19-2081; Rev 1; 12/02 +3.3V, 2.5Gbps Low-Power Laser Driver Features ♦ 30mA Power-Supply Current The MAX3273 accepts differential CML-compatible clock and data input signals. Inputs are self-biased to allow AC-coupling. An input data-retiming latch can be enabled to reject input jitter if a clock signal is available. ♦ Programmable Bias Current from 1mA to 100mA ♦ Single +3.3V Power Supply ♦ Up to 2.7Gbps (NRZ) Operation ♦ Automatic Average Power Control with Failure Monitor ♦ Programmable Modulation Current from 5mA to 60mA ♦ Typical Fall Time of 59ps ♦ Selectable Data Retiming Latch ♦ Complies with ANSI, ITU, and Bellcore SDH/SONET Specifications The driver can provide bias current up to 100mA and modulation current up to 60mAP-P with typical (20% to 80%) edge speeds of 59ps. A failure-monitor output is provided to indicate when the APC loop is unable to maintain average optical power. The MAX3273 is available in a 4mm ✕ 4mm, 24-pin QFN package, as well as in die form. Ordering Information Applications PART TEMP RANGE PIN-PACKAGE MAX3273EGG -40°C to +85°C 24 QFN-EP* (4mm × 4mm) MAX3273E/D -40°C to +85°C Dice** *EP=Exposed pad. SONET OC-48 and SDH STM-16 Transmission Systems **Dice are designed to operate from TA = -40°C to +85°C, but are tested and guaranteed at TA = +25°C only. Add/Drop Multiplexers Digital Cross-Connects Pin Configuration appears at end of data sheet. 2.5Gbps Optical Transmitters Typical Application Circuit VCC 0.01µF LP1 APCFILT2 FAIL APCFILT1 DATA + EN 50Ω LATCH DATA + VCC VCC 25Ω OUT- 100Ω DATA 2.5Gbps SERIALIZER WITH CLOCK GENERATION CLK+ 50Ω LP1 LP2 20Ω DATA OUT+ 25Ω 0.056µF MAX3273 50Ω CLK+ BIAS APCSET CLK- BIASMAX 50Ω MODSET CLK- GND 100Ω MD 500pF REPRESENTS A CONTROLLED-IMPEDANCE TRANSMISSION LINE. †Covered by U.S. patent number 5,883,910. ________________________________________________________________ Maxim Integrated Products 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. 1 MAX3273 † General Description The MAX3273 is a compact, low-power laser driver for applications up to 2.7Gbps. The device uses a single +3.3V supply and typically consumes 30mA. The bias and modulation current levels are programmed by external resistors. An automatic power-control (APC) loop is incorporated to maintain a constant average optical power over temperature and lifetime. The laser driver is fabricated using Maxim’s in-house, secondgeneration SiGe process. MAX3273 +3.3V, 2.5Gbps Low-Power Laser Driver ABSOLUTE MAXIMUM RATINGS Supply Voltage, VCC..............................................-0.5V to +6.0V Current into BIAS, OUT+, OUT- ......................-20mA to +150mA Current into MD.....................................................-5mA to +5mA Voltage at DATA+, DATA-, CLK+, CLK-, LATCH, EN, FAIL..........................-0.5V to (VCC + 0.5V) Voltage at MODSET, BIASMAX, APCSET, APCFILT1, APCFILT2.........................-0.5V to +3.0V Voltage at BIAS .........................................+1.0V to (VCC + 1.5V) Voltage at OUT+, OUT-.............................+1.5V to (VCC + 1.5V) Current into FAIL ...............................................-10mA to +10mA Continuous Power Dissipation (TA = +85°C) 24-Pin QFN (derate 274mW/°C above +85°C) ..........1781mW Storage Temperature Range .............................-55°C to +150°C Operating Junction Temperature ......................-55°C to +150°C Die Attach Temperature (die) ..........................................+400°C Lead Temperature (soldering, 10s) .................................