MAX3643ETG+

EVALUATION KIT AVAILABLE
MAX3643
155Mbps to 2.5Gbps Burst-Mode Laser Driver
General Description
Features
The MAX3643 burst-mode laser driver provides bias and
modulation current drive for PON burst-mode ONT applications. It is specifically designed for use with a low-cost
external controller for the APC (and if desired, AMC) loop.
A high-speed differential burst-enable input enables the
driver to switch the laser from a dark (output off) condition
to full on-condition in less than 2ns. When BEN is inactive, typical modulation and bias currents are 5µA each.
Laser modulation current can be set from 10mA to
85mA and bias current can be set from 1mA to 70mA
using the MODSET and BIASSET inputs. A sample-andhold circuit is provided to capture the monitor diode
output during short PON bursts, if needed, and the BEN
high-speed signal is mirrored on an LVCMOS output to
be used by the controller operating the APC/AMC loop.
♦ 10mA to 85mA Modulation Current
♦ 1mA to 70mA Bias Current
♦ Monitor Diode Sample and Hold
♦ 45ps Output Transition Time
♦ 2ns Turn-On/-Off Time
♦ Reference Voltage Generator
♦ LVPECL High-Speed Inputs (Data, Burst Enable)
Ordering Information
PART
The MAX3643 burst-mode laser driver is packaged in a
4mm x 4mm, 24-pin thin QFN package. It operates from
-40°C to +85°C.
TEMP RANGE
PIN-PACKAGE
MAX3643ETG
-40°C to +85°C
24 TQFN-EP*
MAX3643ETG+
-40°C to +85°C
24 TQFN-EP*
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed paddle.
Applications
A/B/G/XGPON ONT Modules Up to 2.5Gbps
Pin Configuration appears at end of data sheet.
1.25Gbps IEEE EPON ONT Modules
Typical Application Circuit
3.3V
15Ω
3.3V
+3.3V
130Ω
FILTER
130Ω
VCC
SERIAL
DATA
SOURCE
10nH
Z0 = 50Ω
IN+
Z0 = 50Ω
IN-
15Ω
OUT5.6Ω
OUT+
82Ω
82Ω
10pF
5.6Ω
75Ω
1kΩ
BIAS+
MAX3643
27pF
3.3V
+3.3V
10Ω
BIAS-
82Ω
BCMON
BENOUT
BIASSET
VBSET
VREF
BEN-
MODSET
Z0 = 50Ω
VMSET
BEN+
IMAX
MDIN
Z0 = 50Ω
EN
BURST
CONTROL
130Ω
GND
130Ω
MDOUT
82Ω
BMD
MON1
3kΩ
1kΩ
1kΩ
DS1875
PON TRIPLEXER AND SFP
CONTROLLER
BEN
BIAS
MOD
For pricing, delivery, and ordering information, please contact Maxim Direct at
1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.
19-3848; Rev 4; 12/12
MAX3643
155Mbps to 2.5Gbps Burst-Mode Laser Driver
ABSOLUTE MAXIMUM RATINGS
Supply Voltage VCC ..............................................-0.5V to +4.0V
Current into BIAS-, BIAS+, OUT-, OUT+ .......-20mA to +150mA
Voltage at VMSET, VBSET, IN+, IN-, BEN+, BEN-, EN, MDIN,
MDOUT, BENOUT, BCMON ...................-0.5V to (VCC + 0.5V)
Voltage at MODSET, BIASSET, VREF, IMAX ........-0.5V to +3.0V
Voltage at OUT-, OUT+, BIAS-, BIAS+ .....+0.3V to (VCC + 0.5V)
Continuous Power Dissipation (TA = +85°C)
24-Pin TQFN, Multilayer Board
(derate 27.8mW/°C above +85°C) ............................1807mW
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range ............................-55°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Soldering Temperature (reflow)
Lead(Pb)-free..............................................................+260°C
Containing lead(Pb) ....................................................+240°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.
