19-1261; Rev 1; 11/98 L MANUA ION KIT HEET T A U L EVA TA S WS DA FOLLO LED Driver with Programmable Prebias Voltage The MAX3966 can switch up to 100mA into typical high-speed light-emitting diodes. As temperature increases, the device’s modulation current increases with a tempco that is programmable from 2500ppm/°C to 12,000ppm/°C. The modulation current is programmed with a single external resistor. The MAX3966’s LED prebias voltage is programmable from 400mV to 925mV. The prebias circuit produces peaking current, which improves the LED switching speed. Complementary current outputs help to maintain a constant supply current, reducing EMI and supply noise generated by the transmitter module. The MAX3966 is available in die form, or in 16-pin and 24-pin QSOP packages. Features ♦ Programmable LED Prebias Voltage ♦ Single +3V to +5.5V Power Supply ♦ Complementary Output Reduces Supply Noise ♦ Adjustable Modulation Current ♦ Adjustable Temperature Compensation ♦ Available in 16-Pin/24-Pin QSOP or Die Ordering Information PART TEMP. RANGE PIN-PACKAGE MAX3966CEE* 0°C to +70°C 16 QSOP MAX3966CEG MAX3966C/D 0°C to +70°C 0°C to +100°C** 24 QSOP Dice *Some features are not available in the 16-pin QSOP package. Contact factory for information and availability. **Dice are designed to operate over a 0°C to +100°C junction temperature (Tj) range, but are tested and guaranteed only at TA = +25°C. Applications Typical Operating Circuit Multimode LED Transmitters FDDI FERRITE BEAD Fast Ethernet VCC 155Mbps ATMs 0.01µF ESCON VCC 266Mbps Fibre Channel PECL DATA VCCOUT M1 IN+ M2 M3 OUT- LED INVBB MAX3966 OUT+ PB1 PB2 PB3 TCMIN TCNOM TC VEEOUT VEE MOD RMOD NOTE: MODULATION CURRENT IS PROGRAMMED BY RMOD. PREBIAS VOLTAGE IS 0.625V, SET BY PB1, PB2, PB3 PINS. IF DESIRED, MODULATION CAN BE ADJUSTED FROM -4% TO +3% WITH CONNECTIONS TO M1, M2, AND M3. Pin Configurations appear at end of data sheet. ________________________________________________________________ Maxim Integrated Products 1 For free samples and the latest literature, visit www.maxim-ic.com or phone 1-800-998-8800. For small orders, phone 1-800-835-8769. MAX3966 General Description The MAX3966 is a programmable LED driver for fiber optic transmitters operating at data rates up to 266Mbps. The circuit contains a high-speed current driver with programmable temperature coefficient (tempco), adjustments for LED prebias voltage, and a VBB reference voltage generator. The circuit accepts PECL data inputs, and operates from a single +3V to +5.5V power supply. MAX3966 LED Driver with Programmable Prebias Voltage ABSOLUTE MAXIMUM RATINGS Supply Voltage at VCC, VCCOUT (VEE = 0V) ...............-0.5V to 7V Current into OUT+, OUT- ..................................-40mA to 160mA Differential Output Voltage (VOUT+ to VOUT-) .........-3.3V to 3.3V Voltage at M1, M2, M3, PB1, PB2, PB3, IN+, IN-, OUT+, OUT-, VBB ....................-0.5V to (VCC + 0.5V) Voltage at TCMIN, TCNOM, TC, MOD.......................-0.5V to 2V Continuous Power Dissipation (TA = +70°C) 16-pin QSOP (derate 8.3mW/°C above +70°C)......667mW/°C 24-pin QSOP (derate 10mW/°C above +70°C).......770mW/°C Operating Junction Temperature Range ...........-50°C to +150°C Die Attach Temperature...................................................+400°C Storage Temperature Range .............................