MAX3643_08 [MAXIM]
155Mbps to 2.5Gbps Burst-Mode Laser Driver; 155Mbps至2.5Gbps的突发模式激光驱动器
| 型号： | MAX3643_08 |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | 155Mbps to 2.5Gbps Burst-Mode Laser Driver |
| 文件： | 总14页 (文件大小：244K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-3848; Rev 1; 10/08
155Mbps to 2.5Gbps Burst-Mode Laser Driver
MAX643
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 (out-
put off) condition to full on-condition in less than 2ns.
When BEN is inactive, typical modulation and bias cur-
rents are 5µA each.
♦ 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
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.
♦ LVPECL High-Speed Inputs (Data, Burst Enable)
Ordering Information
PART
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
24 TQFN-EP*
24 TQFN-EP*
MAX3643ETG
MAX3643ETG+
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.
+Denotes a lead-free/RoHS-compliant package.
*EP = Exposed paddle.
Applications
A/B/GPON 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
0.1μF
24Ω
27nH
15Ω
+3.3V
FILTER
V
CC
OUT-
OUT+
BIAS+
10Ω
10Ω
15Ω
IN+
IN-
R
COMP
MAX3643
C
COMP
BEN+
BEN-
BIAS-
V
CC
MDIN
EN
MDOUT
1kΩ
IMAX BCMON
VMSET
MODSET
VBSET
BIASSET BENOUT
VREF
GND
1kΩ
3kΩ
1kΩ
1kΩ
ANALOG OUT
START CONVERT
ANALOG IN
ANALOG OUT
ANALOG IN
CONTROL
ANALOG IN
CONTINUOUS
OPERATION
CONTROLLER
________________________________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
155Mbps to 2.5Gbps Burst-Mode Laser Driver
ABSOLUTE MAXIMUM RATINGS
Supply Voltage V
..............................................-0.5V to +4.0V
Continuous Power Dissipation (T = +85°C)
A
CC
Current into BIAS-, BIAS+, OUT-, OUT+ .......-20mA to +150mA
Voltage at VMSET, VBSET, IN+, IN-, BEN+, BEN-, EN, MDIN,
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
MDOUT, BENOUT, BIASMON ................-0.5V to (V
+ 0.5V)
CC
Voltage at MODSET, BIASSET, VREF, IMAX ........-0.5V to +3.0V
Voltage at OUT-, OUT+, BIAS-, BIAS+ .....+0.3V to (V + 0.5V)
CC
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.
MAX643
OPERATING CONDITIONS
PARAMETER
Supply Turn-On Time
Ambient Temperature
Data Rate
SYMBOL
CONDITIONS
MIN
0.001
-40
TYP
MAX
1000
+85
2500
1.4
UNITS
ms
°C
10% to 90%
Mbps
V
Voltage at VMSET, VBSET
Voltage at BIASMON
Voltage at MDIN
0
0
0
1.4
V
2.56
V
ELECTRICAL CHARACTERISTICS
(V
CC
= +3.0V to +3.6V, T = -40°C to +85°C. Typical values are at V
= +3.3V, T = +25°C, I
= 20mA, I
= 30mA, unless
A
CC
A
BIAS
MOD
otherwise noted.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Excluding laser bias and mode currents,
max at I = 85mA, I = 70mA
Supply Current
I
32
51
mA
CC
MOD
BIAS
I/O SPECIFICATIONS
LVPECL Differential Input Voltage
V
V
= (V ) - (V
IN+
)
IN-
200
1600
mV
P-P
IN
IN
LVPECL Common-Mode Input
Voltage
V
1.49
-
V
1.32
-
V
-
CC
CC
CC
V
V
CM
V
/ 4
IN
V
0.2
-
CC
LVCMOS Output High Voltage
LVCMOS Output Low Voltage
BENOUT Propagation Delay
I
I
= -100µA
= 100µA
V
V
OH
OL
0.2
C = 20pF, from BEN zero crossing to 67%
L
CMOS level
T
30
ns
d
LVCMOS Input Pullup Resistance
LVCMOS Input Current
75
kΩ
µA
V
V
= 0V or V = V
IN CC
50
IN
LVCMOS Input High Voltage
LVCMOS Input Low Voltage
2.0
0.2
V
CC
0.8
V
BIAS GENERATOR SPECIFICATIONS
Bias Current Range
I
V
, V ≥ 0.6V
BIAS+ BIAS-
1
70
50
mA
µA
BIAS
Bias Current, Burst Off
I
