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19-1570; Rev 0; 12/99
KIT ATION EVALU LE B AVAILA
+3.3V, 2.5Gbps SDH/SONET Laser Driver with Current Monitors and APC
General Description Features
o Single +3.3V or +5V Power Supply o 64mA Supply Current at +3.3V o Programmable Bias Current from 1mA to 100mA o Programmable Modulation Current from 5mA to 60mA o Bias Current and Modulation Current Monitors o 87ps Rise/Fall Time o Automatic Average Power Control with Failure Monitor o Complies with ANSI, ITU, and Bellcore SDH/SONET Specifications o Enable Control
MAX3869
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 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 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 indicate when the APC loop is unable to maintain the average optical power. The MAX3869 is available in a small 32-pin TQFP package as well as dice.
Ordering Information
PART MAX3869EHJ MAX3869E/D TEMP. RANGE -40C to +85C -40C to +85C PIN-PACKAGE 32 TQFP-EP* Dice**
Applications
SONET/SDH Transmission Systems Add/Drop Multiplexers Digital Cross-Connects Section Regenerators 2.5Gbps Optical Transmitters
*EP = Exposed Paddle. **Dice are designed to operate over this range, but are tested and guaranteed at TA = +25C only. Contact factory for availability. Pin Configuration appears at end of data sheet.
Typical Application Circuit
+3.3V ENABLE LATCH +3.3V FAIL 0.01F LD FERRITE BEAD 23 0.056F SERIALIZER WITH CLOCK GEN. 84.5 84.5 84.5 84.5 CLK+ CLKMD BIASMAX MODSET APCFILT APCSET BIASMON CAPC MODMON 1000pF MAX3869 BIAS
124
124
124
124 DATA+
25
OUTOUT+
MAX3890
DATA-
+3.3V
________________________________________________________________ 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.
+3.3V, 2.5Gbps SDH/SONET Laser Driver with Current Monitors and APC MAX3869
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, 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 = +85C) 32-Pin TQFP-EP (derate 22.2mW/C above +85C) ..1444mW Storage Temperature Range .............................-65C to +165C Operating Junction Temperature Range ...........-55C to +150C Processing Temperature (die) .........................................+400C Lead Temperature (soldering, 10s) .................................+300C
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 = -40C to +85C. Typical values are at VCC = +3.3V, IMOD = 30mA, IBIAS = 60mA, TA = +25C, unless otherwise noted.) (Note 1) PARAMETER Supply Current Bias Current Range Bias Off-Current Bias-Current Stability Bias-Current Absolute Accuracy Differential Input Voltage Common-Mode Input Voltage Clock and Data Input Current TTL Input High Voltage TTL Input Low Voltage TTL Output High Voltage FAIL TTL Output Low Voltage FAIL Monitor-Diode Reverse Bias Voltage Monitor-Diode DC Current Range Monitor-Diode Bias Setpoint Stability Monitor-Diode Bias Absolute Accuracy BIASMON to IBIAS Gain MODMON to IMOD Gain ABIAS AMOD IMD (Note 6) (Note 5) IBIAS/IBIASMON IMOD/IMODMON IMD = 1mA IMD = 18A -15 37 29 (Note 5) VID VICM IIN ENABLE, LATCH ENABLE, LATCH Sourcing 50A Sinking 100A 2.4 0.1 1.5 18 -480 50 90 15 1000 480 VCC - 0.3 SYMBOL ICC IBIAS IBIAS-OFF (Note 2) (Note 3) ENABLE = low (Note 4) APC open loop APC open loop Figure 1 PECL compatible IBIAS = 100mA IBIAS = 1mA -15 200 VCC 1.49 -1 2.0 0.8 VCC 0.44 VCC 1.32 230 900 15 1600 VCC VID/4 10 1 CONDITIONS MIN TYP 64 MAX 112 100 100 UNITS mA mA A ppm/C % mVp-p V A V V V V V A ppm/C % A/A A/A