OPERATING CONDITIONS
PARAMETER
SYMBOL
Supply Turn-On Time
CONDITIONS
10% to 90%
MIN
TYP
0.001
Ambient Temperature
-40
Data Rate
Voltage at VMSET, VBSET
0
MAX
UNITS
1000
ms
+85
°C
2500
Mbps
1.4
V
Voltage at BCMON
0
1.4
V
Voltage at MDIN
0
2.56
V
ELECTRICAL CHARACTERISTICS
(VCC = 3.0V to 3.6V, TA = -40°C to +85°C. Typical values are at VCC = 3.3V, TA = +25°C, IBIAS = 20mA, IMOD = 30mA, unless otherwise noted.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
Supply Current
ICC
Excluding laser bias and mode currents,
max at IMOD = 85mA, IBIAS = 70mA
I/O SPECIFICATIONS
LVPECL Differential Input
VIN
VIN = (VIN+) - (VIN-)
LVPECL Common-Mode Input
Voltage
I OH = -100μA
LVCMOS Output Low Voltage
I OL = 100μA
BENOUT Propagation Delay
CL = 20pF, from BEN zero crossing to 67%
CMOS level
Td
LVCMOS Input Pullup
TYP
MAX
UNITS
32
51
mA
1600
mVP-P
VCC VIN / 4
V
200
VCC 1.49
VCM
LVCMOS Output High Voltage
MIN
VCC 1.32
VCC 0.2
V
0.2
30
ns
75
LVCMOS Input Current
V
k
50
μA
LVCMOS Input High Voltage
VIN = 0V or VIN = VCC
2.0
VCC
V
LVCMOS Input Low Voltage
0.2
0.8
V
70
mA
50
μA
mA/mA
BIAS GENERATOR SPECIFICATIONS
Bias Current Range
IBIAS
Bias Current, Burst Off
IBIAS, OFF
BIASSET Current Gain
GBIAS
VBIAS+, VBIAS- 0.6V
1
BEN = low or EN = high
5
1mA IBIAS < 2mA, VBSET = VREF
2
88
2mA IBIAS < 10mA, VBSET = VREF
70
88
110
10mA IBIAS < 70mA, VBSET = VREF
82.5
88
94.5
Maxim Integrated
MAX3643
155Mbps to 2.5Gbps Burst-Mode Laser Driver
ELECTRICAL CHARACTERISTICS (continued)
(VCC = 3.0V to 3.6V, TA = -40°C to +85°C. Typical values are at VCC = 3.3V, TA = +25°C, IBIAS = 20mA, IMOD = 30mA, unless otherwise noted.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
BIASSET Current Gain Stability
5mA IBIAS 70mA (Note 13)
-4.4
+4.4
%
BIASSET Current Gain Linearity
5mA IBIAS 70mA (Note 14)
-3.75
+3.75
%
Bias Current Overshoot
VCC turn-on/-off < 1s
10
%
17
mA/A
Bias Current Monitor Gain
GBSM
Bias Current Monitor Gain
Stability
BIASSET Resistor
2mA IBIAS 70mA, VBSET = VREF
11
1mA IBIAS < 5mA
5mA IBIAS 70mA
14
±4
-5
RBIAS
40
IMOD
10
%
+5
50
60
85
mA
120
μA
MODULATOR SPECIFICATIONS
Modulation Current Range
Modulation Current Off
IMOD, OFF
Instantaneous Voltage at OUT+
MODSET Current Gain
GMOD
BEN = low or EN = high or VIN = low
5
10mA IMOD < 60mA
0.6
60mA IMOD 85mA
0.75
V
10mA < IMOD < 85mA, VMSET = VREF
82.5
94.5
mA/mA
MODSET Current Gain Stability
(Note 13)
-4.4
+4.4
%
MODSET Current Gain Linearity
(Note 14)
-2.2
+2.2
%
IBIASSET = 0.15mA, IMODSET = 0.7mA
MODSET, BIASSET Gain
Matching (Note 15)
88
0.5
IMODSET = IBIASSET = 0.15mA
1.7
IMODSET = IBIASSET = 0.4mA
IMODSET = IBIASSET = 0.55mA
1
%
1
Modulation Current Rise Time
tR
20% to 80%
45
85
ps
Modulation Current Fall Time
tF
20% to 80%
45
85
ps
Deterministic Jitter
(Note 3)
17
45
psP-P
Random Jitter
(Note 4)
0.8
1.4
psRMS
50
60
1.4
V
±5
mV
1.5
μA
MODSET Resistor
RMOD
40
MODSET, BIASSET OPERATIONAL AMPLIFIER SPECIFICATIONS
MODSET, BIASSET Voltage
Range
0.005
Voltage Error
(Note 5)
Input Leakage
VMSET and VBSET pins
0.1
TURN-OFF/-ON SPECIFICATIONS
Burst-Enable Time
(Notes 2, 6, 7)
2.3
ns
Burst-Disable Time
(Notes 2, 6, 8)
2.0
ns
2.56
V
±1
mV
SAMPLE/HOLD SPECIFICATIONS
MDIN Voltage Range
MDOUT Settling
Sample/Hold Droop
