19-4769; Rev 0a; 9/98
KIT
ATION
EVALU
E
L
B
AVAILA
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Automatic Power Control
Features
The MAX3867 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. The synchronizing input latch can be bypassed if
a clock signal is not available.
An automatic power control (APC) feedback loop is
incorporated to maintain a constant average optical
power over temperature and lifetime. The wide modulation current range of 5mA to 60mA and bias current of
1mA to 100mA are easy to program, making this product ideal for use in various SDH/SONET applications.
The MAX3867 also provides enable control, a programmable slow-start circuit to set the laser turn-on delay,
and a failure-monitor output to indicate when the APC
loop is unable to maintain the average optical power.
The MAX3867 is available in a small 48-pin TQFP package as well as dice.
♦ Single +3.3V or +5V Power Supply
♦ 62mA Supply Current at +3.3V
♦ Programmable Modulation Current from
5mA to 60mA
♦ Programmable Bias Current from 1mA to 100mA
♦ Rise/Fall Time < 90ps
♦ Automatic Average Power Control with Failure
Monitor
♦ Complies with ANSI, ITU, and Bellcore
SDH/SONET Specifications
♦ Enable Control
Ordering Information
Applications
SONET/SDH Transmission Systems
Add/Drop Multiplexers
PART
TEMP. RANGE
PIN-PACKAGE
MAX3867ECM
-40°C to +85°C
48 TQFP
MAX3867E/D
-40°C to +85°C
Dice*
*Dice are designed to operate over this range, but are tested and
guaranteed at TA = +25°C only. Contact factory for availability.
Digital Cross-Connects
Section Regenerators
Pin Configuration appears at end of data sheet.
2.5Gbps Optical Transmitters
Typical Operating Circuit
+3.3V
124Ω
FAIL
124Ω
ENABLE
124Ω
LATCH
124Ω
+3.3V
DATA+
LD
*FERRITE
BEAD
OUT-
DATA-
MAX3890
25Ω
20Ω
OUT+
0.056µF
SERIALIZER
WITH
CLOCK GEN.
MAX3867
CLK+
BIAS
CLKCAPC
APCFILT
84.5Ω
APCSET
84.5Ω
MODSET
84.5Ω
BIASMAX
MD
84.5Ω
1000pF
________________________________________________________________ Maxim Integrated Products
1
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.
MAX3867
General Description
MAX3867
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Automatic Power Control
ABSOLUTE MAXIMUM RATINGS
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, SLWSTRT.........-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)
Current into FAIL ...............................................-10mA to +30mA
Continuous Power Dissipation (TA = +85°C)
TQFP (derate 20.8mW/°C above +85°C) ...................1354mW
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, 10sec) .............................+300°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 = +3.14V to +5.5V, TA = -40°C to +85°C. Typical values are at VCC = +3.3V, IMOD = 30mA, IBIAS = 60mA, and TA = +25°C,
unless otherwise noted.) (Note 1)
PARAMETER
Supply Current
Bias Current Range
Bias Off Current
SYMBOL
(Note 2)
IBIAS
(Note 3)
IBIAS-OFF
Bias-Current Stability
Bias-Current Absolute Accuracy
Differential Input Voltage
CONDITIONS
ICC
(Note 5)
VID
Common-Mode Input Voltage
VICM
Clock and Data Input Current
IIN
MIN
TYP
MAX
UNITS
62
105
mA
100
mA
100
µA
1
ENABLE = low (Note 4)
APC open loop, IBIAS = 100mA
230
APC open loop, IBIAS = 1mA
900
APC open loop
-15
15
%
Figure 1
200
1600
mVp-p
VCC VID/4
V
10
µA
PECL compatible
VCC 1.49
VCC 1.32
-1
TTL Input High Voltage
(ENABLE, LATCH)
2.0
V
TTL Input Low Voltage
(ENABLE, LATCH)
TTL Output High Voltage FAIL
Sourcing 50µA
2.4
TTL Output Low Voltage FAIL
Sinking 100µA
0.1
Monitor-Diode Reverse Bias
Voltage
Monitor-Diode DC Current
Range
V
VCC
V
0.44
V
V
18
IMD
(Note 6)
Monitor-Diode Bias Absolute
Accuracy
(Note 5)
2
VCC - 0.3
0.8
1.5
Monitor-Diode Bias Setpoint
Stability
Note 1:
Note 2:
Note 3:
Note 4:
Note 5:
Note 6:
ppm/°C
IMD = 1mA
-480
1000
50
480
90
IMD = 18µA
-15
Characteristics at -40°C guaranteed by design and characterization. Dice are tested at TA = +25°C only.
