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19-1261; Rev 1; 11/98
ANUAL N KIT M LUATIO ATA SHEET EVA WS D FOLLO
LED Driver with Programmable Prebias Voltage
Features
o Programmable LED Prebias Voltage o Single +3V to +5.5V Power Supply o Complementary Output Reduces Supply Noise o Adjustable Modulation Current o Adjustable Temperature Compensation o Available in 16-Pin/24-Pin QSOP or Die
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. 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.
MAX3966
Ordering Information
PART MAX3966CEE* MAX3966CEG MAX3966C/D TEMP. RANGE 0C to +70C 0C to +70C 0C to +100C** PIN-PACKAGE 16 QSOP 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 0C to +100C junction temperature (Tj) range, but are tested and guaranteed only at TA = +25C.
Applications
Multimode LED Transmitters FDDI Fast Ethernet 155Mbps ATMs ESCON 266Mbps Fibre Channel
PECL DATA
Typical Operating Circuit
FERRITE BEAD VCC 0.01F VCC IN+ INVBB PB1 PB2 PB3 TCMIN TCNOM TC 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. VEEOUT VEE VCCOUT M1 M2 M3 OUTLED
MAX3966
OUT+
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.
LED Driver with Programmable Prebias Voltage MAX3966
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 = +70C) 16-pin QSOP (derate 8.3mW/C above +70C)......667mW/C 24-pin QSOP (derate 10mW/C above +70C).......770mW/C Operating Junction Temperature Range ...........-50C to +150C Die Attach Temperature...................................................+400C Storage Temperature Range .............................-50C to +150C Lead Temperature (soldering, 10sec) .............................+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
(Load as specified in Figure 1; VCC = 3.0V to 5.5V, VEE = 0V, TA = 0C to +70C, unless otherwise noted. Temperature coefficients are referenced to TA = +25C. Typical values are at TA = +25C, VCC = 3.3V, unless otherwise noted. Dice are tested at TA = +25C only.) PARAMETER Data Input High Voltage Data Input Low Voltage Supply Current Input Current at IN+ or INMaximum Programmable Modulation Current Minimum Programmable Modulation Current Modulation-Current Accuracy Prebias Voltage (Note 3) PB1, PB2, PB3 = (open, open, open) PB1, PB2, PB3 = (VEE, VEE, open) PB1, PB2, PB3 = (VEE, VEE, VEE) Maximum tempco (TC open) Temperature Coefficient of Modulation Current VBB Voltage Prebias Resistor (RPREBIAS) Nominal tempco (TC, TCNOM shorted) Minimum tempco (TC, TCMIN shorted) Referenced to VCC -1.38 66.3 -10 0.380 0.594 0.879 0.400 0.625 0.925 12,000 3600 2500 -1.33 78 -1.26 89.7 ppm/C ppm/C V (Note 2) Referenced to VCC Referenced to VCC (Note 1) -50 100 130 40 10 0.428 0.663 0.981 V CONDITIONS MIN -1.165 -1.810 30 TYP MAX -0.880 -1.475 35 50 UNITS V V mA A mA mA %
Note 1: RMOD = 1k. Excludes IOUT+ and IOUT-. Note 2: VCC = 3.0V. RMOD = 698, TC connected to TCMIN. Note 3: VCC = 3.3V, VLED = 1.55V, prebias voltage programmed at 0.625V (nominal), TA = +25C. RMOD = 1k, and programs approximately 80mA current. M1 = VCC, M2 = open, M3 = open, TC connected to TCNOM.
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LED Driver with Programmable Prebias Voltage
AC ELECTRICAL CHARACTERISTICS
(Load as specified in Figure 1, unless otherwise noted. VCC = 3.0V to 5.5V, RMOD = 1k, TA = 0C to +70C. Input data-edge speed = 1ns (typ), VPREBIAS = 0.625V. Typical values are at TA = +25C, VCC = 3.3V, nominal tempco.) PARAMETER Output Current Edge Speed Output Current Pulse-Width Correction (PWC) Output Current Data-Dependent Jitter Random Jitter CONDITIONS 20% to 80%, input is a 12.5MHz square wave Input is a 12.5MHz square wave (Note 4) 266Mbps (Note 5) 155Mbps (Note 6) RMS MIN 400 TYP 615 -210 150 215 1.1 330 MAX 1000 UNITS ps ps ps ps
MAX3966
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
+ OUTOUT+
VLED 1.55V
VCC
VPREBIAS OUTOUT+ OUT-
L1
FERRITE BEAD 0.1F 453
OSCILLOSCOPE
50 5
MAX3966
MAX3966
MAX3966
0.1F 453
50
SWITCHING DIODE OUT+
DC ELECTRICAL LOAD (EXCEPT PREBIAS VOLTAGE) Figure 1. MAX3966 Output Test Loads
DC ELECTRICAL LOAD FOR PREBIAS VOLTAGE
AC ELECTRICAL LOAD
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LED Driver with Programmable Prebias Voltage MAX3966
__________________________________________Typical Operating Characteristics
(MAX3966CEG in Maxim evaluation board. VCC = 3.3V, prebias voltage = 0.625V nominal tempco, RMOD = 1k, TA = +25C, unless otherwise noted.)