-50°C to +150°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 (Load as specified in Figure 1; VCC = 3.0V to 5.5V, VEE = 0V, TA = 0°C to +70°C, unless otherwise noted. Temperature coefficients are referenced to TA = +25°C. Typical values are at TA = +25°C, VCC = 3.3V, unless otherwise noted. Dice are tested at TA = +25°C only.) PARAMETER CONDITIONS MIN Data Input High Voltage Referenced to VCC -1.165 Data Input Low Voltage Referenced to VCC -1.810 Supply Current (Note 1) Input Current at IN+ or INMaximum Programmable Modulation Current TYP 30 -50 (Note 2) 100 Prebias Voltage (Note 3) -10 VBB Voltage Prebias Resistor (RPREBIAS) V -1.475 V 35 mA 50 µA mA 40 mA 10 % PB1, PB2, PB3 = (open, open, open) 0.380 0.400 0.428 PB1, PB2, PB3 = (VEE, VEE, open) 0.594 0.625 0.663 PB1, PB2, PB3 = (VEE, VEE, VEE) 0.879 0.925 0.981 Maximum tempco (TC open) Temperature Coefficient of Modulation Current UNITS 130 Minimum Programmable Modulation Current Modulation-Current Accuracy MAX -0.880 12,000 Nominal tempco (TC, TCNOM shorted) 3600 Minimum tempco (TC, TCMIN shorted) 2500 Referenced to VCC V ppm/°C ppm/°C -1.38 -1.33 -1.26 V 66.3 78 89.7 Ω Note 1: RMOD = 1kΩ. Excludes IOUT+ and IOUT-. Note 2: VCC = 3.0V. RMOD = 698Ω, TC connected to TCMIN. Note 3: VCC = 3.3V, VLED = 1.55V, prebias voltage programmed at 0.625V (nominal), TA = +25°C. RMOD = 1kΩ, and programs approximately 80mA current. M1 = VCC, M2 = open, M3 = open, TC connected to TCNOM. 2 _______________________________________________________________________________________ LED Driver with Programmable Prebias Voltage (Load as specified in Figure 1, unless otherwise noted. VCC = 3.0V to 5.5V, RMOD = 1kΩ, TA = 0°C to +70°C. Input data-edge speed = 1ns (typ), VPREBIAS = 0.625V. Typical values are at TA = +25°C, VCC = 3.3V, nominal tempco.) PARAMETER CONDITIONS MIN TYP MAX UNITS 400 615 1000 ps Output Current Edge Speed 20% to 80%, input is a 12.5MHz square wave Output Current Pulse-Width Correction (PWC) Input is a 12.5MHz square wave (Note 4) -210 Output Current Data-Dependent Jitter 266Mbps (Note 5) 150 155Mbps (Note 6) 215 Random Jitter RMS 1.1 ps ps 330 ps Note 4: PWC = (widthCURRENT ON - widthCURRENT OFF) / 2. Note 5: Test pattern is a 2 - 1PRBS transmitted at 266Mbps (3.75ns per bit). Note 6: Test pattern is a 213 - 1PRBS containing 72 consecutive zeros or 72 consecutive ones. VCC VCC + - VLED 1.55V VCC L1 VPREBIAS FERRITE BEAD OSCILLOSCOPE 0.1µF OUT- OUT+ OUT- OUT+ 453Ω OUT50Ω 5Ω MAX3966 MAX3966 MAX3966 0.1µF 453Ω 50Ω SWITCHING DIODE OUT+ DC ELECTRICAL LOAD (EXCEPT PREBIAS VOLTAGE) DC ELECTRICAL LOAD FOR PREBIAS VOLTAGE AC ELECTRICAL LOAD Figure 1. MAX3966 Output Test Loads _______________________________________________________________________________________ 3 MAX3966 AC ELECTRICAL CHARACTERISTICS __________________________________________Typical Operating Characteristics (MAX3966CEG in Maxim evaluation board. VCC = 3.3V, prebias voltage = 0.625V nominal tempco, RMOD = 1kΩ, TA = +25°C, unless otherwise noted.) 24-PIN QSOP MODULATION CURRENT vs. TEMPERATURE SUPPLY CURRENT (mA) 37 36 35 34 33 32 MINIMUM TEMPCO 100 80 NOMINAL TEMPCO 60 MAXIMUM TEMPCO 40 120 100 MAX3966 TOC3 38 120 MAX3966 TOC2 VCC = 5.5V 39 MODULATION CURRENT (mA) MAX3966 TOC1 40 DIE MODULATION CURRENT vs. TEMPERATURE MODULATION CURRENT (mA) SUPPLY CURRENT vs. TEMPERATURE MINIMUM TEMPCO 80 60 MAXIMUM TEMPCO 40 NOMINAL TEMPCO 20 20 31 30 0 0 10 20 30 40 50 60 70 0 20 40 60 70 80 0 100 20 40 60 80 100 120 AMBIENT TEMPERATURE (°C) AMBIENT TEMPERATURE (°C) JUNCTION TEMPERATURE (°C) MODULATION-CURRENT TEMPCO vs. RTC 24-PIN QSOP MODULATION CURRENT vs. RMOD DIE MODULATION CURRENT vs. RMOD NOMINAL TEMPCO MINIMUM TEMPCO 100 NOMINAL TEMPCO MAXIMUM TEMPCO MAXIMUM TEMPCO 10 1000 1 10 500 100 10 MAX3966 TOC6 MAX3966 TOC5 MINIMUM TEMPCO 100 1000 8000 500 1000 8000 RTC (kΩ) RMOD (Ω) RMOD (kΩ) EYE DIAGRAM (ELECTRICAL) 266Mbps EYE DIAGRAM (OPTICAL) 155Mbps EYE DIAGRAM (OPTICAL) 155Mbps MAX3966 TOC7 MAX3966 TOC9 MAX3966 TOC8 RMOD = 720Ω 10mV/div 4 140 200 MODULATION CURRENT (mA) 10,000 200 MODULATION CURRENT (mA) MAX3966 TOC 4 0 MODULATION-CURRENT TEMPCO (ppm/°C) MAX3966 LED Driver with Programmable Prebias Voltage 7mV/div 5mV/div 500ps/div 644ps/div VCC = 3.3V, TA = +25°C, PATTERN = 223 - 1 PRBS 117MHz BESSEL FILTER, VCC = 3.0V, TA = +70°C, PAVE = -18.43dBm, PATTERN = 223 - 1 PRBS 