2
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+3.3V, 2.5Gbps 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 = -40C to +85C. Typical values are at VCC = +3.3V, IMOD = 30mA, TA = +25C.) (Note 7) PARAMETER Input Latch Setup Time Input Latch Hold Time Modulation-Current Range Modulation-Off Current Modulation-Current Stability Modulation-Current Absolute Accuracy Output Rise Time Output Fall Time Output Aberrations Enable/Start-Up Delay Maximum Consecutive Identical Digits Pulse-Width Distortion Jitter Generation Note 1: Note 2: Note 3: Note 4: Note 5: Note 6: PWD (Notes 8, 9) Jitter BW = 12kHz to 20MHz, 0-1 pattern 80 14 7 50 20 tR tF SYMBOL tSU tH IMOD IMOD-OFF ENABLE = low (Note 4) IMOD = 60mA IMOD = 5mA (Note 5) 20% to 80% (Note 8) 20% to 80% (Note 8) (Note 8) MAX3869EHJ MAX3869E/D MAX3869EHJ MAX3869E/D -15 78 69 87 79 15 250 (Note 10) -480 -8 300 15 CONDITIONS LATCH = high, Figure 3 LATCH = high, Figure 3 MIN 100 100 5 60 200 480 TYP MAX UNITS ps ps mA A ppm/C % ps ps % ns bits ps psp-p
MAX3869
Dice are tested at TA = +25C only. Tested at RMODSET = 2.49k, RBIASMAX = 1.69k, 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. 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.
DATA+ DATA-
100mV MIN 800mV MAX
200mVp-p MIN (DATA+) - (DATA-) 1600mVp-p MAX
IOUT+ IMOD
Figure 1. Required Input Signal and Output Polarity _______________________________________________________________________________________ 3
+3.3V, 2.5Gbps SDH/SONET Laser Driver with Current Monitors and APC MAX3869
VCC
tCLK = 402ps
A A A, B ARE SMD FERRITE BEADS: B = BLM11A601S MURATA ELECTRONICS A = BLM21A102S MURATA ELECTRONICS
CLK
tSU
tH
B
B 0.056F
25
DATA
MAX3869
OUTIOUT+ OUT+ 0.056F BIAS 15 50 50
OSCILLOSCOPE
Figure 3. Setup/Hold Time Definition
VCC
Figure 2. Output Termination for Characterization
Typical Operating Characteristics
(VCC = +3.3V, load as shown in Figure 2, TA = +25C, unless otherwise noted.)
EYE DIAGRAM (2.488Gbps, 1300nm FP LASER, 1.87GHz FILTER, 32 TQFP-EP)
MAX3869-01
TYPICAL DISTRIBUTION OF FALL TIME
MAX3869-02
DISTRIBUTION OF FALL TIME (WORST-CASE CONDITIONS)
32 TQFP-EP IMOD = 60mA VCC = 3.14V TA = +85C
MAX3869-03
25 32 TQFP-EP IMOD = 30mA 20 PERCENT OF UNITS (%)
35 30 PERCENT OF UNITS (%) 25 20 15 10 5 MEAN = 119.1ps = 2.0ps
15 MEAN = 87.3ps = 1.6ps
10
5
0 48ps/div MITSUBISHI ML725C8F LASER DIODE 83 84 85 86 87 88 89 FALL TIME (ps) 90 91 92
0 113 114.5 116 117.5 119 120.5 122 123.5 125 126.5 FALL TIME (ps)
4
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+3.3V, 2.5Gbps SDH/SONET Laser Driver with Current Monitors and APC MAX3869
Typical Operating Characteristics (continued)
(VCC = +3.3V, load as shown in Figure 2, TA = +25C, unless otherwise noted.)