SUPPLY CURRENT vs. TEMPERATURE
MAX3966 TOC1
24-PIN QSOP MODULATION CURRENT vs. TEMPERATURE
DIE MODULATION CURRENT vs. TEMPERATURE
MAX3966 TOC2 MAX3966 TOC3
40 39 38 SUPPLY CURRENT (mA) 37 36 35 34 33 32 31 30 0 10 20 30 40 50 60 VCC = 5.5V
120 MINIMUM TEMPCO MODULATION CURRENT (mA) 100 80 60 40 20 0 NOMINAL TEMPCO MAXIMUM TEMPCO
120 100 80 60 40 20 0
MODULATION CURRENT (mA)
MINIMUM TEMPCO
MAXIMUM TEMPCO NOMINAL TEMPCO
70
0
20
40
60
70
80
100
0
20
40
60
80
100
120
140
AMBIENT TEMPERATURE (C)
AMBIENT TEMPERATURE (C)
JUNCTION TEMPERATURE (C)
MODULATION-CURRENT TEMPCO vs. RTC
MODULATION-CURRENT TEMPCO (ppm/C)
MAX3966 TOC 4
24-PIN QSOP MODULATION CURRENT vs. RMOD
MAX3966 TOC5
DIE MODULATION CURRENT vs. RMOD
MAX3966 TOC6
200 MINIMUM TEMPCO 100
200 MINIMUM TEMPCO 100
MODULATION CURRENT (mA)
10,000
MODULATION CURRENT (mA)
NOMINAL TEMPCO MAXIMUM TEMPCO
NOMINAL TEMPCO MAXIMUM TEMPCO 10
1000 1 10 RTC (k) 100
10 500 1000 RMOD () 8000
500
1000 RMOD (k)
8000
EYE DIAGRAM (ELECTRICAL) 266Mbps
MAX3966 TOC7
EYE DIAGRAM (OPTICAL) 155Mbps
MAX3966 TOC8
EYE DIAGRAM (OPTICAL) 155Mbps
MAX3966 TOC9
RMOD = 720
10mV/div
5mV/div
7mV/div
500ps/div VCC = 3.3V, TA = +25C, PATTERN = 223 - 1 PRBS
644ps/div 117MHz BESSEL FILTER, VCC = 3.0V, TA = +70C, PAVE = -18.43dBm, PATTERN = 223 - 1 PRBS
644ps/div 117MHz BESSEL FILTER, VCC = 5.5V, TA = 0C, PAVE = -16.86dBm, PATTERN = 223 - 1 PRBS
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LED Driver with Programmable Prebias Voltage
____________________________Typical Operating Characteristics (continued)
(MAX3966CEG in Maxim evaluation board. VCC = 3.3V, prebias voltage = 0.625V nominal tempco, RMOD = 1k, TA = +25C, unless otherwise noted.)
EYE DIAGRAM (OPTICAL) 155Mbps
MAX3966 TOC10
MAX3966
EYE DIAGRAM (OPTICAL) 155Mbps
MAX3966 TOC11
RANDOM JITTER vs. TEMPERATURE
MAX3966 TOC12
2.5 VCC = 3.0V MAXIMUM TEMPCO
5mV/div
7mV/div
RMS RANDOM JITTER (ps)
2.0
1.5
1.0
0.5
0.0 644ps/div 117MHz BESSEL FILTER, VCC = 5.5V, TA = +70C, PAVE = -18.19dBm, PATTERN = 223 - 1 PRBS 644ps/div 117MHz BESSEL FILTER, VCC = 3.0V, TA = 0C, PAVE = -17.04, PATTERN = 223 - 1 PRBS 0 10
VCC = 5.0V MINIMUM TEMPCO 20 30 40 50 60 70 80
AMBIENT TEMPERATURE (C)
______________________________________________________________Pin Description
PIN NAME NAME 24-PIN 1, 2, 24 3 4, 23 5 6 7 8 9 10 11 12, 13, 14 15, 16 17, 18 19, 20 21, 22 16-PIN -- 2 1 3 4 5 6 7 -- 8 -- 9, 10 11, 12 13, 14 15, 16 M2, M3, M1 MOD VCC VBB ININ+ VEE TCMIN TCNOM TC PB1, PB2, PB3 VEEOUT OUT+ OUTVCCOUT Pins M1, M2, and M3 provide fine adjustment of the modulation current (Table 2). A resistor from MOD to VEE programs the LED modulation current. Provides current to the internal amplifiers. Input Reference Voltage PECL Threshold Voltage Output. Connect VBB to IN- for singleended input. Inverting Data Input Noninverting Data Input Ground for Internal Amplifiers Shorting TC to TCMIN provides the minimum modulation-current tempco. Shorting TC to TCNOM provides a modulation tempco of approximately 3600ppm/C. 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 Current-Output Pins Complementary Current-Output Pins Supply Connection for the Output Current Drivers 5 FUNCTION
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LED Driver with Programmable Prebias Voltage MAX3966