644ps/div 117MHz BESSEL FILTER, VCC = 5.5V, TA = 0°C, PAVE = -16.86dBm, PATTERN = 223 - 1 PRBS _______________________________________________________________________________________ LED Driver with Programmable Prebias Voltage EYE DIAGRAM (OPTICAL) 155Mbps RANDOM JITTER vs. TEMPERATURE MAX3966 TOC11 7mV/div 5mV/div 2.5 RMS RANDOM JITTER (ps) MAX3966 TOC10 VCC = 3.0V MAXIMUM TEMPCO 2.0 1.5 1.0 0.5 VCC = 5.0V MINIMUM TEMPCO 0.0 644ps/div 644ps/div 117MHz BESSEL FILTER, VCC = 5.5V, TA = +70°C, PAVE = -18.19dBm, PATTERN = 223 - 1 PRBS MAX3966 TOC12 EYE DIAGRAM (OPTICAL) 155Mbps 0 117MHz BESSEL FILTER, VCC = 3.0V, TA = 0°C, PAVE = -17.04, PATTERN = 223 - 1 PRBS 10 20 30 40 50 60 70 80 AMBIENT TEMPERATURE (°C) ______________________________________________________________Pin Description PIN NAME NAME FUNCTION 24-PIN 16-PIN 1, 2, 24 — M2, M3, M1 3 2 MOD A resistor from MOD to VEE programs the LED modulation current. 4, 23 1 VCC Provides current to the internal amplifiers. 5 3 VBB Input Reference Voltage PECL Threshold Voltage Output. Connect VBB to IN- for singleended input. 6 4 IN- Inverting Data Input 7 5 IN+ Noninverting Data Input 8 6 VEE Ground for Internal Amplifiers 9 7 TCMIN Shorting TC to TCMIN provides the minimum modulation-current tempco. 10 — TCNOM Shorting TC to TCNOM provides a modulation tempco of approximately 3600ppm/°C. 11 8 TC 12, 13, 14 — PB1, PB2, PB3 15, 16 9, 10 VEEOUT 17, 18 11, 12 OUT+ Current-Output Pins 19, 20 13, 14 OUT- Complementary Current-Output Pins 21, 22 15, 16 VCCOUT Pins M1, M2, and M3 provide fine adjustment of the modulation current (Table 2). A resistor connected between the TC and TCMIN pins sets the tempco of the modulation current. Leaving TC unconnected provides the maximum tempco. Programs the voltage prebias at the OUT+ pin (Table 1). Ground for the Output Current Drivers Supply Connection for the Output Current Drivers _______________________________________________________________________________________ 5 MAX3966 ____________________________Typical Operating Characteristics (continued) (MAX3966CEG in Maxim evaluation board. VCC = 3.3V, prebias voltage = 0.625V nominal tempco, RMOD = 1kΩ, TA = +25°C, unless otherwise noted.) MAX3966 LED Driver with Programmable Prebias Voltage Reference-Voltage Generator and Temperature Compensation _______________Detailed Description The MAX3966 provides a flexible current drive for the modulation of fiber optic light-emitting diodes (LEDs). The circuit is designed to be used with +3.3V or +5V power supplies. The IC provides up to 100mA of modulation current. An adjustable prebias current source sets the LED prebias voltage. An integrated resistor provides passive peaking and optical pulse-width compensation. Figure 2 shows a block diagram of the MAX3966, which comprises a reference-voltage generator, modulationcurrent generator, input buffer, prebias current generator, main output driver, complementary output driver, and LED-compensation network. VCC The reference-voltage generator circuit provides the supply-referenced VBB reference voltage and a reference voltage for the modulation-current generator. A PECL-compatible VBB generator is provided to simplify operation with a single-ended data input. For single-ended operation, connect the input signal to IN+, and connect VBB directly to IN-. The VBB circuit is not designed to drive other external circuitry. The VBB output is implemented with an NPN emitter follower. The reference-voltage generator circuit provides two voltage sources that create modulation-current temperature compensation. A positive modulation-current VEE VCCOUT OUT- VCC INPUT BUFFER IN+ MAX3966 IN- COMPLEMENTARY OUTPUT 24X 5Ω MAIN OUTPUT 24X 78Ω VCC + - VBB MODULATION CURRENT GENERATOR 1.32V OUT+ GAIN 4X 35Ω REFERENCE VOLTAGE GENERATOR 12pF + - 1.2V V + 50Ω TEMP TCMIN TCNOM TC M1 M2 M3 