19-2597; Rev 1; 5/04 3.2Gbps Compact SFP VCSEL Driver The MAX3741 is a high-speed VCSEL driver for smallform-factor (SFF) and small-form-factor pluggable (SFP) fiber-optic LAN transmitters. It contains a bias generator, laser modulator, and peaking current option to improve VCSEL edge speed. The driver accommodates common cathode and differential configurations. The MAX3741 operates up to 3.2Gbps. It can switch up to 15mA of laser modulation current and source up to 15mA of bias current. The MAX3741 is designed to interface with a digital potentiometer and control circuitry. The MAX3741 accommodates various VCSEL packages, including low-cost TO-46 headers. The MAX3741 is available in a compact 3mm x 3mm 16-pin thin QFN package and operates over a temperature range of -40°C to +85°C. Features ♦ 2mA to 15mA Modulation Current ♦ 1mA to 15mA Bias Current ♦ Optional Peaking Current to Improve VCSEL Edge Speed ♦ Supports Common Cathode and Differential Configuration ♦ 3mm × 3mm 16-Pin Thin QFN Package Applications Ordering Information Multirate (1Gbps to 3.2Gbps) SFP/SFF Modules Gigabit Ethernet Optical Transmitters Fibre Channel Optical Transmitters PART TEMP RANGE PINPACKAGE PKG. CODE MAX3741ETE -40°C to +85°C 16 Thin QFN T1633F-3 Pin Configuration Typical Application Circuit +3.3V 0.1µF L1* IN+ TX_DISABLE 1 IN+ 2 BIASSET BIAS BIAS VCC TOP VIEW VCC GND 0.01µF 16 15 14 13 12 BIASMON 0.01µF 11 OUT+ MAX3741 3mm x 3mm 0.01µF OUT50Ω BIASMON BIASSET RBIASSET MODSET RMODSET GND PEAKSET RPEAKSET 3 N.C. 4 5 RMON 10 OUT9 VCC TX_DISABLE IN- 6 7 8 GND OUT+ PEAKSET MAX3741 MODSET IN0.1µF VCC THIN QFN EXPOSED PAD IS CONNECTED TO GND. THIS SYMBOL REPRESENTS A TRANSMISSION LINE OF CHARACTERISTIC IMPEDANCE Zo = 50Ω. * FERRITE BEAD, MURATA BLM18HD102SN1B ________________________________________________________________ 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 MAX3741 General Description MAX3741 3.2Gbps Compact SFP VCSEL Driver ABSOLUTE MAXIMUM RATINGS Supply Voltage (VCC) ............................................-0.5V to +5.0V Voltage at TX_DISABLE, IN+, IN-, MODSET, PEAKSET, BIASSET, BIAS, BIASMON .......-0.5V to (VCC + 0.5V) Voltage at OUT+, OUT- .........................(VCC - 2V) to (VCC + 2V) Current into OUT+, OUT- ....................................................60mA Continuous Power Dissipation (TA = +85°C) 16-Lead Thin QFN (derate 25mW/°C above +85°C) ..........2W Operating Temperature Range .......................... -40°C to +85°C Storage Temperature Range .............................-55°C to +150°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. ELECTRICAL CHARACTERISTICS (VCC = +2.97V to +3.63V, TA = -40°C to +85°C. Typical values are at VCC = +3.3V, TA = +25°C, unless otherwise noted.) PARAMETER Supply Current SYMBOL ICC ICC-SHDW CONDITIONS TX_DISABLE set low, peaking is not used (Note 1) MIN TYP MAX IMOD = 2mAP-P 41 IMOD = 15mAP-P 51 65 Additional current when peaking is used (Note 2) 14 20 Total current when TX_DISABLE is high 0.15 1 UNITS mA TX_DISABLE INPUT Input Impedance 80 Input High Voltage VIH Input Low Voltage VIL t_off TX_DISABLE Time t_on Input Leakage 105 kΩ 2 V 0.8 Time from rising edge of TX_DISABLE to IBIAS = IBIAS_OFF and IMOD = IMOD_OFF (Note 3) 0.2 Time from falling edge of TX_DISABLE to IBIAS = 15mA and IMOD = 15mAP-P 111 VCC = 0V and VTX_DISABLE = 3.3V 25 V 3 µs 40 µA BIAS GENERATOR (Note 4) Bias Current Accuracy of Programmed Bias Current Bias Current During Disable IBIAS Min Max ∆IBIAS IBIAS_OFF 1 15 -8 +8 TX_DISABLE high BIASMON Gain 0.095 0.115 mA % 10 µA 0.135 mA/mA 2200 mVP-P 80 Ω LASER MODULATOR (Note 5) Data Input Voltage Swing Output Resistance Modulation Current 2 VID ROUT IMOD Total differential signal 250 Single-ended resistance at OUT+, OUT- 63 Min Max 2 15 _______________________________________________________________________________________ mAP-P 3.2Gbps Compact SFP VCSEL Driver MAX3741 ELECTRICAL CHARACTERISTICS (continued) (VCC = +2.97V to +3.63V, TA = -40°C to +85°C. Typical values are at VCC = +3.3V, TA = +25°C, unless otherwise noted.) PARAMETER SYMBOL Programmable Peaking Current IPEAK CONDITIONS MIN TYP Min 0.2 Max 2 Peaking Current Duration MAX mA 80 Tolerance of Programmed Modulation Current ps -10 Modulation Transition Time tR, tF UNITS +10 % ps 5mAP-P ≤ IMOD ≤ 15mAP-P (Note 3) 65 95 Deterministic Jitter DJ 5mAP-P ≤ IMOD ≤ 15mAP-P (Notes 3, 6) 13 25 psP-P Random Jitter RJ (Note 3) 1 4 psRMS 15 50 µAP-P 100 115 Ω Laser Modulation During Disable IMOD_OFF Differential input voltage at 2200mVP-P Differential Input Resistance 85 Input Bias Voltage Note 1: Note 2: Note 3: Note 4: Note 5: Note 6: VCC 0.3 VIN V Measured with RBIASSET = 1.87kΩ (IBIAS ≈ 15mA). Supply current excludes IBIAS. Tested with RPEAK = 1.18kΩ. Guaranteed by design and characterization. VBIAS is less than VCC - 0.7V. Measured electrically with a 50Ω load AC-coupled to OUT+. Deterministic jitter is the peak-to-peak deviation from the ideal time crossings measured with a K28.5 bit pattern at 3.2Gbps (00111110101100000101). Typical Operating Characteristics (VCC = +3.3V, TA = 25°C, measured electrically with a 50Ω load AC-coupled to OUT+, unless otherwise noted.) ELECTRICAL EYE ELECTRICAL EYE WITH PEAKING MAX3741 toc01 3.2Gbps, K28.5, 10mA MODULATION, NO PEAKING 87mV/div MAX3741 toc03 3.2Gbps, K28.5, 10mA MODULATION, RPEAKSET = 2.4kΩ 87mV/div 50ps/div ELECTRICAL EYE WITH PEAKING MAX3741 toc02 3.2Gbps, K28.5, 10mA MODULATION, RPEAKSET = 500Ω 87mV/div 50ps/div 50ps/div _______________________________________________________________________________________ 3 Typical Operating Characteristics (continued) (VCC = +3.3V, TA = 25°C, measured electrically with a 50Ω load AC-coupled to OUT+, unless otherwise noted.) OPTICAL EYE AT 2.125Gbps OPTICAL EYE DETERMINISTIC JITTER vs. IMOD MAX3741 toc05 28 (ER = 8.8dB, 1.063Gbps, K28.5, 850nm VCSEL, WITH 2.3GHz O-TO-E CONVERTER) DETERMINISTIC JITTER (psP-P) (ER = 8.8dB, K28.5, 850nm VCSEL, WITH 2.3GHz O-TO-E CONVERTER) MAX3741 toc06 MAX3741 toc04 24 20 16 12 8 4 0 68ps/div 135ps/div 5 0 10 15 MODULATION CURRENT (mAP-P) BIAS CURRENT vs. RBIASSET 2.0 1.5 12 10 8 6 1.0 4 0.5 2 5 IBIASMON vs. BIAS CURRENT 1.4 5 10 15 20 25 6 4 0 0.8 8 -2 -4 10 12 -6 S22 (dB) S11 (dB) 1.0 6 0 -10 1.2 4 OUTPUT RETURN LOSS DIFFERENTIAL MEASUREMENT -5 2 RMODSET (kΩ) INPUT RETURN LOSS 0.6 -15 -20 -8 -10 -12 -14 -25 0.4 -16 -30 0.2 0 0 4 8 BIAS CURRENT (mA) 4 8 30 0 MAX3741 toc10 1.6 10 RBIASSET (kΩ) MODULATION CURRENT (mAP-P) 1.8 12 0 0 15 10 MAX3741 toc11 0 14 2 0 0 MAX3741 toc09 14 16 MAX3741 toc12 2.5 MAX3741 toc08 MAX3741 toc07 3.0 BIAS CURRENT (mA) RANDOM JITTER (psRMS) 3.5 IMOD vs. RMODSET 16 MODULATION CURRENT (mAP-P) RANDOM JITTER vs. IMOD 4.0 IBIASMON (mA) MAX3741 3.2Gbps Compact SFP VCSEL Driver 12 16 -35 100M -18 1G FREQUENCY (Hz) 10G -20 100M 1G FREQUENCY (Hz) _______________________________________________________________________________________ 10G 3.2Gbps Compact SFP VCSEL Driver RISE TIME 65 60 FALL TIME 55 50 -4 50 40 40 -10 10 2 4 6 8 10 12 14 16 -6 -8 30 20 45 PSR = 20log ∆VOUT ∆VCC -2 60 MAX3741 toc15 POWER-SUPPLY REJECTION 0 PSR (dB) 70 IMOD = 2mAP-P 70 SUPPLY CURRENT (mA) TRANSITION TIME (ps) MAX3741 toc13 MEASURED FROM 20% TO 80% 75 SUPPLY CURRENT vs. TEMPERATURE 80 MAX3741 toc14 TRANSITION TIME vs. IMOD 80 -12 -40 IMOD (mA) -15 10 35 60 85 TEMPERATURE (°C) 100 1k 10k 100k 1M 10M 100M FREQUENCY (Hz) Pin Description PIN NAME FUNCTION 1 TX_DISABLE 2 IN+ Noninverted Data Input 3 IN- Inverted Data Input 4 N.C. No Connection 5, 9, 15 VCC +3.3V Supply Voltage 6 MODSET Modulation Set. A resistor connected from MODSET to ground (RMODSET) programs the desired modulation current amplitude. 