Maxim MAX3643ETG Burst-mode laser driver Datasheet

19-3848; Rev 0; 11/05
Burst-Mode Laser Driver
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-and-hold 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.
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.
♦ 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
TEMP RANGE
PINPACKAGE
MAX3643ETG
-40°C to +85°C
24 TQFN-EP*
T2444-3
MAX3643ETG+
-40°C to +85°C
24 TQFN-EP*
T2444-3
PART
PKG
CODE
*EP = Exposed paddle.
+Denotes lead-free package.
Applications
Pin Configuration appears at end of data sheet.
155/622/1244Mbps A/B/GPON ONT Modules
1.25Gbps IEEE EPON ONT Modules
Typical Application Circuit
+3.3V
0.1µF
24Ω
27nH
15Ω
+3.3V
FILTER
VCC
OUT10Ω
IN+
OUT+
IN-
BIAS+
10Ω
MAX3643
15Ω
BEN+
BIAS-
BEN-
3kΩ
VCC
CCOMP
MDIN
EN
IMAX
RCOMP
MDOUT
BCMON
1kΩ
VREF
VMSET
MODSET
1kΩ
VBSET
1kΩ
BIASSET BENOUT GND
1kΩ
ANALOG OUT
START CONVERT
ANALOG OUT
ANALOG IN
ANALOG IN
ANALOG IN
CONTROL
CONTROLLER
CONTINUOUS
OPERATION
________________________________________________________________ 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
MAX3643
General Description
MAX3643
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, BIASMON ................-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
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%
Ambient Temperature
MIN
TYP
MAX
UNITS
0.001
1000
ms
-40
+85
°C
1250
Mbps
Data Rate
Voltage at VMSET, VBSET
0
1.4
V
Voltage at BIASMON
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
ICC
Excluding laser bias and mode currents,
max at IMOD = 85mA, IBIAS = 70mA
LVPECL Differential Input Voltage
VIN
VIN = (VIN+) - (VIN-)
LVPECL Common-Mode Input
Voltage
VCM
Supply Current
MIN
TYP
MAX
UNITS
32
51
mA
1600
mVP-P
VCC VIN / 4
V
I/O SPECIFICATIONS
LVCMOS Output High Voltage
VCC 1.49
IOH = -100µA
LVCMOS Output Low Voltage
IOL = 100µA
BENOUT Propagation Delay
CL = 20pF, from BEN zero crossing to 67%
CMOS level
Td
200
LVCMOS Input Pullup Resistance
VCC 1.32
VCC 0.2
V
0.2
30
ns
75
LVCMOS Input Current
V
kΩ
VIN = 0V or VIN = VCC
50
µA
LVCMOS Input High Voltage
2.0
VCC
V
LVCMOS Input Low Voltage
0.2
0.8
V
1
70
mA
50
µA
mA/mA
BIAS GENERATOR SPECIFICATIONS
Bias Current Range
Bias Current, Burst Off
BIASSET Current Gain
2
IBIAS
IBIAS, OFF
GBIAS
VBIAS+, VBIAS- ≥ 0.6V
BEN = low or EN = high
5
1mA ≤ IBIAS < 2mA, VBSET = VREF
88
2mA ≤ IBIAS < 10mA, VBSET = VREF
70
88
110
10mA ≤ IBIAS < 70mA, VBSET = VREF
82.5
88
94.5
_______________________________________________________________________________________
Burst-Mode Laser Driver
(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
11
1mA ≤ IBIAS < 5mA
Bias Current Monitor Gain
Stability
BIASSET Resistor
2mA ≤ IBIAS ≤ 70mA, VBSET = VREF
5mA ≤ IBIAS ≤ 70mA
14
±4
-5
RBIAS
40
IMOD
10
%
+5
50
60
Ω
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
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
94.5
mA/mA
0.5
IMODSET = IBIASSET = 0.15mA
1.7
IMODSET = IBIASSET = 0.4mA
1
IMODSET = IBIASSET = 0.55mA
%
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
Ω
1.4
V
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
±5
mV
1.5
µA
TURN-OFF/-ON SPECIFICATIONS
Burst-Enable Time
(Notes 2, 6, 7)
2.3
ns
Burst-Disable Time
(Notes 2, 6, 8)
2.0
ns
_______________________________________________________________________________________
3
MAX3643
ELECTRICAL CHARACTERISTICS (continued)
MAX3643
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
2.56
V
SAMPLE/HOLD SPECIFICATIONS
MDIN Voltage Range
0.05
MDOUT Settling
Relative to final value at 3µs, CL < 20pF
Sample/Hold Droop
After 100µs (Note 9)
Sampling Error
Final value measured after 10µs
(MDOUT - MDIN), burst width > 576ns
±1
mV
±2.56
mV
3
±14
mV
1.235
1.295
V
µs
BANDGAP VOLTAGE REFERENCE SPECIFICATIONS
VREF Output
RL > 10kΩ, CL < 50pF
1.175
MODULATION/BIAS CURRENT DISABLE
Enable Time
5mA < IBIAS, 10mA < IMOD (Note 10)
5.5
Disable Time
(Notes 2, 11)
375
ns
15
kΩ
mA
RIMAX Range
Current Limit (Tested with IBIAS =
IMOD)
3
IBIAS+IMOD
RIMAX = 3kΩ
155
RIMAX = 5kΩ
100
150
RIMAX = 10kΩ
50
75
OPTICAL EVALUATION
Eye Margin
1.25Gbps (Note 12)
33
%
Note 1: DC parameters are production tested at TA = +25°C, guaranteed by design and characterization at TA = -40°C.