BEN = low or EN = high
5
BIAS, OFF
1mA ≤ I
2mA ≤ I
< 2mA, VBSET = VREF
< 10mA, VBSET = VREF
88
88
88
BIAS
BIAS
BIASSET Current Gain
G
70
110
mA/mA
BIAS
10mA ≤ I
< 70mA, VBSET = VREF
82.5
94.5
BIAS
2
_______________________________________________________________________________________
155Mbps to 2.5Gbps Burst-Mode Laser Driver
MAX643
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= +3.0V to +3.6V, T = -40°C to +85°C. Typical values are at V
= +3.3V, T = +25°C, I
= 20mA, I
= 30mA, unless
A
CC
A
BIAS
MOD
otherwise noted.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
≤ 70mA (Note 13)
≤ 70mA (Note 14)
MIN
-4.4
TYP
MAX
+4.4
UNITS
%
BIASSET Current Gain Stability
BIASSET Current Gain Linearity
Bias Current Overshoot
5mA ≤ I
5mA ≤ I
BIAS
BIAS
-3.75
+3.75
10
%
V
turn-on/-off < 1s
%
CC
Bias Current Monitor Gain
G
2mA ≤ I
1mA ≤ I
5mA ≤ I
≤ 70mA, VBSET = VREF
< 5mA
11
14
4
17
mA/A
BSM
BIAS
BIAS
BIAS
Bias Current Monitor Gain
Stability
%
≤ 70mA
-5
+5
60
BIASSET Resistor
R
40
50
5
Ω
BIAS
MODULATOR SPECIFICATIONS
Modulation Current Range
Modulation Current Off
I
10
85
mA
µA
MOD
I
BEN = low or EN = high or V = low
120
MOD, OFF
IN
10mA ≤ I
60mA ≤ I
< 60mA
0.6
0.75
82.5
-4.4
-2.2
MOD
MOD
Instantaneous Voltage at OUT+
V
≤ 85mA
MODSET Current Gain
G
10mA < I
(Note 13)
(Note 14)
< 85mA, VMSET = VREF
88
0.5
94.5
+4.4
+2.2
mA/mA
MOD
MOD
MODSET Current Gain Stability
MODSET Current Gain Linearity
%
%
I
I
I
I
= 0.15mA, I
= 0.7mA
BIASSET
MODSET
MODSET
MODSET
MODSET
= I
= I
= I
= 0.15mA
= 0.4mA
= 0.55mA
1.7
1
MODSET, BIASSET Gain
Matching (Note 15)
BIASSET
BIASSET
BIASSET
%
1
Modulation Current Rise Time
Modulation Current Fall Time
Deterministic Jitter
t
20% to 80%
20% to 80%
(Note 3)
45
45
17
0.8
50
85
85
45
1.4
60
ps
ps
R
t
F
ps
P-P
RMS
Ω
Random Jitter
(Note 4)
ps
MODSET Resistor
R
40
MOD
MODSET, BIASSET OPERATIONAL AMPLIFIER SPECIFICATIONS
MODSET, BIASSET Voltage
Range
0.005
1.4
V
Voltage Error
(Note 5)
5
mV
µA
Input Leakage
VMSET and VBSET pins
0.1
1.5
TURN-OFF/-ON SPECIFICATIONS
Burst-Enable Time
Burst-Disable Time
(Notes 2, 6, 7)
(Notes 2, 6, 8)
2.3
2.0
ns
ns
_______________________________________________________________________________________
3
155Mbps to 2.5Gbps Burst-Mode Laser Driver
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= +3.0V to +3.6V, T = -40°C to +85°C. Typical values are at V
= +3.3V, T = +25°C, I
= 20mA, I
= 30mA, unless
A
CC
A
BIAS
MOD
otherwise noted.) (Note 1)
PARAMETER
SAMPLE/HOLD SPECIFICATIONS
MDIN Voltage Range
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
0.05
2.56
V
MDOUT Settling
Relative to final value at 3µs, C < 20pF
L
1
mV
mV
MAX643
Sample/Hold Droop
Sampling Error
After 100µs (Note 9)
2.56
Final value measured after 10µs
(MDOUT - MDIN), burst width > 576ns
3
14
mV
BANDGAP VOLTAGE REFERENCE SPECIFICATIONS
VREF Output
R > 10kΩ, C < 50pF
1.175
1.235
1.295
V
L
L
MODULATION/BIAS CURRENT DISABLE
Enable Time
5mA < I
, 10mA < I
(Note 10)
5.5
375
15
µs
ns
kΩ
BIAS
MOD
Disable Time
(Notes 2, 11)
R
Range
3
IMAX
R
R
R
= 3kΩ
= 5kΩ
= 10kΩ
155
100
50
IMAX
IMAX
IMAX
Current Limit (Tested with I
=
BIAS
I
+I
150
75
mA
%
BIAS MOD
I
)
MOD
OPTICAL EVALUATION
Eye Margin
1.25Gbps (Note 12)
33
Note 1: DC parameters are production tested at T = +25°C, guaranteed by design and characterization at T = -40°C.