+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 +3.6V, TA = -40°C to +85°C. Typical values are at VCC = +3.3V, IBIAS = 60mA, IMOD = 30mA, TA = +25°C, unless otherwise noted.) (Note 1) PARAMETER Supply Current Bias-Current Range SYMBOL ICC IBIAS CONDITIONS Voltage on BIAS pin (VBIAS) = VCC - 1.6V Bias-Current Stability APC open loop (Note 3) Bias-Current Absolute Accuracy APC open loop (Note 4) MAX UNITS 30 45 mA 100 mA 0.2 mA 1 VID Figure 1 IBIAS = 100mA 61 IBIAS = 1mA 198 -15 0.2 VICM VCC 1.49 TTL Input High Voltage VIH 2.0 TTL Input Low Voltage VIL TTL Output High VOH Sourcing 50µA TTL Output Low VOL Sinking 100µA Common-Mode Input Voltage TYP EN = high (Note 2), VBIAS ≤ 2.6V Bias Off-Current Differential Input Voltage MIN Excluding IBIAS and IMOD VCC 1.32 Monitor-Diode Bias Set Point Stability Monitor-Diode Bias Absolute Accuracy 2 IMD (Note 3) +15 % 1.6 VP-P VCC VID/4 V 0.8 V V 2.4 V 0.4 MD Voltage Monitor Diode DC-Current Range ppm/°C 18 V 1000 µA IMD = 1000µA -480 83 +480 IMD = 18µA -480 159 +480 -15 _______________________________________________________________________________________ V 1.6 +15 ppm/°C % +3.3V, 2.5Gbps Low-Power Laser Driver (VCC = +3.14V to +3.6V, TA = -40°C to +85°C. Typical values are at VCC = +3.3V, IBIAS = 60mA, IMOD = 30mA, TA = +25°C, unless otherwise noted.) (Notes 5, 6) PARAMETER Modulation-Current Range SYMBOL IMOD CONDITIONS (Note 3) MIN TYP 5 EN = high Modulation Off-Current Modulation-Current Stability Modulation-Current Absolute Accuracy MAX UNITS 60 mA 0.2 mA IMOD = 60mA -480 64 +480 IMOD = 5mA -480 34 +480 (Note 4) -15 +15 ppm/°C % Output Current Rise Time tR 20% to 80% (Note 7) 52 87 ps Output Current Fall Time tF 20% to 80% (Note 7) 59 104 ps Output Overshoot/Undershoot δ (Note 7) 15 % APC open loop 364 ns Enable and Startup Delay Maximum Consecutive Identical Digits Pulse-Width Distortion 80 PWD (Notes 7, 8) Random Jitter bits 3 45 ps 1.0 1.5 psRMS Input Latch Setup Time TSU LATCH = high (Figure 1) 75 150 ps Input Latch Hold Time THD LATCH = high (Figure 1) 0 50 ps Specifications at -40°C are guaranteed by design and characterization. Dice are tested at TA= +25°C only. Both the bias and modulation currents are switched off if any of the current set pins is grounded. Guaranteed by design and characterization. Accuracy refers to part-to-part variation. AC characterization was performed by using the circuit in Figure 2. AC characteristics are guaranteed by design and characterization, and measured using a 2.5Gbps 213 - 1 PRBS input data pattern with 80 consecutive zeros and 80 consecutive ones added. Note 7: Measured using a 2.5Gbps repeating 0000 1111 pattern. Note 8: PWD = (wide pulse - narrow pulse) / 2. Note 1: Note 2: Note 3: Note 4: Note 5: Note 6: _______________________________________________________________________________________ 3 MAX3273 AC ELECTRICAL CHARACTERISTICS MAX3273 +3.3V, 2.5Gbps Low-Power Laser Driver CLK+ VIS = 0.1V TO 0.8V CLKTSU THD DATAVIS = 0.1V TO 0.8V DATA+ VID = 0.2V TO 1.6V (DATA+) - (DATA-) 5mA TO 60mA IMOD Figure 1. Required Input Signal and Setup/Hold-Time Definition VCC LP1 = MURATA BLM11HA601SPT LP2 = MURATA BLM21HA102SPT LP3 = COILCRAFT D01607C-333 LP3 LP2 LP2 LP1 LP1 MAX3273 25Ω OUT- OSCILLOSCOPE 0.056µF 50Ω OUT+ 0.056µF VCC 50Ω 50Ω BIAS 15Ω Figure 2. Output Termination for Characterization 4 _______________________________________________________________________________________ +3.3V, 2.5Gbps Low-Power Laser Driver ELECTRICAL EYE DIAGRAM (IMOD = 20mA, 213 - 1 80CID) MAX3273 toc02 MAX3273 toc01 ELECTRICAL EYE DIAGRAM (IMOD = 60mA, 213 - 1 80CID) 400mV/div 125mV/div 60ps/div 60ps/div OPTICAL EYE DIAGRAM (2.488Gbps, 1300nm FP LASER, 1.87GHz FILTER) IMOD vs. RMODSET IBIASMAX vs. RBIASMAX 120 80 70 100 60 IMOD (mA) IBIASMAX (mA) MAX3273 toc05 90 MAX3273 toc04 MAX3273 toc03 140 80 60 50 40 30 40 20 20 10 0 0 0.1 57ps/div MITSUBISHI ML725C8F LASER DIODE 1 10 100 1000 1 100 SUPPLY CURRENT vs. TEMPERATURE 0.8 0.6 0.4 EXCLUDE IBIAS, IMOD 25Ω LOAD 90 80 