Tested at RMODSET = 2.49kΩ, RBIASMAX = 1.69kΩ, excluding IBIAS and IMOD.
Voltage on BIAS pin is (VCC - 1.6V).
Both the bias and modulation currents will be switched off if any of the current set pins are grounded.
Accuracy refers to part-to-part variation.
Assuming that the laser to monitor-diode transfer function does not change with temperature.
_______________________________________________________________________________________
15
µA
ppm/°C
%
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Automatic Power Control
(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, and TA =
+25°C.) (Note 7)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Input Latch Setup Time
tSU
LATCH = high, Figure 3
100
ps
Input Latch Hold Time
tH
LATCH = high, Figure 3
100
ps
Modulation-Current Range
Modulation-Off Current
5
IMOD
IMOD-OFF
ENABLE = low (Note 4)
-480
IMOD = 60mA
Modulation-Current Stability
-15
(Note 6)
Output Rise Time
tR
20% to 80% (Note 8)
Output Fall Time
tF
20% to 80% (Note 8)
Output Aberrations
79
MAX3867C/D
69
MAX3867ECM
88
MAX3867C/D
79
Enable/Start-Up Delay
Maximum Consecutive Identical
Digits
Jitter Generation
µA
480
15
MAX3867ECM
(Note 8)
Pulse-Width Distortion
mA
250
IMOD = 5mA
Modulation-Current Absolute
Accuracy
-50
60
200
%
ps
(Note 10)
ps
±15
%
250
ns
80
PWD
ppm/°C
bits
(Notes 8, 9)
9
50
ps
Jitter BW = 12kHz to 20MHz, 0-1 pattern
7
20
psp-p
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.
_______________________________________________________________________________________
3
MAX3867
AC ELECTRICAL CHARACTERISTICS
MAX3867
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Automatic Power Control
DATA+
100mV MIN
DATA-
800mV MAX
200mVp-p MIN
1600mVp-p MAX
(DATA+) - (DATA-)
IOUT+
IMOD
Figure 1. Required Input Signal and Output Polarity
VCC
tCLK = 402ps
A
A
A, B ARE SMD FERRITE BEADS
B = BLM11A601S MURATA ELECTRONICS
A = BLM21A102S MURATA ELECTRONICS
CLK
tSU
B
tH
25Ω
B
MAX3867
DATA
0.056µF
OUT0.5pF
*
OSCILLOSCOPE
OUT+
Figure 3. Setup/Hold Time Definition
0.056µF
BIAS
15Ω
50Ω
50Ω
VCC
* TO COMPENSATE PACKAGE LEADS, NOT USED FOR DIE.
Figure 2. Output Termination for Characterization
4
_______________________________________________________________________________________
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Automatic Power Control
(VCC = +3.3V, load as shown in Figure 2, TA = +25°C, unless otherwise noted.)