Bias Current Overshoot
Maxim Integrated
0.05
Relative to final value at 3μs, CL < 20pF
±2.56
mV
VCC turn-on/-off < 1s, IBIAS 20mA
After 100μs (Note 9)
10
%
IBIAS < 20mA
2
mA
3
MAX3643
155Mbps to 2.5Gbps Burst-Mode Laser Driver
ELECTRICAL CHARACTERISTICS (continued)
(VCC = 3.0V to 3.6V, TA = -40°C to +85°C. Typical values are at VCC = 3.3V, TA = +25°C, IBIAS = 20mA, IMOD = 30mA, unless otherwise noted.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
Final value measured after 10μs
(MDOUT - MDIN), burst width > 576ns
Sampling Error
TYP
MAX
UNITS
3
±14
mV
1.235
1.295
V
BANDGAP VOLTAGE REFERENCE SPECIFICATIONS
VREF Output
RL > 10k, CL < 50pF
1.175
MODULATION/BIAS CURRENT DISABLE
Enable Time
5mA < IBIAS, 10mA < IMOD (Note 10)
5.5
μs
Disable Time
(Notes 2, 11)
375
ns
15
k
100
150
mA
50
75
RIMAX Range
Current Limit (Tested with IBIAS
= IMOD)
3
RIMAX = 3k
IBIAS+I MOD RIMAX = 5k
RIMAX = 10k
155
OPTICAL EVALUATION
Eye Margin (Note 12)
155.52Mbps
49
622.08Mbps
45
1.24416Gbps
38
2.48832Gbps
18
%
Note 1: Electrical specifications are production tested at TA = +25°C. Specifications over the entire operating temperature range
are guaranteed by design and characterization. Typical specifications are at TA = +25°C, 3.3V.
Note 2: For 10mA ≤ IMOD ≤ 85mA and 4mA ≤ IBIAS ≤ 70mA.
Note 3: Deterministic jitter measured with a continuous pattern of 27-1 PRBS, 80 ones, 27-1 PRBS, 80 zeros at 1.25Gbps, and both
LVPECL inputs terminated by the network shown in Figure 3.
Note 4: Random jitter, rise time, fall time measured with 0000011111 pattern at 1.25Gbps.
Note 5: Voltage difference between VMSET and MODSET or VBSET and BIASSET excluding IR drops. The maximum operating
voltage at VMSET or VBSET must be less than 1.4V for proper operation.
Note 6: Turn-on/-off time is when the BEN+/BEN- LVPECL inputs are used to control modulation and bias currents.
Note 7: Burst-enable delay is measured between the time at which the rising edge of the differential burst-enable input reaches the
midpoint, and the time at which the combined output currents (bias plus modulation) reach 90% of their final level.
Note 8: Burst-disable delay is measured between the time at which the falling edge of the differential burst-enable input reaches the
midpoint, and the time at which the combined output currents (bias plus modulation) fall below 10% of the bias-on current.
Note 9: Droop measured with sample/hold output load of 10MΩ.
Note 10: Enable delay is measured between the time at which the falling edge of the EN input reaches ≤ 0.8V, and the time at which
the combined output currents (bias plus modulation) reach 90% of their final level.
Note 11: Disable delay is measured between the time at which the rising edge of the EN input reaches ≥ 2V, and the time at which
the combined output currents (bias plus modulation) fall below 10% of the bias-on current.
Note 12: Excelight SLT2886-LR laser.
Note 13: Current gain stability = [(Gain – nominal Gain) / nominal Gain], nominal Gain at VCC = 3.3V, TA = +25°C.
Note 14: Gain linearity = (Gainmax – Gainmin), Gainavg = Gainmax + Gainmin
Gainavg
2
Note 15: Gain matching = Gain mod / Gainbias − Gain mod nom / Gainbiasnom , nominal at VCC = 3.3V, TA = +25°C.