SUPPLY CURRENT (mA) 1.0 MAX3273 toc07 100 MAX3273 toc06 1.2 10 RMODSET (kΩ) IMD vs. RAPCSET 1.4 IMD (mA) 0.1 RBIASMAX (kΩ) 70 60 50 40 30 20 0.2 10 0 0 0.1 1 10 RAPCSET (kΩ) 100 -40 -15 10 35 60 85 TEMPERATURE (°C) _______________________________________________________________________________________ 5 MAX3273 Typical Operating Characteristics (VCC = 3.3V, TA = +25°C, unless otherwise noted.) Typical Operating Characteristics (continued) (VCC = 3.3V, TA = +25°C, unless otherwise noted.) MAX3273 toc08 50 20 40 PERCENT OF UNITS (%) 15 PWD (ps) IMOD = 60mA MEAN = 52.27ps STDEV = 1.57ps 10 5 0 -5 MAX3273 toc09 TYPICAL DISTRIBUTION OF IMOD RISE TIME PULSE-WIDTH DISTORTION vs. IMOD 25 30 20 10 -10 -15 0 15 25 35 45 55 49.0 50.5 52.0 53.5 55.0 56.5 58.0 59.5 65 RISE TIME (ps) IMOD (mA) TYPICAL DISTRIBUTION OF IMOD FALL TIME TYPICAL DISTRIBUTION OF IMOD FALL TIME IMOD = 5mA MEAN = 63.23ps STDEV = 1.21ps 60 MAX3273 toc10 40 IMOD = 60mA MEAN = 59.41ps STDEV = 1.33ps 50 PERCENT OF UNITS (%) 30 20 40 30 20 10 10 0 0 60 61 62 63 64 65 66 57 67 58 59 60 61 62 63 64 FALL TIME (ps) FALL TIME (ps) PERCENT OF UNITS (%) IMOD = 5mA MEAN = 48.57ps STDEV = 1.48ps MAX3273 toc12 TYPICAL DISTRIBUTION OF IMOD RISE TIME 40 30 20 10 0 45 46 47 48 49 50 51 52 53 RISE TIME (ps) 6 _______________________________________________________________________________________ MAX3273 toc11 5 PERCENT OF UNITS (%) MAX3273 +3.3V, 2.5Gbps Low-Power Laser Driver +3.3V, 2.5Gbps Low-Power Laser Driver PIN NAME 1, 4, 13, 15, 18 VCC FUNCTION 2 DATA+ Noninverting Data Input, with On-Chip Biasing 3 DATA- Inverting Data Input, with On-Chip Biasing 5 CLK+ Noninverting Clock Input for Data Retiming, with On-Chip Biasing Power-Supply Voltage 6 CLK- Inverting Clock Input for Data Retiming, with On-Chip Biasing 7, 9, 12 GND Ground 8 LATCH 10 EN 11 MODSET Data Retiming Enable Input, Active-High. Retiming disabled when floating or pulled low. TTL/CMOS Enable Input. Low for normal operation. Float or pull high to disable laser bias and modulation currents. Internal 100kΩ pullup to VCC. A resistor connected from this pin to ground sets the desired modulation current. 14 BIAS Laser Bias Current Output. Connect to the laser through an inductor. 16 OUT+ Positive Modulation-Current Output. IMOD flows into this pin when input data is high. 17 OUT- Negative Modulation-Current Output. Current flows into this pin when input data is low. Connect to load equivalent to that on OUT+ to maintain differential output balance. 19 MD 20 APCFILT1 A capacitor between APCFILT1 and APCFILT2 sets the dominant pole of the APC feedback loop (CAPCFILT = 0.01µF). Ground APCFILT1 for open-loop operation. 21 APCFILT2 See above. 22 FAIL 23 APCSET A resistor connected from this pin to ground sets the desired average optical power. Connect a 100kΩ resistor to GND for open-loop operation. 24 BIASMAX A resistor connected from this pin to ground sets the maximum bias current. The APC function can subtract current from this maximum value, but cannot add to it. For open-loop operation, this pin sets the laser bias current. EP EXPOSED PAD Ground. Solder this pad to ground. Monitor Diode Input. Connect this pin to the anode of the monitor diode. Leave floating for open-loop operation. TTL/CMOS Failure Output, Active-Low. Indicates APC failure when low. _______________________________________________________________________________________ 7 MAX3273 Pin Description MAX3273 +3.3V, 2.5Gbps Low-Power Laser Driver VCC VCC LATCH LP1 OUT- 0 CD MUX DATA D Q 25Ω OUT+ 1 RD IMOD LP1 CLK IBIAS VCC LP2 MAX3273 BIAS VCC FAILURE DETECTOR EN TIA FAIL MD IMD IAPCSET x160 VBG 500pF x190 MODSET BIASMAX RMODSET RBIASMAX APCFILT1 APCFILT2 APCSET RAPCSET CAPCFILT Figure 3. Functional Diagram Detailed Description The