AC parameters are guaranteed by design and characterization.
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 SXT5731-Q 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
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
_______________________________________________________________________________________
Burst-Mode Laser Driver
OPTICAL EYE DIAGRAM
(1.25Gbps, 933MHz FILTER,
PATTERN 213-1 + 80 CID)
SUPPLY CURRENT vs. TEMPERATURE
(IBIAS = 20mA, IMOD = 30mA)
27
24
45
21
40
18
DJ (psP-P)
ICC (mA)
50
35
30
25
6
15
3
0
-40
-20
0
20
40
60
10
80
20
30
TEMPERATURE (°C)
AVERAGE OPTICAL POWER = 3dBm
EXTINCTION RATIO = 15dB
GbE MASK MARGIN = 33%
RANDOM JITTER
vs. MODULATION AMPLITUDE
50 60
40
IMOD (mA)
70
80
IMOD vs. IMODSET
1.1
1.0
MAX3643 toc05
90
MAX3643 toc04
1.2
80
70
0.9
60
0.8
IMOD (mA)
0.7
0.6
50
40
30
0.5
0.4
20
0.3
10
0
0.2
10
20
30
40
50
60
70
0
80
200
400
600
IMOD (mA)
IMODSET (µA)
IBIAS vs. IBIASSET
IMOD vs. VMSET
(RMODSET = 1kΩ)
90
MAX3643 toc06
90
80
70
80
70
IMOD (mAP-P)
60
50
40
800
1000
MAX3643 toc07
RANDOM JITTER (psRMS)
12
9
10
IBIAS (mA)
15
20
EXCELIGHT SXT5731-Q LASER
MAX3643 toc03
EXCLUDES BIAS AND
MODULATION CURRENT
55
30
MAX3643 toc02
MAX3643 toc01
60
DETERMINISTIC JITTER
vs. MODULATION AMPLITUDE
60
50
40
30
30
20
20
10
10
0
0
0
200
400
600
IBIASSET (µA)
800
1000
0
0.2
0.4
0.6
0.8
1.0
1.2
VMSET (V)
_______________________________________________________________________________________
5
MAX3643
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.)
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.)
BIAS CURRENT MONITOR GAIN
(IBCMON/IBIAS) vs. TEMPERATURE
IBIAS vs. VBSET
(RBIASSET = 1kΩ)
70
MAX3643 toc09
80
TIMING DIAGRAM, BURST-ON
(933MHz FILTER ON OUT+)
MAX3643 toc10
17
MAX3643 toc08
90
16
VOUT+
GAIN (mA/A)
60
IBIAS (mA)
50
40
15
VBIAS+
14
30
VBEN+
20
13
10
0
12
0.2
0.4
0.6
0.8
1.0
-40
-20
0
20
40
60
80
VBSET (V)
TEMPERATURE (°C)
TIMING DIAGRAM, BURST-OFF
(933MHz FILTER ON OUT+)
SAMPLE/HOLD
(10MΩ LOAD, 2.8µs SAMPLE
AND 100µs HOLD, MDIN = 1.56V)
MAX3643 toc11
500ps/div
IBIAS + IMOD CURRENT
THRESHOLD vs. RIMAX
MAX3643 toc12
160
VOUT+
MAX3643 toc13
0
140
1.56V
MDOUT
1.22V
VBIAS+
BEN+
VBEN+
CURRENT THRESHOLD (mA)
MAX3643
Burst-Mode Laser Driver
120
100
80
60
40
20
0
500ps/div
20µs/div
0
5
10
15
RIMAX (kΩ)
6
_______________________________________________________________________________________
20
25
30
Burst-Mode Laser Driver
PIN
NAME
FUNCTION
1
VCCA
2
IN+
Noninverted Data Input, LVPECL Compatible
3
IN-
Inverted Data Input, LVPECL Compatible
4
VCCS
Signal Supply Voltage
5
BEN+
Noninverted Burst-Enable Input, LVPECL Compatible
6
BEN-
Inverted Burst-Enable Input, LVPECL Compatible
7
BENOUT
8
EN
9
BCMON
10
IMAX
11
MDOUT
12
MDIN
Monitor Diode In. Analog Input for sample/hold.
13
BIAS-
Connect BIAS- to VCC Through a 15Ω Resistor (or 5Ω Resistor and Switching Diode)
Analog Supply Voltage
Burst-Enable Output, LVCMOS. Signal replicates BEN input.