7 PEAKSET Peaking Current Set. A resistor connected between PEAKSET and ground (RPEAKSET) programs the peaking current amplitude. To disable peaking, leave PEAKSET open. Transmit Disable. Driver output is disabled when TX_DISABLE is high or left unconnected. The driver output is enabled when the pin is asserted low. 8, 16 GND Ground 10 OUT- Inverted Modulation-Current Output 11 OUT+ Noninverted Modulation-Current Output 12 BIASMON 13 BIAS 14 BIASSET Bias Current Set. A resistor connected between BIASSET and ground (RBIASSET) programs the VCSEL bias current. EP Exposed Pad Ground. This must be soldered to the circuit board ground for proper thermal and electrical performance. See the Layout Considerations section. Bias Current Monitor. The output of BIASMON is a sourced current proportional to the bias current. A resistor connected between BIASMON and ground (RBIASMON) can be used to form a ground referenced bias monitor. Bias Current Output _______________________________________________________________________________________ 5 MAX3741 Typical Operating Characteristics (continued) (VCC = +3.3V, TA = 25°C, measured electrically with a 50Ω load AC-coupled to OUT+, unless otherwise noted.) MAX3741 3.2Gbps Compact SFP VCSEL Driver Functional Diagram BIASSET ENABLE TX_DISABLE BIASMON BIAS GENERATOR VCC BIAS ROUT OUTOUT+ IN+ PEAKING CONTROL 100Ω INENABLE MODULATION-CURRENT GENERATOR MODSET Applications Information VCSEL Selection LASER MODULATOR MAX3741 ROUT Input Termination The MAX3741 data inputs are SFP MSA compatible. On-chip 100Ω differential input impedance is provided for optimal termination (Figure 4). The MAX3741 inputs self-bias to the proper operating point to accommodate AC-coupling. PEAKSET Select a communications-grade VCSEL with a rise time of 260ps or better for 1.25Gbps or 130ps or better for 2.5Gbps applications. Use a high-efficiency VCSEL that requires low modulation current and generates a low voltage swing. Trim the leads to reduce VCSEL package inductance. The typical package leads have inductance of 25nH per inch (1nH/mm). This inductance causes a large voltage swing across the VCSEL. A compensation filter network can be used to reduce ringing, edge speed, and voltage swing. See the Designing the Laser-Compensation Filter Network section for more information. Layout Considerations Detailed Description The MAX3741 contains a bias generator and a laser modulator with optional peaking compensation. To minimize inductance, keep the connections between the MAX3741 output pins and VCSEL as close as possible. Use good high-frequency layout techniques and multiple-layer boards with uninterrupted ground planes to minimize EMI and crosstalk. Bias Generator Figure 1 shows the bias generator circuitry that contains a bandgap voltage reference, current mirror, and bias monitor. The bias current output to the laser is controlled with the RBIASSET resistor. For appropriate RBIASSET values, see the Bias Current vs. RBIASSET graph in the Typical Operating Characteristics. The BIASMON output provides a current proportional to the laser bias current given by: IBIASMON = IBIAS / 9 Modulation Circuit The modulation circuitry consists of an input buffer, a current mirror, and a high-speed current switch (Figure 2). The modulators drive up to 15mA of modulation into a 50Ω VCSEL load. CURRENT AMPLIFIER MAX3741 ENABLE IBIAS 40 BIAS BIASMON IBIAS 9 0.8V 200Ω RBIASMON BIAS GENERATOR BIASSET The amplitude of the modulation current is set with resistor at MODSET (RMODSET). For appropriate RMODSET values, see the IMOD vs. RMODSET graph in the Typical Operating Characteristics. Figure 3 shows a simplified diagram of the MAX3741 output stage. RBIASSET Figure 1. Bias Generator 6 _______________________________________________________________________________________ FERRITE BEAD 3.2Gbps Compact SFP VCSEL Driver MAX3741 ROUT INPUT BUFFER IN+ ROUT OUT+ OUT- CURRENT SWITCH PEAKING CONTROL 100Ω PEAKSET INMODULATION CURRENT GENERATION CURRENT AMPLIFIER 34x RPEAKSET VCSEL package inductance causes the VCSEL impedance to increase at high frequencies, leading to ringing, overshoot, and degradation of the VCSEL output. A VCSEL compensation filter network can be used to reduce the VCSEL impedance at high frequencies, thereby reducing output ringing and overshoot. The compensation components (RF and CF) are most easily determined by experimentation. Begin with RF = 50Ω and CF = 1pF. Increase CF until the desired transmitter response is obtained (Figure 5). Refer to Application Note HFAN-2.0: Interfacing Maxim Laser Drivers with Laser Diodes for more information. ENABLE Exposed-Pad (EP) Package The exposed pad on the 16-pin thin QFN provides a very low thermal resistance path for heat removal from the IC. The pad is electrical ground on the MAX3741 and must be soldered to the circuit board ground for proper thermal and electrical performance. Refer to Maxim Application Note HFAN-08.1: Thermal Considerations for QFN and Other Exposed Pad Packages, for additional information. 1.0V MODSET RMODSET Figure 2. Modulation Circuit VCC MAX3741 ROUT VCC PACKAGE ROUT 1nH 16kΩ OUTPACKAGE VCC 0.5pF IN+ 1nH OUT+ 1nH 0.5pF 50Ω 0.5pF VCC 50Ω IN- 1nH 0.5pF MAX3741 Figure 3. Simplified Output Structure 24kΩ Figure 4. Simplified Input Structure _______________________________________________________________________________________ 7 MAX3741 Designing the Compensation Filter Network VCC Laser Safety and IEC 825 The International Electrotechnical Commission (IEC) determines standards for hazardous light emissions from fiber-optic transmitters. IEC 825 defines the maximum light output for various hazard levels. Using this 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 applications, 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. UNCOMPENSATED CORRECTLY COMPENSATED POWER MAX3741 3.2Gbps Compact SFP VCSEL Driver OVERCOMPENSATED TIME Figure 5. Laser Compensation Chip Information TRANSISTOR COUNT: 1597 PROCESS: SiGe bipolar 8 _______________________________________________________________________________________ 3.2Gbps Compact SFP VCSEL Driver 12x16L QFN THIN.EPS D2 0.10 M C A B b D D2/2 D/2 E/2 E2/2 CL (NE - 1) X e E E2 L e CL k (ND - 1) X e CL 0.10 C CL 0.08 C A A2 A1 L L e e PACKAGE OUTLINE 12, 16L, THIN QFN, 3x3x0.8mm 21-0136 E 1 2 _______________________________________________________________________________________ 9 MAX3741 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.) MAX3741 3.2Gbps Compact SFP VCSEL Driver 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.) EXPOSED PAD VARIATIONS DOWN BONDS ALLOWED NOTES: 1. DIMENSIONING & TOLERANCING CONFORM TO ASME Y14.5M-1994. 2. ALL DIMENSIONS ARE IN MILLIMETERS. ANGLES ARE IN DEGREES. 3. N IS THE TOTAL NUMBER OF TERMINALS. 4. THE TERMINAL #1 IDENTIFIER AND TERMINAL NUMBERING CONVENTION SHALL CONFORM TO JESD 95-1 SPP-012. DETAILS OF TERMINAL #1 IDENTIFIER ARE OPTIONAL, BUT MUST BE LOCATED WITHIN THE ZONE INDICATED. THE TERMINAL #1 IDENTIFIER MAY BE EITHER A MOLD OR MARKED FEATURE. 5. DIMENSION b APPLIES TO METALLIZED TERMINAL AND IS MEASURED BETWEEN 0.20 mm AND 0.25 mm FROM TERMINAL TIP. 6. ND AND NE REFER TO THE NUMBER OF TERMINALS ON EACH D AND E SIDE RESPECTIVELY. 7. DEPOPULATION IS POSSIBLE IN A SYMMETRICAL FASHION. 8. COPLANARITY APPLIES TO THE EXPOSED HEAT SINK SLUG AS WELL AS THE TERMINALS. 9. DRAWING CONFORMS TO JEDEC MO220 REVISION C. PACKAGE OUTLINE 12, 16L, THIN QFN, 3x3x0.8mm 21-0136 E 2 2 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. 10 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.