MAX3273 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 jitter of the input signal at speeds as high as 2.7Gbps, the device accepts a differential CML 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. Because the modulation output drives a maximum current of 60mA into the laser with an edge speed of 59ps, large transient voltage spikes can be generated (due to the parasitic inductance of the laser). These transients and the laser-forward voltage leave insuffi8 cient 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 MAX3273’s modulation output is AC-coupled to the cathode of a laser diode. An external pullup inductor is necessary to DCbias the modulation output at VCC. Such a configuration isolates laser-forward voltage from the output circuitry and the supply voltage VCC. A simplified functional diagram is shown in Figure 3. The MAX3273 modulation output is optimized for driving a 25Ω load. Modulation current swings of 75mA are possible, but because of 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 might also be necessary to compensate for the laser-diode parasitic inductance, thereby improving the _______________________________________________________________________________________ +3.3V, 2.5Gbps Low-Power Laser Driver At the data rate of 2.5Gbps, any capacitive load at the cathode of a laser diode degrades the optical output performance. Because the BIAS output is directly connected to the laser cathode, the parasitic capacitance associated with this pin is minimized by using an inductor to isolate the BIAS pin from the laser cathode. Automatic Power Control (APC) To maintain constant average optical power, the MAX3273 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 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 (CAPCFILT). To minimize the pattern-dependent jitter associated with the APC loop-time constant, and to guarantee loop stability, the recommended value for CAPCFILT is 0.01µF. When the APC loop is functioning, the maximum allowable bias current is set by an external resistor, RBIASMAX. An APC failure flag (FAIL) is asserted 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 (see Figure 3). Detailed guidelines for these resistor settings are described in the Design Procedure section. Open-Loop Operation If necessary, the MAX3273 is fully operational without APC. To disable the APC loop, ground the APCFILT1 pin. 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. Output Enable The MAX3273 incorporates a TTL/CMOS input to enable the output. When EN is low, the modulation and bias outputs are enabled. When EN is high or floating, both the bias and modulation currents are off. The typical enable time is 364ns, and the typical disable time is 27ns when the bias is operated open loop. Slow-Start For laser safety reasons, the MAX3273 incorporates a slow-start circuit that provides a delay of 364ns for enabling a laser diode. APC Failure Monitor The MAX3273 provides an APC failure monitor (TTL/CMOS) to indicate an APC loop tracking failure. FAIL is asserted low when the APC loop no longer can regulate the bias current to maintain the desired monitor diode current. FAIL asserts low when the APC loop is disabled. Short-Circuit Protection The MAX3273 provides short-circuit protection for the modulation and bias current sources. If BIASMAX, MODSET, or APCSET is shorted to ground, the bias and modulation output turns off. Design Procedure When designing a laser transmitter, the optical output usually is expressed in terms of average power and extinction ratio. Table 1 gives relationships 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 calculated using Table 1. See the I MOD vs. R MODSET graph in the Typical Operating Characteristics and select the value