_______________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.
Reference-Voltage Generator and Temperature Compensation
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
VCC
VEE
VCCOUT OUT-
VCC IN+ ININPUT BUFFER
MAX3966
COMPLEMENTARY OUTPUT 24X 5
VCC
VBB
+ -
1.32V
MODULATION CURRENT GENERATOR
MAIN OUTPUT 24X GAIN 4X
78
OUT+ 35
REFERENCE VOLTAGE GENERATOR 12pF
+ -
1.2V
V
+ TEMP 50
PREBIAS CURRENT GENERATOR
TCMIN
TCNOM
TC
M1
M2
M3
MOD RMOD
PB1
PB2
PB3
Figure 2. Functional Diagram 6 _______________________________________________________________________________________
LED Driver with Programmable Prebias Voltage
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 +25C). 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. 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.
MAX3966
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 35 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 5 resistor are connected in series with the negative output (OUT-) to emulate the LED load at OUT+.
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 50k.
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 78
The peaking amplitude is equal for rising and falling data transitions.
Prebias Current Generator
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 78 prebias resistor in the output stage, creating a prebias
__________________Design Procedure
Select an LED
For best performance, select a high-efficiency, lowinductance LED. LED inductance causes large voltage swings and ringing.
Table 1. LED Prebias Voltage
PB1 Open VEE Open VEE Open VEE Open VEE PB2 Open Open VEE VEE Open Open VEE VEE PB3 Open Open Open Open VEE VEE VEE VEE PREBIAS (V) 0.400 0.475 0.550 0.625 0.700 0.775 0.850 0.925
Table 2. Modulation-Current Adjustment
M1 Open Open Open Open VCC VCC VCC VCC M2 Open Open VCC VCC Open Open VCC VCC M3 Open VCC Open VCC Open VCC Open VCC ADJUSTMENT (%) -4.0 -3.0 -2.0 -1.0 0 1.0 2.0 3.0 7
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LED Driver with Programmable Prebias Voltage MAX3966
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 10.
Applications Information
Input Terminations
PECL OUTPUT 50 VCC - 2V
MAX3966 IN+
VCC R1
RF OR NON-PECL OUTPUT R2 VCC 3.3 5.0 R1 83 68 R2 126 180
MAX3966 IN+
Program the Modulation Current
Determine the required modulation current at TA = +25C. 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 750 for maximum tempco (12,000ppm/C) and 1.1k for nominal tempco (3600ppm/C). By interpolation, choose an RMOD of 1.05k for a tempco of 5000ppm/C.
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 (100m). Die thickness is typically 15mil (375m).
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.
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.
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LED Driver with Programmable Prebias Voltage
Pin Configurations
TOP VIEW
M2 1 M3 2 MOD 3 VCC 4 VBB 5 IN- 6 IN+ 7 VEE 8 TCMIN 9 TCNOM 10 TC 11 PB1 12 24 M1 23 VCC 22 VCCOUT 21 VCCOUT VCC 1 MOD 2 VBB 3 IN- 4 IN+ 5 VEE 6 16 VEEOUT 15 VEEOUT 14 PB3 13 PB2 TCMIN 7 TC 8 16 VCCOUT 15 VCCOUT 14 OUT-
MAX3966
MAX3966CEG
20 OUT19 OUT18 OUT+ 17 OUT+
MAX3966CEE
13 OUT12 OUT+ 11 OUT+ 10 VEEOUT 9 VEEOUT
QSOP
QSOP
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LED Driver with Programmable Prebias Voltage MAX3966
___________________Chip Topography
TCMIN VEE IN+ INVBB VCC
TCNOM
MOD
TC PB1 PB2 PB3
M3
M2 M1 VCC
1.829" (1.829mm) VCCEE VCCEE VCCOUT VCCOUT
OUT+ OUT+ OUT- OUT1.168" (1.169mm)
TRANSISTOR COUNT: 304 SUBSTRATE CONNECTED TO VEE
10
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LED Driver with Programmable Prebias Voltage
________________________________________________________Package Information
QSOP.EPS
MAX3966
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11
LED Driver with Programmable Prebias Voltage MAX3966
NOTES
12
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