A
A
AC parameters are guaranteed by design and characterization.
Note 2: For 10mA ≤ I
≤ 85mA and 4mA ≤ I
≤ 70mA.
MOD
BIAS
7
7
Note 3: Deterministic jitter measured with a continuous pattern of 2 -1 PRBS, 80 ones, 2 -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 V
Note 14: Gain linearity = (Gainmax – Gainmin), Gainavg = Gainmax - Gainmin
= 3.3V, T = +25°C.
A
CC
Gainavg/2
2
Note 15: Gain matching =
nominal at V
= 3.3V, T = +25°C.
CC A
Gainmod / Gainbias − Gainmodnom / Gainbiasnom
Gainmodnom / Gainbiasnom
4
_______________________________________________________________________________________
155Mbps to 2.5Gbps Burst-Mode Laser Driver
MAX643
Typical Operating Characteristics
(Typical values are at V
= +3.3V, T = +25°C, data pattern = 27-1 PRBS + 80 ones + 27-1 PRBS + 80 zeros, unless otherwise
A
CC
noted.)
OPTICAL EYE DIAGRAM
(1.25Gbps, 933MHz FILTER,
PATTERN 2 -1 + 80 CID)
DETERMINISTIC JITTER
vs. MODULATION AMPLITUDE
SUPPLY CURRENT vs. TEMPERATURE
(I = 20mA, I = 30mA)
13
BIAS
MOD
30
27
24
21
18
15
12
9
60
55
50
45
40
35
30
25
20
15
10
EXCLUDES BIAS AND
MODULATION CURRENT
6
3
0
60
10
30
50
70 80
-40 -20
0
20
40
80
20
40
I
60
EXCELIGHT SXT5731-Q LASER
(mA)
TEMPERATURE (°C)
MOD
AVERAGE OPTICAL POWER = 3dBm
EXTINCTION RATIO = 15dB
GbE MASK MARGIN = 33%
RANDOM JITTER
vs. MODULATION AMPLITUDE
I
vs. I
MOD
MODSET
90
80
70
60
50
40
30
20
10
0
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
10
0
200
400
600
800
1000
40 50
20
60
70
80
30
I
(μA)
I
(mA)
MODSET
MOD
I
(R
vs. VMSET
MOD
I
vs. I
BIAS
BIASSET
= 1kΩ)
MODSET
90
80
70
60
50
40
30
20
10
90
80
70
60
50
40
30
20
10
0
0
0
200
400
600
800
1000
0
0.2
0.4
0.6
VMSET (V)
0.8
1.0
1.2
I
(μA)
BIASSET
_______________________________________________________________________________________
5
155Mbps to 2.5Gbps Burst-Mode Laser Driver
Typical Operating Characteristics (continued)
(Typical values are at V
noted.)
= +3.3V, T = +25°C, data pattern = 27-1 PRBS + 80 ones + 27-1 PRBS + 80 zeros, unless otherwise
A
CC
BIAS CURRENT MONITOR GAIN
(I /I ) vs. TEMPERATURE
BCMON BIAS
I
(R
vs. VBSET
BIAS
TIMING DIAGRAM, BURST-ON
(933MHz FILTER ON OUT+)
= 1kΩ)
BIASSET
MAX3643 toc10
90
80
70
60
50
40
30
20
10
0
17
16
15
14
13
12
V
OUT+
MAX643
V
BIAS+
V
BEN+
0
0.2
0.4
0.6
0.8
1.0
-40
-20
0
20
40
60
80
500ps/div
VBSET (V)
TEMPERATURE (°C)
SAMPLE/HOLD
(10MΩ LOAD, 2.8μs SAMPLE
I
+ I
CURRENT
TIMING DIAGRAM, BURST-OFF
(933MHz FILTER ON OUT+)
BIAS MOD
AND 100μs HOLD, MDIN = 1.56V)
THRESHOLD vs. R
IMAX
MAX3643 toc11
MAX3643 toc12
160
140
120
100
80
V
OUT+
1.56V
MDOUT
BEN+
1.22V
V
V
BIAS+
BEN+
60
40
20
0
0
5
10
15
20
25
30
500ps/div
20μs/div
ELECTRICAL EYE DIAGRAM
(2.5Gbps, I = 30mA,
MOD
7
PATTERN = PRBS 2 - 1 + 80 CID)
MAX3643 toc14
100ps/div
6
_______________________________________________________________________________________
155Mbps to 2.5Gbps Burst-Mode Laser Driver
MAX643
Pin Description
PIN
1
NAME
FUNCTION
V
Analog Supply Voltage
CCA
2
IN+
IN-
Noninverted Data Input, LVPECL Compatible
Inverted Data Input, LVPECL Compatible
Signal Supply Voltage
3
4
V
CCS
BEN+
BEN-
5
Noninverted Burst-Enable Input, LVPECL Compatible
Inverted Burst-Enable Input, LVPECL Compatible
6
7
BENOUT
Burst-Enable Output, LVCMOS. Signal replicates BEN input.