PREBIAS CURRENT GENERATOR MOD RMOD PB1 PB2 PB3 Figure 2. Functional Diagram 6 _______________________________________________________________________________________ LED Driver with Programmable Prebias Voltage Input Buffer The inputs are connected to the PECL-compatible differential input buffer. If left unconnected, IN+ is internally pulled to a PECL low and IN- is pulled to a PECL high, causing low light output. The input impedance of IN+ and IN- is approximately 50kΩ. voltage. The prebias voltage can be adjusted by selectively connecting pins PB1, PB2, and PB3 to V EE . Table 1 describes the functions of PB1, PB2, and PB3. Output Current Drivers The modulation-current reference is switched and amplified by the output stages, which are implemented with NPN current mirrors. LED package lead inductance causes ringing and overshoot, which can be compensated with an RC filter network. The MAX3966 includes 35Ω and 12pF of internal compensation. The compensation network can be optimized by adding additional components between VCCOUT and OUT+. The MAX3966 includes a complementary output driver, which is switched 180° out of phase with the main output. This configuration helps to maintain constant current flow from the voltage supply, reducing noise and EMI. A large diode and a 5Ω resistor are connected in series with the negative output (OUT-) to emulate the LED load at OUT+. Modulation-Current Generator The modulation-current generator circuit provides control of the modulation-current amplitude. This amplitude is determined by the voltage at the MOD pin and external resistor RMOD. Pins M1, M2, and M3 can be selectively connected to the positive supply to provide fine adjustment of the modulation current. Table 2 describes the functions of the M1, M2, and M3 pins. Do not connect bypass capacitors at the MOD pin. Capacitance at this pin increases high-frequency output noise. Peaking Current The prebias resistor provides peaking current to improve the LED switching speed. The peaking magnitude is given by the following equation: PEAKINGCURRENT ≅ VLED − VPREBIAS 78Ω The peaking amplitude is equal for rising and falling data transitions. Prebias Current Generator __________________Design Procedure A prebias voltage (VPREBIAS) can be applied to the LED to improve switching speed. The prebias current generator creates a current that flows through the 78Ω prebias resistor in the output stage, creating a prebias For best performance, select a high-efficiency, lowinductance LED. LED inductance causes large voltage swings and ringing. Table 1. LED Prebias Voltage Table 2. Modulation-Current Adjustment PB1 PB2 PB3 PREBIAS (V) Open Open Open 0.400 Select an LED M1 M2 M3 ADJUSTMENT (%) VEE Open Open 0.475 Open Open Open -4.0 Open VEE Open 0.550 Open Open VCC -3.0 VEE VEE Open 0.625 Open VCC Open -2.0 Open Open VEE 0.700 Open VCC VCC -1.0 VEE Open VEE 0.775 VCC Open Open 0 Open VEE VEE 0.850 VCC Open VCC 1.0 VEE VEE VEE 0.925 VCC VCC Open 2.0 VCC VCC VCC 3.0 _______________________________________________________________________________________ 7 MAX3966 temperature coefficient (tempco) is useful to compensate for the temperature characteristics of typical fiber optic LEDs. The first source has a temperaturestable output. The second source has a temperatureincreasing output with a tempco of approximately 12,000ppm/°C (relative to +25°C). A resistor divider between the two reference generators programs the modulation-current tempco. For maximum modulationcurrent tempco, leave the TC pin disconnected. For a tempco of approximately 3600ppm/°C, connect TC to TCNOM. To obtain the minimum tempco, connect TCMIN to TC. Intermediate tempco values can be programmed by connecting an external resistor (R TC ) between TCMIN and TC. MAX3966 LED Driver with Programmable Prebias Voltage Program the Modulation-Current