DISTRIBUTION OF FALL TIME
(WORST-CASE CONDITIONS)
TYPICAL DISTRIBUTION OF FALL TIME
PERCENT IN UNITS (%)
40
30
20
MEAN = 88ps
σ = 3.0ps
48-TQFP
IMOD = 30mA
VCC = +3.14V
TA = +85°C
35
PERCENT IN UNITS (%)
48-TQFP
IMOD = 30mA
50
40
MAX3867-02a
MAX3867-01
60
30
25
20
15
MEAN = 111.6ps
σ = 2.9ps
10
10
5
0
0
50ps/div
80
84
92
88
96
106 108 110 112 114 116 118 120 122
FALL TIME (ps)
100
FALL TIME (ps)
RANDOM JITTER vs. IMOD
ELECTRICAL EYE DIAGRAM
PATTERN = 213 - 1 + 80 CID
IMOD = 60mA
48-TQFP
PATTERN = 213 - 1 + 80 CID
IMOD = 30mA
48-TQFP
0.020
RANDOM JITTER (UIp-p)
55mV
/div
MAX3867 toc05
0.022
MAX3867-05a
MAX3867-04a
ELECTRICAL EYE DIAGRAM
26mV
/div
MAX3867-03a
EYE DIAGRAM
(2.488Gbps, 1300nm FP LASER,
1.87GHz FILTER, 48-TQFP)
0.018
0.016
0.014
JITTER BW = 12kHz to 20MHz
1-0 PATTERN
0.012
0.010
50ps/div
4
50ps/div
11
18
25
32
39
46
53
60
IMOD (mA)
90
1.1
1.0
0.9
80
70
60
40
60
IMD (mA)
80
50
40
20
0.1
0
1
100
10
RBIASMAX (kΩ)
300
0.6
0.5
0.2
10
0
0.8
0.7
0.4
0.3
30
20
MAX3867-08
1.2
MAX3867-07
MAX3867-06
100
IMOD (mA)
IBIASMAX (mA)
100
IMD vs. RAPCSET
IMOD vs. RMODSET
IBIASMAX vs. RBIASMAX
120
0
1
10
RMODSET (kΩ)
100
0.1
1
10
100
RAPCSET (kΩ)
_______________________________________________________________________________________
5
MAX3867
Typical Operating Characteristics
Typical Operating Characteristics (continued)
(VCC = +3.3V, load as shown in Figure 2, TA = +25°C, unless otherwise noted.)
PULSE-WIDTH DISTORTION
vs. IMOD
SUPPLY CURRENT vs. TEMPERATURE
(EXCLUDE IBIAS, IMOD, 25Ω LOAD)
VCC = +5V
MAX3867-10
90
80
25
MAX3867-09
100
20
70
VCC = +3.3V
60
PWD (ps)
ICC (mA)
MAX3867
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Automatic Power Control
50
40
15
10
VCC = +3.3V
30
VCC = +5V
IMOD = 30mA
IBIAS = 45mA
20
5
10
0.
0
-40
-15
10
35
60
85
5
10
20
30
40
50
60
IMOD (mA)
TEMPERATURE (°C)
Pin Description
6
PIN
NAME
FUNCTION
1, 42, 45
GND2
Ground for internal reference
2, 7, 12, 15, 16,
GND1
Ground for digital circuits
3, 6, 8, 11, 18
VCC1
Power supply for digital circuits
4
DATA+
Positive PECL Data Input
5
DATA-
Negative PECL Data Input
9
CLK+
Positive PECL Clock Input. Connect to VCC if latch function is not used.
10
CLK-
Negative PECL Clock Input. Leave unconnected if latch function is not used.
13
LATCH
14
ENABLE
17
SLWSTRT
19
FAIL
TTL/CMOS output. Indicates APC failure when low.
21, 26, 28, 31, 39,
41, 43
N.C.
No Connection. Leave unconnected.
22
APCFILT
20, 23, 33
GND4
Ground for output circuitry
24, 27, 32
VCC4
Power Supply for output circuitry
TTL/CMOS Latch Input. High for latched data, low for direct data.
TTL/CMOS Enable Input. High for normal operation, low to disable laser bias and modulation
currents.
A capacitor from this pad to ground delays the turn-on time of laser bias and modulation
currents.
Connect a capacitor (CAPCFILT = 0.1µF) from this pad to ground to filter the APC noise.
_______________________________________________________________________________________
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Automatic Power Control
PIN
NAME
FUNCTION
25
BIAS
Laser Bias Current Output
29
OUT+
Positive Modulation-Current Output. IMOD flows through this pad when input data is high.
30
OUT-
Negative Modulation-Current Output. IMOD flows through this pad when input data is low.
35
MD
34, 36, 40
GND3
Ground for APC
37
VCC3
Power Supply for APC
38
CAPC
A capacitor connected from this pad to ground controls the dominant pole of the APC feedback loop. (CAPC = 0.1µF)
44
APCSET
A resistor connected from this pad to ground sets the desired average optical power.
Connect 100kΩ from this pad to ground if APC is not used.
46
MODSET
A resistor connected from this pad to ground sets the desired modulation current.
47
BIASMAX
A resistor connected from this pad to ground sets the maximum bias current. The APC
function can subtract from this maximum value, but can not add to it.
