1
MODMON EP
BIASMON
GND
DATA-
DATA+
VCC
FAIL
THIN QFN
(4mm x 4mm)
MAX3669
At +5V power supply, the headroom voltage for the
MAX3669 is significantly improved. In this case, it is
possible to achieve a modulation current of more than
50mA (using resistor pullups as shown in the
Typical
Operating Circuit
). The MAX3669 can also be DC-coupled
to a laser diode when operating at +5V supply; the volt-
age at OUT+ should be ≥2.0V for proper operation.
Layout Considerations
To minimize inductance, keep the connections between
the MAX3669 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 MAX3669 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. Customers 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 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.
Pin Configurations
+3.3V, 622Mbps SDH/SONET
Laser Driver with Current Monitors and APC
12 Maxim Integrated
MAX3669
Chip Information
SUBSTRATE CONNECTED TO GND
Package Information
For the latest package outline information and land patterns
(footprints), go to www.maximintegrated.com/packages. Note
that a “+”, “#”, or “-” in the package code indicates RoHS status
only. Package drawings may show a different suffix character, but
the drawing pertains to the package regardless of RoHS status.
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND
PATTERN NO.
TQFP H32+2F 21-0110 90-0149
TQFN-EP T2444+3 21-0139 90-0021
MAX3669
+3.3V, 622Mbps SDH/SONET
Laser Driver with Current Monitors and APC
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent
licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and
max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000
13
© 2013 Maxim Integrated Products, Inc. Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
6 1/13
Removed dice option from data sheet; removed the Chip Topography section; added the
Package Information table
1, 2, 3, 11,
12
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