Tempco Select a modulation-current tempco that provides nearly constant LED output power as temperature varies. For the minimum tempco, connect TCMIN to the TC pin. For a tempco of approximately 3600ppm/°C, connect TC to TCNOM and leave TCMIN unconnected. For the maximum tempco, leave TCMIN, TCNOM, and TC unconnected. Refer to the Modulation-Current Temperature Coefficient vs. RTC Resistor graph in the Typical Operating Characteristics to program a custom tempco. From the graph, determine the appropriate resistor and connect it between TCMIN and TC. For example, if an LED requires a 5000 ppm/°C tempco, choose RTC of 10Ω. Applications Information Input Terminations MAX3966 PECL OUTPUT IN+ 50Ω VCC - 2V R1 Program Prebias Voltage Determine the LED prebias voltage that produces an acceptable trade-off between peaking current and extinction ratio. Refer to Table 1 for PB1, PB2, and PB3 settings. MAX3966 RF OR NON-PECL OUTPUT Program the Modulation Current Determine the required modulation current at TA = +25°C. Then select the appropriate value of RMOD from the Modulation Current vs. RMOD graph in the Typical Operating Characteristics, which provides the required current. For example, to program 80mA modulation current, the graph indicates an RMOD value of 750Ω for maximum tempco (12,000ppm/°C) and 1.1kΩ for nominal tempco (3600ppm/°C). By interpolation, choose an RMOD of 1.05kΩ for a tempco of 5000ppm/°C. VCC IN+ R2 VCC R1 R2 3.3 83 126 5.0 68 180 SINGLE-ENDED TERMINATION IS SHOWN. IN- SHOULD BE TERMINATED SIMILARLY OR CONNECTED TO VBB. Figure 3. Input Terminations Wire-Bonding Die The MAX3966 utilizes gold metalization, which provides high reliability. Make connections to the die with gold wire only, using ball-bonding techniques. Wedge bonding is not recommended. Pad size is 4mil square (100µm). Die thickness is typically 15mil (375µm). Layout Considerations For optimum performance, total load inductance should not exceed 10nH. Load inductance includes LED inductance, LED package lead inductance, and circuitboard traces. Keep the connections between the MAX3966 OUT pins and the LED as short as possible to minimize inductance. Chip-and-wire (hybrid) technology reduces package inductance significantly, and provides the best possible performance. Use good high-frequency layout techniques. Use a multilayer board with an uninterrupted ground plane. Power supplies should be capacitively bypassed to the ground plane with surface-mount capacitors located near the power-supply pins. 8 _______________________________________________________________________________________ LED Driver with Programmable Prebias Voltage TOP VIEW M2 1 24 M1 M3 2 23 VCC MOD 3 22 VCCOUT VCC 4 21 VCCOUT VBB 5 MAX3966CEG 20 OUT- IN- 6 19 OUT- IN+ 7 18 OUT+ VEE 8 17 OUT+ TCMIN 9 16 VEEOUT TCNOM 10 15 VEEOUT TC 11 14 PB3 PB1 12 13 PB2 VCC 1 16 VCCOUT MOD 2 15 VCCOUT VBB 3 IN- 4 14 OUT- MAX3966CEE 13 OUT- IN+ 5 12 OUT+ VEE 6 11 OUT+ TCMIN 7 10 VEEOUT TC 8 9 VEEOUT QSOP QSOP _______________________________________________________________________________________ 9 MAX3966 Pin Configurations MAX3966 LED Driver with Programmable Prebias Voltage ___________________Chip Topography TCMIN VEE IN+ IN- VBB TCNOM VCC MOD TC M3 PB1 M2 PB2 M1 PB3 VCC 1.829" (1.829mm) VCCEE VCCOUT VCCEE VCCOUT OUT+ OUT+ OUT- OUT1.168" (1.169mm) TRANSISTOR COUNT: 304 SUBSTRATE CONNECTED TO VEE 10 ______________________________________________________________________________________ LED Driver with Programmable Prebias Voltage QSOP.EPS ______________________________________________________________________________________ 11 MAX3966 ________________________________________________________Package Information LED Driver with Programmable Prebias Voltage MAX3966 NOTES 12 ______________________________________________________________________________________