ELECTRICAL EYE DIAGRAM (IMOD = 30mA, 213-1 +80 CID, 32 TQFP-EP)
MAX3869-04
ELECTRICAL EYE DIAGRAM (IMOD = 60mA, 213-1 +80 CID, 32 TQFP-EP)
MAX3869-05
RANDOM JITTER vs. IMOD
7.5 7.0 RANDOM JITTER (psp-p) 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 5 10 15 20 25 30 35 40 45 50
MAX3869-06
8.0
250mV/div
100ps/div
400mV/div
100ps/div
IMOD (mA)
IBIASMAX vs. RBIASMAX
MAX3869-07
IMOD vs. RMODSET
MAX3869-08
IMD vs. RAPCSET
1.1 1.0 0.9 IMD (mA) 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
MAX3869-09
120 100 80 60 40 20 0 1 10 RBIASMAX (k) 100
100 90 80 70 IMOD (mA) 60 50 40 30 20 10 0
1.2
IBIASMAX (mA)
300
1
10 RMODSET (k)
100
0.1
1 RAPCSET (k)
10
100
SUPPLY CURRENT vs. TEMPERATURE (EXCLUDE IBIAS, IMOD, 25 LOAD)
MAX3869-10
BIAS-CURRENT MONITOR GAIN vs. TEMPERATURE
MAX3869-11
100 90 80 SUPPLY CURRENT (mA) 70 60 50 40 30 20 10 0 -40 -15 10 35 60 VCC = +3.14V VCC = +5.5V
50 IBIAS = 100mA, IMOD = 50mA IBIAS = 10mA, IMOD = 10mA 30
40 GAIN (IBIAS/IBIASMON) 85
20
10
0 -40 -15 10 35 60 85 TEMPERATURE (C) TEMPERATURE (C)
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+3.3V, 2.5Gbps SDH/SONET Laser Driver with Current Monitors and APC MAX3869
Typical Operating Characteristics (continued)
(VCC = +3.3V, load as shown in Figure 2, TA = +25C, unless otherwise noted.)
MODULATION-CURRENT MONITOR GAIN vs. TEMPERATURE
MAX3869-12
PULSE-WIDTH DISTORTION vs. IMOD
MAX3869-13
40 35 GAIN (IMOD/IMODMON) 30 25 20 15 10 5 0 -40 -15 10 35 60 IBIAS = 100mA, IMOD = 50mA IBIAS = 10mA, IMOD = 10mA
25
20 VCC = +3.3V PWD (ps) 15
10 VCC = +5V 5
0. 85 5 10 20 30 IMOD (mA) 40 50 60 TEMPERATURE (C)
Pin Description
PIN 1, 4, 7 2 3 5 6 8 9 10, 15 11 12 13 14 16, 18, 21 17 19 NAME VCC1 DATA+ DATACLK+ CLKLATCH ENABLE GND1 BIASMON MODMON FAIL APCFILT VCC4 BIAS OUT+ Power Supply for Digital Circuits Noninverting PECL Input Inverting PECL Input Positive PECL Clock Input. Connect to VCC if latch function is not used. Negative PECL Clock Input. Leave unconnected if latch function is not used. TTL/CMOS Latch Input. High for latched data, low for direct data. Internal 100k pull-up to VCC. TTL/CMOS Enable Input. High for normal operation, low to disable laser bias and modulation current. Internal 100k pull-up to VCC. Ground for Digital Circuits Bias Current Monitor. Sink current source that is proportional to the laser bias current. Modulation Current Monitor. Sink current source that is proportional to the laser modulation current. TTL/CMOS Failure Output. Indicates APC failure when low. Connect a capacitor (CAPCFILT = 0.1F) from this pad to ground to filter the APC noise. Power Supply for Output Circuitry Laser Bias Current Output Positive Modulation-Current Output. IMOD flows through this pad when input data is high. FUNCTION
6
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+3.3V, 2.5Gbps SDH/SONET Laser Driver with Current Monitors and APC
Pin Description (continued)
PIN 20 22 23 24 25 26 27 28 29 30 31 32 NAME OUTGND4 GND3 MD VCC3 CAPC GND2 N.C. APCSET MODSET BIASMAX VCC2 FUNCTION Negative Modulation-Current Output. IMOD flows through this pad when input data is low. Ground for Output Circuitry Ground for APC 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 APC A capacitor connected from this pad to ground controls the dominant pole of the APC feedback loop (CAPC = 0.1F). Ground for Internal Reference No Connection. Leave unconnected. A resistor connected from this pad to ground sets the desired average optical power. Connect 100k from this pad to ground if APC is not used. A resistor connected from this pad to ground sets the desired modulation current. 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. Power Supply for Internal Reference
MAX3869
_______________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 driving a 25 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 (RD) is required for impedance matching. An RC shunt network may also be 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 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
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+3.3V, 2.5Gbps SDH/SONET Laser Driver with Current Monitors and APC MAX3869