Gain mod nom / Gainbiasnom
4
Maxim Integrated
MAX3643
155Mbps to 2.5Gbps Burst-Mode Laser Driver
Typical Operating Characteristics
(Typical values are at VCC = 3.3V, TA = +25°C, data pattern = 27-1 PRBS + 80 ones + 27-1 PRBS + 80 zeros, unless otherwise
noted.)
MAX3643 toc01
EXCELIGHT SLT2886-LR LASER
AVERAGE OPTICAL POWER = -6dBm
EXTINCTION RATIO = 15dB
MASK MARGIN = 49%
OPTICAL EYE DIAGRAM
(1.24416Gbps, 933MHz FILTER,
PATTERN = 223 - 1 PRBS)
OPTICAL EYE DIAGRAM
(622.08Mbps, 467MHz FILTER,
PATTERN = 223 - 1 PRBS)
MAX3643 toc03
MAX3643 toc02
EXCELIGHT SLT2886-LR LASER
AVERAGE OPTICAL POWER = -6dBm
EXTINCTION RATIO = 14dB
MASK MARGIN = 38%
EXCELIGHT SLT2886-LR LASER
AVERAGE OPTICAL POWER = -6dBm
EXTINCTION RATIO = 15dB
MASK MARGIN = 45%
OPTICAL EYE DIAGRAM
(2.48832Gbps, 2.3GHz FILTER,
PATTERN = 223 - 1 PRBS)
ELECTRICAL EYE DIAGRAM
(2.5Gbps, IMOD = 30mA,
PATTERN = PRBS 27 - 1 + 80 CID)
SUPPLY CURRENT vs. TEMPERATURE
(IBIAS = 20mA, IMOD = 30mA)
MAX3643 toc05
MAX3643 toc04
60
MAX3643 toc06
OPTICAL EYE DIAGRAM
(155.52Mbps, 117MHz FILTER,
PATTERN = 223 - 1 PRBS)
EXCLUDES BIAS AND
MODULATION CURRENT
55
50
ICC (mA)
45
40
35
30
25
20
15
10
EXCELIGHT SLT2886-LR LASER
AVERAGE OPTICAL POWER = -6dBm
EXTINCTION RATIO = 10dB
MASK MARGIN = 18%
Maxim Integrated
100ps/div
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
5
MAX3643
155Mbps to 2.5Gbps Burst-Mode Laser Driver
Typical Operating Characteristics (continued)
(Typical values are at VCC = 3.3V, TA = +25°C, data pattern = 27-1 PRBS + 80 ones + 27-1 PRBS + 80 zeros, unless otherwise
noted.)
RANDOM JITTER
vs. MODULATION AMPLITUDE
DETERMINISTIC JITTER
vs. MODULATION AMPLITUDE
1.1
1.0
RANDOM JITTER (psRMS)
24
21
18
15
12
9
MAX3643 toc08
27
DJ (psP-P)
1.2
MAX3643 toc07
30
0.9
0.8
0.7
0.6
0.5
0.4
6
3
0.3
0
0.2
10
20
50 60
40
IMOD (mA)
30
70
10
80
20
60
70
80
IBIAS vs. IBIASSET
IMOD vs. IMODSET
70
MAX3643 toc10
90
MAX3643 toc09
80
80
70
60
IBIAS (mA)
60
50
40
50
40
30
30
20
20
10
10
0
0
0
200
400
600
0
1000
800
200
400
600
800
IMODSET (μA)
IBIASSET (μA)
BIAS CURRENT MONITOR GAIN
(IBCMON/IBIAS) vs. TEMPERATURE
IMOD vs. VMSET
(RMODSET = 1kΩ)
90
MAX3643 toc11
17
80
70
IMOD (mAP-P)
16
15
14
1000
MAX3643 toc12
IMOD (mA)
50
IMOD (mA)
90
GAIN (mA/A)
40
30
60
50
40
30
20
13
10
0
12
-40
-20
0
20
40
TEMPERATURE (°C)
6
60
80
0
0.2
0.4
0.6
0.8
1.0
1.2
VMSET (V)
Maxim Integrated
MAX3643
155Mbps to 2.5Gbps Burst-Mode Laser Driver
Typical Operating Characteristics (continued)
(Typical values are at VCC = 3.3V, TA = +25°C, data pattern = 27-1 PRBS + 80 ones + 27-1 PRBS + 80 zeros, unless otherwise
noted.)