48
VCC2
Monitor Diode Input. Connect this pad to a monitor photodiode anode. A capacitor to ground
is required to filter high-speed AC monitor photocurrent.
Power Supply for internal reference
_______________Detailed Description
The MAX3867 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 MAX3867’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 MAX3867 modulation output is optimized for driving a 25Ω load; the minimum required voltage at OUT+
is 2.0V. Modulation current swings of 80mA are possible, but due to minimum power supply and jitter
requirements at 2.5Gbps, the specified maximum modulation current is limited to 60mA. To interface with the
laser diode, a damping resistor (R D) is required for
impedance matching. An RC shunt network is also necessary to compensate for the laser-diode parasitic
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 connected
to the laser cathode, minimize the parasitic capacitance
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
MAX3867 incorporates an APC loop to compensate for
the changes in laser threshold current over temperature
and lifetime. A back-facet photodiode mounted in the
_______________________________________________________________________________________
7
MAX3867
Pin Description (continued)
MAX3867
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Automatic Power Control
VCC
LATCH
LP
MAX3867
CD
OUT+
IMOD
0
DATA
D
Q
1
RD
MUX
CF
OUT-
CLK
LP
25Ω
RF
VCC
ENABLE
IBIAS
172X
BIAS
40X
5X
MD
1000pF
IMD
FAILURE
DETECTOR
MODSET
BIASMAX
RMODSET
RBIASMAX
CAPC
APCSET
FAIL
CAPC
RAPCSET
Figure 4. Functional Diagram
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 reference current set by RAPCSET. The time constant of
the APC loop is determined by an external capacitor
(CAPC). To eliminate 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 aver8
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 MAX3867 is fully operational without
APC. In this case, the laser current is directly set by two
external resistors connected from ground to BIASMAX
_______________________________________________________________________________________
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Automatic Power Control
Optional Data Input Latch
To minimize input data pattern-dependent jitter, the differential 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 MAX3867 incorporates a laser driver enable function. 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.
Slow-Start
For laser safety reasons, the MAX3867 incorporates a
slow-start circuit which provides a programmable delay
time for enabling a laser diode. An external capacitor
(CSLWSTRT) connected from this pad to ground programs the delay by the equation:
tENABLE ≅ 100kΩ · (CSLWSTRT + 2.5pF)
APC Failure Monitor
The MAX3867 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 MAX3867 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 extinction 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 optical waveform is 50%
Programming the Modulation Current
For a given laser power PAVE, slope efficiency η, and
extinction ration re, the modulation current can be calculated by Table 1. Refer to the IMOD vs. RMODSET 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 MAX3867 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. Refer to 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 MAX3867 in closed-loop operation, the
RBIASMAX resistor sets the maximum bias current available to the laser diode over temperature and life. The
APC loop can subtract from this maximum value but
cannot add to it. Refer to 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 MAX3867’s APC feature is used, program the
average optical power by adjusting the APCSET resistor.
To select this resistor, determine the desired monitor current to be maintained over temperature and life. Refer to
the IMD vs. RAPCSET 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 is required
(Figure 4). If RL represents the laser diode resistance,
the recommended total resistance for RD + RL is 25Ω.
Starting values for coaxial lasers are RF = 75Ω and
C F = 3.3pF. R F and C F should be experimentally
adjusted until the optical output waveform is optimized.
A bypass capacitor should also be placed as close to
the laser anode as possible, for the best performance.
Pattern-Dependent Jitter (PDJ)
When transmitting NRZ data with long strings of consecutive identical digits (CID), LF droop can occur and
contribute to pattern-dependent jitter. To minimize this
Table 1. Optical Power Definition
PARAMETER
Average Power
SYMBOL
PAVE
RELATION
PAVE = (P0 + P1) / 2
Extinction Ratio
re
re = P1 / P0
Optical Power High
P1
P1 = 2PAVE · re / (re + 1)
Optical Power Low
P0
P0 = 2PAVE / (re + 1)
Optical Amplitude
Pp-p
Laser Slope
Efficiency
Modulation Current
η
IMOD
Pp-p = 2PAVE (re - 1) / (re + 1)
η = Pp-p / IMOD
IMOD = Pp-p /η
_______________________________________________________________________________________
9
MAX3867
and MODSET. See the Design Procedure section for
more details on open-loop operation.