Enable Input LVCMOS. Active low enables BIAS and MOD outputs.
8
EN
Bias Current Monitor. Current out of this pin develops a ground-referenced voltage across an external
resistor proportional to the bias current.
9
BCMON
10
11
IMAX
MDOUT
MDIN
Current-Limit Reference. Connect a resistor from IMAX to GND to set maximum I
Monitor Diode Out. Analog Output for sample/hold.
plus I
.
MOD
BIAS
12
Monitor Diode In. Analog Input for sample/hold.
13
BIAS-
Connect BIAS- to V
Through a 15Ω Resistor (or 5Ω Resistor and Switching Diode)
CC
14
BIAS+
Laser Bias Current Output. Modulation current flows into this pin when BEN input is high.
Output Supply Voltage
15, 18
V
CCO
Laser Modulation Current Output. Modulation current flows into this pin when both BEN and IN inputs
are high.
16
OUT+
17
19
20
OUT-
GND
Connect OUT- to V
Through a 15Ω Resistor (or 5Ω Resistor and Switching Diode)
CC
Supply Ground. This pin must be connected to ground.
MODSET
Modulation Current Set. Current from this pin to ground sets the laser modulation current.
21
22
23
24
VMSET
VREF
MODSET Reference. A ground-referenced voltage at this point establishes the MODSET reference.
Reference Voltage Output. May be used for VMSET, VBSET.
VBSET
BIASSET
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.
EP
EP
_______________________________________________________________________________________
7
155Mbps to 2.5Gbps Burst-Mode Laser Driver
V
CC
0.1μF
24Ω
27nH
MAX643
15Ω
OUT+
10Ω
MAX3643
OUT-
R
10Ω
COMP
IN+
BIAS+
C
COMP
V
CC
LVPECL
15Ω
BIAS-
IN-
BEN+
LVPECL
BEN-
IMAX
CMOS
BENOUT
MDIN
LIMIT
LIMIT
V
CC
V
CC
CMOS
EN
I
M
= 88 x I
I
I
= 88 x I
2
I
I
2
1
B
1
MDOUT
V
CC
= I x
B 0.014
BCMON
1.2V
R
MOD
R
BIAS
VREF
VMSET
VBSET
BIASSET BCMON
MODSET
Figure 1. Functional Diagram
8
_______________________________________________________________________________________
155Mbps to 2.5Gbps Burst-Mode Laser Driver
MAX643
tion current output OUT+ is optimized to drive a 15Ω
Detailed Description
load, and must be DC-coupled. A damping resistor,
The MAX3643 laser driver includes a bias current gen-
R , provides impedance matching to the laser diode.
D
The combined value of the series damping resistor and
the laser diode equivalent series resistance should be
erator, bias current monitor, modulation current genera-
tor, 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.
close to 15Ω. An RC shunt network, R
/C
,
COMP COMP
should also be provided to reduce optical output aber-
rations and duty-cycle distortion. The values of R
COMP
and C
can be adjusted to match the laser and PC
COMP
board layout characteristics for optimal optical eye per-
formance. The OUT- pin is normally connected through
Laser Diode Modulation and
Bias Current Generators
a 15Ω resistor to V
or through a switching diode and
CC
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:
series resistor to V . With some laser diodes, the use
CC
of a switching diode at OUT can improve the optical
output eye by better matching the laser characteristics.