VCC
LATCH
LP2
LP1
RP RD CD
MAX3869
OUT+ 0 MUX DATA CLK 25 VCC ENABLE BIASMON IBIAS BIAS D Q 1 OUTIMOD
IBIAS 37
165x 5x
40x
MOBMON
MD 1000pF IMOD 29 IMD FAILURE DETECTOR
MODSET RMODSET
BIASMAX FAIL RBIASMAX
CAPC CAPC
APCSET 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 0.1F. 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. To filter out the APC loop noise, use
8
an external capacitor at APCFILT with a recommended value of 0.1F. 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.
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+3.3V, 2.5Gbps SDH/SONET Laser Driver with Current Monitors and APC
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. For a given laser power PAVG, slope efficiency , and extinction ration re, the modulation current can be calculated 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 current at +25C.
Programming the Modulation Current
MAX3869
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 +25C. See the IBIASMAX vs. RBIASMAX graph in the Typical Operating Characteristics and select the value of RBIASMAX that corresponds to the required current at +25C. When using the MAX3869 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. 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 +85C.
Enable Control
The MAX3869 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.
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 resistor to VCC. Choose a pull-up resistor value that ensures a voltage at BIASMON greater than VCC - 1.6V and a voltage at MODMON greater than VCC - 1.0V.
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 current to be maintained over temperature and life. See the I MD vs. R APCSET graph in the Typical Operating Characteristics and select the value of RAPCSET that corresponds to the required current.
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.
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 25 load. Therefore, the series combination of RD and RL (where RL represents the laser-diode resistance)
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 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 mark density and duty cycle of the optical waveform are 50%.
Table 1. Optical Power Definition
PARAMETER Average Power Extinction Ratio Optical Power High Optical Power Low Optical Amplitude Laser Slope Efficiency Modulation Current SYMBOL PAVG re P1 P0 Pp-p IMOD RELATION PAVG = (P0 + P1) / 2 re = P1 / P0 P1 = 2PAVG * re / (re + 1) P0 = 2PAVG / (re + 1) Pp-p = 2PAVG (re - 1) / (re + 1) = Pp-p / IMOD IMOD = Pp-p / 9
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+3.3V, 2.5Gbps SDH/SONET Laser Driver with Current Monitors and APC
should equal 25. Typical values for RD are 18 to 23. For best performance, a bypass capacitor (0.01F typical) should be placed as close as possible to the anode of the laser diode. Depending on the exact characteristics of the laser diode and PC board layout, a resistor (RP) of 20 to 70 in parallel with pull-up inductor LP1 can be useful in damping overshoot and ringing in the optical output. In some applications (depending on laser-diode parasitic inductance characteristics), an RC shunt network between the laser cathode and ground will help minimize optical output aberrations. Starting values for most coaxial lasers are R = 75 in series with C = 3.3pF. These values should be experimentally adjusted until the optical output waveform is optimized.
MAX3869
Calculating Power Consumption
The junction temperature of the MAX3869 dice must be kept below +150C at all times. The total power dissipation of the MAX3869 can be estimated by the following: P = VCC * ICC + (VCC - Vf) * IBIAS + IMOD (VCC - 25 * 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. Junction Temperature = P(W) * 45 (C/W)
___________Applications Information
An example of how to set up the MAX3869 follows.