of RMODSET that corresponds to the required current at +25°C. The equation below provides a derivation of the modulation current using Table 1. Optional Data Input Latch To minimize jitter in the input data, connect a synchronous differential clock signal to the CLK+ and CLKinputs. When the LATCH control input is tied high, the input data is retimed on the rising edge of CLK+. If LATCH is tied low or left floating, the retiming function is disabled and 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. IMOD = 2 × PAVE r −1 × e re + 1 η _______________________________________________________________________________________ 9 MAX3273 optical output ringing and duty-cycle distortion. Refer to Maxim application note HFAN 02.0, Interfacing Maxim Laser Drivers with Laser Diodes, for more information. MAX3273 +3.3V, 2.5Gbps Low-Power Laser Driver Programming the Bias Current with APC Disabled When using the MAX3273 in open-loop operation, the bias current is determined by the RBIASMAX resistor. To select this resistor, see the IBIASMAX vs. RBIASMAX graph in the Typical Operating Characteristics and select the value of RBIASMAX that corresponds to the required IBIASMAX at +25°C. Ground the APCFILT1 pin for openloop operation. Programming the Bias Current with APC Enabled When the MAX3273’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. When using the MAX3273 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 +85°C. 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 (see the Typical Application Circuit). Additionally, the MAX3273 outputs are optimized for a 25Ω load. Therefore, the series combination of RD and RL (where RL represents the laser-diode resistance) should equal 25Ω. Typical values for RD are 18Ω to 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 characteristics of the laser diode and PC board layout, a resistor (RP) of 50Ω to 100Ω in parallel with pullup inductor LP1 can be useful in damping overshoot and ringing in the optical output. In some applications (depending on laser-diode parasitic inductance), an RC-shunt network between the laser cathode and ground helps minimize optical output aberrations. Starting values for most coaxial lasers are R = 75Ω in series with C = 3.3pF. These values should be experimentally adjusted until the optical output waveform is optimized. 10 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 (CAPCFILT), which dominates the APC loop time constant; pullup inductor (LP); and AC-coupling capacitor (CD). To filter out noise effects and guarantee loop stability, the recommended value for CAPCFILT is 0.01µF. This results in an APC loop bandwidth of 100kHz or a time constant of 15µs. As a result, the PDJ associated with an APC loop time constant can be ignored. The time constant associated with the output pullup inductor (LP ≈ LP2) and the AC-coupling capacitor (CD) affects the PDJ. For such a second-order network, the PDJ is dominated by LP because of the low frequency cutoff. For a data rate of 2.5Gbps, the recommended value for CD is 0.056µF. During the maximum CID period, 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 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). To achieve even greater immunity to droop, use an optional third inductor (33µH, LP3 in Figure 2). Input Termination Requirement The MAX3273 data and clock inputs are CML compatible. However, it is not necessary to drive the IC with a standard CML signal. As long as the specified differential voltage swings are met, the MAX3273 operates properly. Calculating Power Consumption The junction temperature of the MAX3273 dice must be kept below +150°C at all times. The total power dissipation of the MAX3273 can be estimated by the following: P = VCC × ICC + (VCC - Vf) ✕ IBIAS + IMOD ✕ (VCC - 25 ✕ IMOD / 2) where I BIAS 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) ✕ 37 (°C/W) ______________________________________________________________________________________ +3.3V, 2.5Gbps Low-Power Laser Driver MAX3273 Table 1. Optical Power Relations PARAMETER SYMBOL RELATION Average Power PAVG PAVG = (P0 + P1) / 2 Extinction Ratio re r e = P1 / P 0 Optical Power of a 1 P1 P1 = 2PAVGre / (re + 1) Optical Power of a 0 P0 P0 = 2PAVG / (re + 1) PP-P PP-P = P1 - P0 = 2PAVG(re - 1) / (re + 1) η η = PP-P / IMOD Modulation Current IMOD IMOD = PP-P / η Threshold Current ITH P0 at 1 ≥ ITH Bias Current IBIAS IBIAS ≥ ITH + IMOD / 2 Laser-to-Monitor Transfer ρMON IMD / PAVG Optical Amplitude Laser Slope Efficiency Note: Assuming a 50% average input duty cycle and mark density. Applications Information An example of how to set up the MAX3273 follows. Select Laser A communication-grade laser should be selected for 2.5Gbps/2.7Gbps applications. Assume the laser output average power is PAVG = 0, 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 = 1310nm • Threshold Current: ITH = 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 RMODSET To achieve a minimum extinction ratio (re) of 6.6 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 1.81mW/ (0.05mW/mA) = 36.2mA. The IMOD vs. RMODSET graph in the Typical Operating Characteristics shows that RMODSET should be 5kΩ. 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 I BIASMAX vs. R BIASMAX graph in the Typical Operating Characteristics shows that RBIASMAX should be 3.5kΩ. 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 7.5kΩ. ______________________________________________________________________________________ 11 MAX3273 +3.3V, 2.5Gbps Low-Power Laser Driver Interface Models Laser Safety and IEC 825 Figures 4 and 5 show simplified input and output circuits for the MAX3273 laser driver. If dice are used, replace package parasitic elements with bondwire parasitic elements. Using the MAX3273 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 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 MAX3273 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 14 mils (350µm). Layout Considerations To minimize inductance, keep the connections between the MAX3273 output pins and laser diode 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. 12 Chip Information TRANSISTOR COUNT: 1672 PROCESS: SiGe ISOLATED SUBSTRATE ______________________________________________________________________________________ +3.3V, 2.5Gbps Low-Power Laser Driver PACKAGE 16kΩ PACKAGE 0.9nH VCC OUT+ 0.9nH 0.1pF IN+ 0.1pF 0.9nH 5kΩ OUT0.1pF VCC 5kΩ 0.9nH IN0.1pF 24kΩ Figure 5. Simplified Output Circuit VCC MD 19 BIAS APCFILT1 20 OUT+ APCFILT2 21 OUT- FAIL 22 VCC APCSET 23 Chip Topography N.C. BIASMAX TOP VIEW 24 Pin Configuration VCC Figure 4. Simplified Input Circuit GND MD GND OUT- APCFILT1 GND 16 OUT+ APCFILT2 MODSET 4 15 VCC 5 14 BIAS VCC 1 18 VCC DATA+ 2 17 DATA- 3 VCC CLK+ 13 FAIL EN 9 10 11 12 BIASMAX EN MODSET GND GND GND N.C. 8 APCSET N.C. LATCH VCC N.C. 7 6 GND GND CLK- MAX3273 GND QFN* 79 mil (2.01mm) LATCH GND N.C. CLK- CLK+ VCC VCC DATA- DATA+ VCC *EXPOSED PAD IS CONNECTED TO GND. 64 mil (1.63mm) ______________________________________________________________________________________ 13 MAX3273 VCC VCC 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.) 12,16,20, 24L QFN.EPS MAX3273 +3.3V, 2.5Gbps Low-Power Laser Driver 14 ______________________________________________________________________________________ +3.3V, 2.5Gbps Low-Power Laser Driver 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 © 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products. MAX3273 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.)