MAX3867
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Automatic Power Control
pattern-dependent jitter, 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 pattern-dependent jitter associated with an APC loop time constant can be ignored.
The time constant associated with the output pull-up
inductor (LP), and the AC-coupling capacitor (CD), will
also impact the pattern-dependent jitter. For such a
second-order network, the PDJ due to the low frequency cutoff will be dominated by LP. For a data rate of
2.5Gbps, the recommended value for CD is 0.056µF.
During the maximum CID period t, 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:
-t/τ
12% = 1 - e LP
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 MAX3867 data and clock inputs are PECL-compatible. However, it is not necessary to drive the MAX3867
with a standard PECL signal. As long as the specified
common-mode voltage and the differential voltage
swings are met, the MAX3867 will operate properly.
Calculate Power Consumption
The junction temperature of the MAX3867 dice must be
kept below +150°C at all times. The total power dissipation of the MAX3867 can be estimated by the following:
P = VCC · VCC + (VCC - Vf) · IBIAS
+ IMOD (VCC - 25Ω · IMOD / 2)
where IBIAS is the maximum bias current set by RBIASMAX, IMOD is the modulation current, and Vf is the typical laser forward voltage.
Applications Information
The following is an example of how to set up the
MAX3867.
Select Laser
A communication-grade laser should be selected for
2.488Gbps applications. Assume the laser output average power is PAVE = 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 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 = PAVE · 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 6.6dB over
temperature and lifetime, calculate the required extinction 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.
Determine RBIASMAX
Calculate the maximum threshold current (ITH(MAX)) at
T A = +85°C and end of life. Assuming I TH(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.
Junction temperature = P(W) · 48 (°C/W)
10
______________________________________________________________________________________
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Automatic Power Control
Laser Safety and IEC 825
Using the MAX3867 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, 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.
Wire Bonding Die
For high current density and reliable operation, the
MAX3867 uses gold metalization. Make connections to
the die with gold wire only, using ball-bonding techniques. Wedge bonding is not recommended. Die-pad
size is 4 mils (100µm) square, and die thickness is 12
mils (300µm) mils.
Layout Considerations
To minimize inductance, keep the connections between
the MAX3867 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.
Chip Topography
VCC3
CAPC
N.C.
GND3
N.C.
GND2
CLK- VCC1 VCC1 DATA+ GND1
N.C.
APCSET
GND2
MODSET
VCC2
TOP VIEW
BIASMAX
Pin Configuration
VCC1 CLK+ GND1 DATA- VCC1
48 47 46 45 44 43 42 41 40 39 38 37
GND1
GND2
LATCH
VCC2
GND2
1
36 GND3
GND1
2
35 MD
VCC1
3
34 GND3
DATA+
4
33 GND4
GND1
GND1
SLWSTRT
DATA-
5
32 VCC4
VCC1
VCC1
6
31 N.C.
GND1
7
30 OUT-
FAIL
GND4
VCC1
8
29 OUT+
CLK+
MAX3867
28 N.C.
9
CLK- 10
27 VCC4
VCC1 11
26 N.C.
GND1 12
25 BIAS
VCC4
GND4
APCFILT
N.C.
GND4
FAIL
VCC1
SLWSTRT
GND1
GND1
LATCH
ENABLE
13 14 15 16 17 18 19 20 21 22 23 24
BIASMAX
ENABLE
MODSET
GND2
APCSET
0.083"
N.C.
(2.108mm)
GND2
N.C.
N.C.
GND3
APCFILT
GND4
N.C.
CAPC
VCC4
VCC3
BIAS
GND3
N.C. N.C. OUT- VCCA GND3
VCC4 OUT+ N.C. GND4 MD
0.070"
(1.778mm)
TQFP
______________________________________________________________________________________
11
MAX3867
Modulation Current More than 60mA
At +5V power supply, the headroom voltage for the
MAX3867 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 MAX3867 can also be DC-coupled to a laser diode when operating at +5V supply; the
voltage at OUT+ should be ≥ 2.0V for proper operation.
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Automatic Power Control
TQFPPO.EPS
MAX3867
Package Information
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 or death may occur.
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.
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