Pattern-Dependent Jitter
When transmitting NRZ data with long strings of consecutive 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 ACcoupling capacitor CD. To filter out noise effects and guarantee loop stability, the recommended value for CAPC is 0.1F. This results in an APC loop bandwidth of 10kHz or a time constant of 16s. 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 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 0.056F. 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/ 12% = 1 - e LP If LP = LP / 25, and t = 100UI = 40ns, then LP = 7.8H. To reduce the physical size of this element (LP), use of SMD ferrite beads is recommended (Figure 2).
Select Laser
A communication-grade laser should be selected for 2.488Gbps applications. Assume the laser output average power is PAVG = 0dBm, minimum extinction ratio is re = 6.6 (8.2dB), the operating temperature is -40C to +85C, and the laser diode has the following characteristics: Wavelength: = 1.3m Threshold Current: Threshold Temperature Coefficient: Laser to Monitor Transfer: Laser Slope Efficiency: TH = 22mA at +25C TH = 1.3%/C MON = 0.2A/W = 0.05mW/mA at +25C
Determine RAPCSET
The desired monitor diode current is estimated by IMD = PAVG * MON = 200A. The IMD vs. RAPCSET graph in the Typical Operating Characteristics shows that RAPCSET should be 6.0k.
Determine RMODSET
To achieve a minimum extinction ratio (re) of 6.6dB over temperature and lifetime, calculate the required extinction ratio at +25C. 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 4.8k.
LP = 7.8t
Input Termination Requirement
The MAX3869 data and clock inputs are PECL compatible. 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.
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+3.3V, 2.5Gbps SDH/SONET Laser Driver with Current Monitors and APC
Determine RBIASMAX
Calculate the maximum threshold current (ITH(MAX)) at T A = +85C 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 3.2k.
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.
MAX3869
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 150C. The MAX3869 can also be DC-coupled to a laser diode when operating with a +5V supply; the voltage at OUT+ should be 2.0V for proper operation.
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, 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 MAX3869 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 (100m) square, and die thickness is 12 mils (300m) square.
Chip Information
TRANSISTOR COUNT: 1561 SUBSTRATE CONNECTED TO GND
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11
+3.3V, 2.5Gbps SDH/SONET Laser Driver with Current Monitors and APC MAX3869
Pin Configuration
CLK-
Chip Topography
VCC1 VCC1 DATA+ GND1 VCC1 CLK+ GND1 DATA- VCC1 GND2 VCC2 BIASMAX MODSET GND2 APCSET N.C. 0.083" GND3 (2.108mm) N.C. GND3 N.C. CAPC VCC3 GND3
TOP VIEW
BIASMAX MODSET APCSET CAPC GND2 VCC2 VCC3 N.C.
GND1 LATCH
32 VCC1 DATA+ DATAVCC1 CLK+ CLKVCC1 LATCH 1 2 3 4 5 6 7 8 9 ENABLE
31
30
29
28
27
26
25 24 MD 23 GND3 22 GND4 21 VCC4
ENABLE GND1 GND1 BIASMON MODMON FAIL GND4 N.C. APCFILT GND4 VCC4 BIAS
MAX3869
20 OUT19 OUT+ 18 VCC4 17 BIAS
10 GND1
11 BIASMON
12 MODMON
13 FAIL
14 APCFILT
15 GND1
16
N.C. N.C. OUT- VCC4 GND3 VCC4 OUT+ N.C. GND4 MD 0.070" (1.778mm)
12
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VCC4
+3.3V, 2.5Gbps SDH/SONET Laser Driver with Current Monitors and APC
Package Information
32L,TQFP.EPS
MAX3869
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+3.3V, 2.5Gbps SDH/SONET Laser Driver with Current Monitors and APC MAX3869
Package Information (continued)
14
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+3.3V, 2.5Gbps SDH/SONET Laser Driver with Current Monitors and APC MAX3869
NOTES
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+3.3V, 2.5Gbps SDH/SONET Laser Driver with Current Monitors and APC MAX3869
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 or death may occur.
16 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 1999 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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