IBIAS + IMOD CURRENT
THRESHOLD vs. RIMAX
IBIAS vs. VBSET
(RBIASSET = 1kΩ)
70
IBIAS (mA)
60
50
40
30
20
MAX3643 toc14
80
MAX3643 toc15
160
140
CURRENT THRESHOLD (mA)
MAX3643 toc13
90
TIMING DIAGRAM, BURST-ON
(933MHz FILTER ON OUT+)
VOUT+
120
100
VBIAS+
80
60
VBEN+
40
20
10
0
0
0
0.2
0.4
0.6
0.8
0
1.0
5
10
15
20
25
30
500ps/div
RIMAX (kΩ)
VBSET (V)
SAMPLE/HOLD
(10MΩ LOAD, 2.8μs SAMPLE
AND 100μs HOLD, MDIN = 1.56V)
TIMING DIAGRAM, BURST-OFF
(933MHz FILTER ON OUT+)
MAX3643 toc17
MAX3643 toc16
VOUT+
1.56V
MDOUT
1.22V
VBIAS+
BEN+
VBEN+
500ps/div
Maxim Integrated
20μs/div
7
MAX3643
155Mbps to 2.5Gbps Burst-Mode Laser Driver
Pin Description
PIN
NAME
1
VCCA
2
IN+
Noninverted Data Input, LVPECL Compatible
3
IN-
Inverted Data Input, LVPECL Compatible
Analog Supply Voltage
4
VCCS
5
BEN+
Noninverted Burst-Enable Input, LVPECL Compatible
6
BEN-
Inverted Burst-Enable Input, LVPECL Compatible
7
BENOUT
8
EN
9
BCMON
Signal Supply Voltage
Burst-Enable Output, LVCMOS. Signal replicates BEN input.
Enable Input LVCMOS. Active low enables BIAS± and OUT± outputs.
Bias Current Monitor. Current out of this pin develops a ground-referenced voltage across an
external resistor proportional to the bias current.
10
IMAX
11
MDOUT
12
MDIN
Monitor Diode In. Analog Input for sample/hold.
13
BIAS-
Connect BIAS- to VCC Through a 10 Resistor and Switching Diode
14
BIAS+
Laser Bias Current Output. Modulation current flows into this pin when BEN input is high.
15, 18
VCCO
Output Supply Voltage
16
OUT+
Laser Modulation Current Output. Modulation current flows into this pin when both BEN and IN
inputs are high.
17
OUT-
Connect OUT- to Laser Diode Anode Through a 15 Resistor and Switching Diode
19
GND
Supply Ground. This pin must be connected to ground.
20
MODSET
21
VMSET
22
VREF
23
VBSET
24
BIASSET
—
8
FUNCTION
EP
Current-Limit Reference. Connect a resistor from IMAX to GND to set maximum IBIAS plus IMOD.
Monitor Diode Out. Analog Output for sample/hold.
Modulation Current Set. Current from this pin to ground sets the laser modulation current.
MODSET Reference. A ground-referenced voltage at this point establishes the MODSET reference.
Reference Voltage Output. May be used for VMSET, VBSET.
BIASSET Reference. A ground-referenced voltage at this point establishes the BIASSET reference.
Bias Current Set. Current from this pin to ground sets the laser bias current.
Exposed Paddle (Ground). The exposed pad must be soldered to the circuit board ground for proper
thermal and electrical operation.
Maxim Integrated
MAX3643
155Mbps to 2.5Gbps Burst-Mode Laser Driver
VCC
LP
RP
15Ω
OUT+
MAX3643
RD
OUT-
IN+
RCOMP
RD
BIAS+
CCOMP
LVPECL
IN-
BIAS-
10Ω
VCC
BEN+
LVPECL
BENCMOS
BENOUT
IMAX
LIMIT
LIMIT
VCC
VCC
MDIN
CMOS
EN
I1
IM = 88 x I1
IB = 88 x I2
I2
MDOUT
VCC
IBCMON = IB x 0.014
1.2V
RMOD
VREF
VMSET
MODSET VBSET
RBIAS
BIASSET BCMON
Figure 1. Functional Diagram
Maxim Integrated
9
MAX3643
155Mbps to 2.5Gbps Burst-Mode Laser Driver
Detailed Description
The MAX3643 laser driver includes a bias current generator, bias current monitor, modulation current generator, laser drive outputs, and monitor diode sample and
hold. LVPECL-compatible inputs are provided for both
high-speed data and burst enable. The high-speed
burst-enable input signal is replicated on an LVCMOS
output for use by the controller.