Enable Input LVCMOS. Active low enables BIAS± and MOD± outputs.
Bias Current Monitor. Current out of this pin develops a ground-referenced voltage across an external
resistor proportional to the bias current.
Current-Limit Reference. Connect a resistor from IMAX to GND to set maximum IBIAS plus IMOD.
Monitor Diode Out. Analog Output for sample/hold.
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 VCC Through a 15Ω Resistor (or 5Ω 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
EP
EP
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.
_______________________________________________________________________________________
7
MAX3643
Pin Description
MAX3643
Burst-Mode Laser Driver
VCC
0.1µF
27nH
24Ω
15Ω
OUT+
MAX3643
OUT-
IN+
10Ω
RCOMP
10Ω
BIAS+
VCC
LVPECL
BIAS-
IN-
15Ω
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
8
_______________________________________________________________________________________
CCOMP
Burst-Mode Laser Driver
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.
tion current output OUT+ is optimized to drive a 15Ω
load, and must be DC-coupled. A damping resistor,
RD, provides impedance matching to the laser diode.
The combined value of the series damping resistor and
the laser diode equivalent series resistance should be
close to 15Ω. An RC shunt network, RCOMP/CCOMP,
should also be provided to reduce optical output aberrations and duty-cycle distortion. The values of RCOMP
and CCOMP can be adjusted to match the laser and PC
board layout characteristics for optimal optical eye performance. The OUT- pin is normally connected through
a 15Ω resistor to VCC or through a switching diode and
series resistor to VCC. With some laser diodes, the use
of a switching diode at OUT can improve the optical
output eye by better matching the laser characteristics.
The bias current ranges from 1mA to 70mA, as set by
the current through BIASSET. Current in the BIAS output also 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 must also be connected through a 15Ω resistor or through a switching diode
and series resistor 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.
Bias Current Monitor
Monitor Diode Sample and Hold
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:
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.
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 modula-
_______________________________________________________________________________________
9
MAX3643
Detailed Description
MAX3643
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 IMAX. 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:
10
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
______________________________________________________________________________________
Burst-Mode Laser Driver
VCC
130Ω
Laser diode bias current is set in the same manner as
modulation current.
LVPECL Data/Burst-Enable Inputs
130Ω
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.
MAX3643
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.
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 mux input as shown in the
Typical Applications Circuit. 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
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
mux is in the on-state, the capacitance at the input is
typically 10pF to 20pF.
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.
______________________________________________________________________________________
11
MAX3643
Burst-Mode Laser Driver
Applications Information
Running Burst-Enable Single-Ended
Layout Considerations
To minimize inductance, keep the connections
between the MAX3643 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. Take extra care to minimize
stray parasitic capacitance on the BIAS and MD pins.
Use good high-frequency layout techniques and multilayer boards with uninterrupted ground planes to minimize EMI and crosstalk.
IN+
VCC
See Figure 5 for setting up the single-ended LVTTL or
LVCMOS biasing for burst enable.
IN-
R3 = 5kΩ
LVTTL OR LVCMOS HIGH
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
16kΩ
5kΩ
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 HFAN-08.1: Thermal
Considerations for QFN and Other Exposed-Paddle
Packages for additional information.
IN+/BEN+
VCC
5kΩ
IN-/BEN-
24kΩ
MAX3643
Figure 6. Simplified Input Circuit Schematic
12
______________________________________________________________________________________
Burst-Mode Laser Driver
Chip Information
TRANSISTOR COUNT: 2771
PROCESS: SiGe BiPOLAR
16
BIAS-
17
VCCO
OUT+
18
BIAS+
VCCO
OUT-
TOP VIEW
15
14
13
12 MDIN
GND 19
11 MDOUT
MODSET 20
10 IMAX
VMSET 21
MAX3643
VREF 22
VBSET 23
*EP
IN-
4
5
6
BEN-
3
VCCS
2
BEN+
1
IN+
+
VCCA
BIASSET 24
9
BCMON
8
EN
7
BENOUT
THIN QFN (4mm x 4mm)
*THE EXPOSED PAD MUST BE CONNECTED TO GROUND FOR PROPER
THERMAL AND ELECTRICAL PERFORMANCE.
______________________________________________________________________________________
13
MAX3643
Pin Configuration
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.)
24L QFN THIN.EPS
MAX3643
Burst-Mode Laser Driver
PACKAGE OUTLINE,
12, 16, 20, 24, 28L THIN QFN, 4x4x0.8mm
21-0139
14
______________________________________________________________________________________
E
1
2
Burst-Mode Laser Driver
PACKAGE OUTLINE,
12, 16, 20, 24, 28L THIN QFN, 4x4x0.8mm
21-0139
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 15
© 2005 Maxim Integrated Products
M. QUIJANO
Printed USA
is a registered trademark of Maxim Integrated Products, Inc.
MAX3643
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.)
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