Laser Diode Modulation and
Bias Current Generators
Laser diode modulation current amplitude is controlled
by the current out of the MODSET pin, and bias current
by the current out of the BIASSET pin, according to:
IMOD = IMODSET x 88
IBIAS = IBIASSET x 88
A voltage source and two op amps are provided to
enable IMODSET and IBIASSET to be set using either a
resistor to ground or a current digital-to-analog converter (DAC). The high-impedance op amp reference input
can be externally controlled, so that the modulation and
bias currents can also be set using voltage DACs.
Laser Diode Modulation and
Bias Current Limiter
Typical laser diodes have an absolute maximum rating
of 150mA. To reduce the possibility of laser damage,
the modulation current and bias current are shut off if
the sum IMOD + IBIAS attempts to exceed the limit set
by RIMAX; see the Typical Operating Characteristics.
Bias Current Monitor
The laser diode bias current can be monitored by measuring the voltage across an external load resistor connected
from BCMON to ground. For example, a 1kΩ resistor from
BCMON to ground gives the following relationship:
VBCMON = IBIAS × GBSM × 1kΩ
The voltage at BCMON must be below 1.4V for proper
operation.
Output Drivers
The modulation current ranges from 10mA to 85mA, as
set by the current through MODSET. The laser modulation current output OUT+ is optimized to drive a 15Ω
load, and must be DC-coupled. A series damping resistor, R D , provides impedance matching to the laser
diode. The combined value of the series damping resistor and the laser diode equivalent series resistance
10
should be close to 15Ω. An RC shunt compensation
network, RCOMP/CCOMP, connected between the laser
diode cathode and ground should also be provided to
reduce optical output aberrations and duty-cycle distortion caused by laser diode parasitic inductance. The
values of RCOMP and CCOMP can be adjusted to match
the laser diode and PCB layout characteristics for optimal optical eye performance (refer to Application
Note 274: HFAN-02.0: Interfacing Maxim Laser Drivers
with Laser Diodes). The OUT- pin is connected through
a 15Ω resistor and switching diode to the laser diode
anode. The switching diode at OUT- improves the optical output eye and burst-enable delay by better matching the laser diode characteristics.
For data rates greater than 1Gbps, a parallel RL peaking network, RP/LP, connected between the laser diode
anode and VCC is recommended. This network creates
a differential drive for the laser diode to improve rise/fall
times and reduce jitter. The values of RP and LP are
also adjusted to match the laser diode and PCB layout
characteristics for optimal optical eye performance.
The bias current ranges from 1mA to 70mA, as set by
the current through BIASSET. Current in the BIAS output switches at high speed when bursting; therefore,
the BIAS+ pin should be connected directly through a
resistor, equal to RD as determined above, to the laser
cathode. The BIAS- pin is connected through a 10Ω
resistor and switching diode to VCC.
When the BEN input is high, the laser driver sinks bias
and modulation current according to the settings at
MODSET and BIASSET. When the BEN input is low, the
BIAS+ and OUT+ currents both shut off within 2ns.
Note that when BEN is low, the bias current is shunted
through the BIAS- output and the modulation current
through the OUT- output.
Monitor Diode Sample and Hold
Laser monitor diode current is only generated when
there is an optical output (BEN is active). When BEN is
inactive, the monitor current is zero, reflecting the fact
that the laser is off. A sample-and-hold circuit, triggered by the state of the BEN input, is provided in the
MAX3643. During the burst-enable active period, the
voltage present at MDIN is stored on an internal sample-and-hold capacitor; and during the burst-enable
inactive period, that voltage is output on MDOUT; see
the timing diagram in Figure 2.
While the internal sample-and-hold is sampling (BEN
active), MDOUT voltage takes a 1.2V reference level.
Maxim Integrated
MAX3643
155Mbps to 2.5Gbps Burst-Mode Laser Driver
BURST-ENABLE (BEN±) IN
≤ 125μs FOR BPON/GPON
INTERNAL MDIN VOLTAGE SAMPLER
BENOUT OUTPUT
3μs
MDOUT
< 2.56mV
1.2V
100μs
Figure 2. Sample-and-Hold Timing Diagram
Enable Input
An LVCMOS input, EN, is provided to disable both bias
and modulation currents under external control. The
maximum time to disable laser current with the EN control is 375ns.
IMOD = IMODSET x 88
To program the laser modulation current using a resistor or digital potentiometer, connect VMSET to VREF,
attach a resistor from the MODSET pin to ground, and
set the current according to:
Setting the Current Limit
A current limiter is provided to protect the laser diode
by shutting down both bias and modulation currents
when total current exceeds a value set by the resistor
connected from IMAX to ground. Do not use less than
3kΩ RIMAX. See the IBIAS + IMOD Current Threshold vs.
RIMAX graph in the Typical Operating Characteristics.
Programming the MODSET and
BIASSET Inputs
To program the laser modulation current using a current DAC, connect VMSET to VREF, attach the DAC to
the MODSET pin and set the current according to:
Maxim Integrated
IMOD =
1.2V
× 88
RMODSET + RMOD
To program the laser modulation current using a PWM
voltage DAC (requiring a high-impedance load), attach
a DAC output to the VMSET pin, connect a resistor from
the MODSET pin to ground as shown in the Typical
Applications Circuit, and set the current according to:
IMOD =
VDAC
× 88
RMODSET + RMOD
11
MAX3643
155Mbps to 2.5Gbps Burst-Mode Laser Driver
This approach can also be used for a conventional voltage DAC output, if desired. In all cases, the voltage at
MODSET must be kept ≤ 1.4V, which limits the range of
acceptable values for RMODSET depending on the maximum modulation current.
VCC
130Ω
Laser diode bias current is set in the same manner as
modulation current.
LVPECL Data/Burst-Enable Inputs
MAX3643
ZO = 50Ω
IN+/BEN+
ZO = 50Ω
IN-/BEN-
LVPECL
The MAX3643 data and BEN inputs are biased with an
on-chip, high-impedance network. When DC-coupled,
the MAX3643 operates properly with signals that meet
the EC table input-swing and common-mode requirements, including LVPECL and most CML.
See Figure 3 for a termination network that can be used
to connect the data and BEN inputs to LVPECL data outputs. Other termination networks may also be used, as
long as both the input swing and common limits are met.
130Ω
82Ω
82Ω
Figure 3. LVPECL High-Speed Inputs
Sample-and-Hold Operation
When the MAX3643 internal sample-and-hold is not
required, the MDIN pin should be connected to ground
and the MDOUT pin unconnected. If the internal sampleand-hold is required, then it is necessary to ensure that
the time constant resulting from the monitor diode load
resistance and the total load capacitance is compatible
with the desired minimum burst interval. It is also necessary to make certain that the load at MDOUT does not
exceed the capability of the MDOUT pin.
Because the voltage at MDIN is not reflected to MDOUT
until after the end of the laser burst, systems using the
internal sample-and-hold alone cannot support continuous mode operation, often a required feature for module
calibration. In this case, the voltage at MDIN can also
be connected directly to a controller mux input. As long
as the total capacitance (including monitor diode intrinsic capacitance, MDIN capacitance, mux off-capacitance, and wiring parasitics) is less than 50pF, and the
monitor diode load resistor is less than 2kΩ, then the
sample-and-hold captures a 576ns minimum burst. The
MAX3643 typical MDIN capacitance is 5pF, typical
monitor diode maximum capacitance is 25pF, and the
typical capacitance of a mux input in the off-state is
3pF to 5pF. When the mux is in the on-state, the capacitance at the input is typically 10pF to 20pF.
12
IN+
INVCMBEN + (100mV to 800mV)
VCMBEN
BEN+
VCMBEN - (100mV to 800mV)
3.3V
BENR1 = 1.65kΩ
MAX3643
VCMBEN = +2.0V
R2 = 2.54kΩ
Figure 4. Single-Ended Biasing for Burst Enable
If the minimum burst duration is longer than 576ns, it
may be useful to connect an external capacitor in parallel with the monitor diode load to limit the effects of
the data pattern on the monitor diode output.
Maxim Integrated
MAX3643
155Mbps to 2.5Gbps Burst-Mode Laser Driver
Applications Information
Running Burst-Enable Single-Ended
VCC
See Figure 5 for setting up the single-ended LVTTL or
LVCMOS biasing for burst enable.
Layout Considerations
To minimize inductance, keep the connections
between the MAX3643 output pins and laser diode as
close as possible. Place a bypass capacitor as close
as possible to each VCC connection. Take extra care
to minimize stray parasitic capacitance on the BIAS
and MDIN pins. Use good high-frequency layout techniques and multilayer boards with uninterrupted
ground planes to minimize EMI and crosstalk.
IN-
R3 = 5kΩ
LVTTL OR LVCMOS HIGH
IN+
BEN+
R4 = 3kΩ
LVTTL OR LVCMOS LOW
VCC
BENR5 = 5kΩ
MAX3643
R6 = 9kΩ
Laser Safety and IEC 825
Using the MAX3643 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 user must determine the level of
fault tolerance required by the application, recognizing
that Maxim products are neither designed nor 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 in which
the failure of a Maxim product could create a situation
where personal injury or death can occur.
Figure 5. Single-Ended LVCMOS or LVTTL Biasing for Burst
Enable
Interface Model
VCC
VCC
VCC
Exposed-Paddle Package
The exposed paddle on the 24-pin TQFN provides a
very low thermal resistance path for heat removal from
the IC. The pad is also electrical ground on the
MAX3643 and must be soldered to the circuit board
ground for proper thermal and electrical performance.
Refer to Maxim Application Note 862: HFAN-08.1:
Thermal Considerations of QFN and Other ExposedPaddle Packages for additional information.
16kΩ
5kΩ
IN+/BEN+
VCC
5kΩ
IN-/BEN-
24kΩ
MAX3643
Figure 6. Simplified Input Circuit Schematic
Maxim Integrated
13
MAX3643
155Mbps to 2.5Gbps Burst-Mode Laser Driver
Pin Configuration
TRANSISTOR COUNT: 2771
PROCESS: SiGe BiPOLAR
BIAS-
OUT+
16
VCCO
OUT17
BIAS+
VCCO
TOP VIEW
18
15
14
13
GND 19
Package Information
12 MDIN
MODSET 20
11 MDOUT
VMSET 21
10 IMAX
MAX3643
VREF 22
9
BCMON
VBSET 23
8
EN
7
BENOUT
*EP
IN-
4
5
6
BEN-
3
VCCS
2
BEN+
1
IN+
+
VCCA
BIASSET 24
Chip Information
For the latest package outline information and land patterns,
go to www.maximintegrated.com/packages. Note that a “+”,
“#”, or “-” in the package code indicates RoHS status only.
Package drawings may show a different suffix character, but
the drawing pertains to the package regardless of RoHS status.
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND
PATTERN NO.
24 TQFN-EP
T2444-3
21-0139
90-0021
THIN QFN (4mm x 4mm)
*THE EXPOSED PAD MUST BE CONNECTED TO GROUND FOR PROPER
THERMAL AND ELECTRICAL PERFORMANCE.
14
Maxim Integrated
MAX3643
155Mbps to 2.5Gbps Burst-Mode Laser Driver
Revision History
REVISION
NUMBER
REVISION
DATE
0
11/05
1
10/08
DESCRIPTION
Initial release.
Added “155Mbps to 2.5Gbps” to the data sheet/part title.
PAGES
CHANGED
—
All
Updated the Applications section.
1
In the Operating Conditions table, changed the data rate from 1250Mbps to 2500Mbps.
2
In the Typical Operating Characteristics, added the Electrical Eye Diagram graph.
6
2
7/10
Replaced the Typical Application Circuit; added the soldering temperature to the Absolute
Maximum Ratings section; updated the optical eye mask margins in the Electrical
Characteristics table; corrected equation in Note 14; added the optical eye diagrams to
the Typical Operating Characteristics section; updated the pin descriptions for the pins
with diodes (13, 17) in the Pin Description table; updated Figure 1; updated the Output
Drivers section; updated the Layout Considerations section; added the land pattern
number to the Package Information table.
3
5/12
Updated Typical Application Circuit, Electrical Characteristics table, and Typical
Operating Characteristics global conditions, and added bias current overshoot parameter
4
12/12
Updated Note 1 in the Electrical Characteristics
1, 2, 4–10,
12, 13, 14
1–7
4
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent
licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and
max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000
© 2012 Maxim Integrated Products, Inc.
15
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.