I
I
= I
= I
x 88
x 88
MOD
BIAS
MODSET
BIASSET
The bias current ranges from 1mA to 70mA, as set by
the current through BIASSET. Current in the BIAS out-
put also switches at high speed when bursting; there-
fore, the BIAS+ pin should be connected directly
A voltage source and two op amps are provided to
enable I and I to be set using either a
MODSET
BIASSET
resistor to ground or a current digital-to-analog convert-
er (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.
through a resistor, equal to R as determined above, to
D
the laser cathode. The BIAS- pin must also be connect-
ed through a 15Ω resistor or through a switching diode
and series resistor to V
.
CC
Laser Diode Modulation and
Bias Current Limiter
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.
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 I
+ I
attempts to exceed the limit set
BIAS
; see the Typical Operating Characteristics.
MOD
by R
IMAX
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, trig-
gered 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 sam-
ple-and-hold capacitor; and during the burst-enable
inactive period, that voltage is output on MDOUT; see
the timing diagram in Figure 2.
Bias Current Monitor
The laser diode bias current can be monitored by measur-
ing 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:
V
= I
× G
×1kΩ
BCMON BIAS
BSM
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-
While the internal sample-and-hold is sampling (BEN
active), MDOUT voltage takes a 1.2V reference level.
_______________________________________________________________________________________
9
155Mbps to 2.5Gbps Burst-Mode Laser Driver
BURST-ENABLE (BEN ) IN
≤ 125μs FOR BPON/GPON
MAX643
INTERNAL MDIN VOLTAGE SAMPLER
BENOUT OUTPUT
3μs
MDOUT
< 2.56mV
1.2V
100μs
Figure 2. Sample-and-Hold Timing Diagram
I
= I
x 88
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 con-
trol is 375ns.
MOD
MODSET
To program the laser modulation current using a resis-
tor 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
1.2V
I
=
× 88
MOD
R
+R
MOD
MODSET
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:
3kΩ I
. See the I
+ I
Current Threshold vs.
MAX
BIAS
MOD
R
graph in the Typical Operating Characteristics.
IMAX
Programming the MODSET and
BIASSET Inputs
To program the laser modulation current using a cur-
rent DAC, connect VMSET to VREF, attach the DAC to
the MODSET pin and set the current according to:
V
DAC
I
=
× 88
MOD
R
+R
MODSET
MOD
10 ______________________________________________________________________________________
155Mbps to 2.5Gbps Burst-Mode Laser Driver
MAX643
This approach can also be used for a conventional volt-
V
CC
age DAC output, if desired. In all cases, the voltage at
MODSET must be kept ≤ 1.4V, which limits the range of
acceptable values for R
depending on the maxi-
MODSET
mum modulation current.
MAX3643
130Ω
82Ω
130Ω
82Ω
Laser diode bias current is set in the same manner as
modulation current.
Z
Z
= 50Ω
= 50Ω
IN+/BEN+
IN-/BEN-
O
LVPECL
LVPECL Data/Burst-Enable Inputs
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 require-
ments, including LVPECL and most CML.
O
See Figure 3 for a termination network that can be used
to connect the data and BEN inputs to LVPECL data out-
puts. Other termination networks may also be used, as
long as both the input swing and common limits are met.
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 sample-
and-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 neces-
sary to make certain that the load at MDOUT does not
exceed the capability of the MDOUT pin.
IN+
IN-
V
V
+ (100mV to 800mV)
- (100mV to 800mV)
CMBEN
CMBEN
BEN+
V
CMBEN
3.3V
BEN-
R = 1.65kΩ
1
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 continu-
ous 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 capaci-
tance (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 maxi-
mum capacitance is 25pF, and the typical capacitance
of a mux input in the off-state is 3pF to 5pF. When the
MAX3643
V
= +2.0V
CMBEN
R = 2.54kΩ
2
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 par-
allel with the monitor diode load to limit the effects of
the data pattern on the monitor diode output.
______________________________________________________________________________________ 11
155Mbps to 2.5Gbps Burst-Mode Laser Driver
Applications Information
IN+
Running Burst-Enable Single-Ended
See Figure 5 for setting up the single-ended LVTTL or
LVCMOS biasing for burst enable.
V
CC
IN-
R = 5kΩ
3
LVTTL OR LVCMOS HIGH
LVTTL OR LVCMOS LOW
Layout Considerations
To minimize inductance, keep the connections
between the MAX3643 output pins and laser diode as
close as possible. Optimize the laser diode perfor-
mance by placing a bypass capacitor as close as pos-
sible 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 multi-
layer boards with uninterrupted ground planes to mini-
mize EMI and crosstalk.
BEN+
R = 3kΩ
4
V
CC
MAX643
BEN-
R = 5kΩ
5
MAX3643
R = 9kΩ
6
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 sup-
port 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
V
CC
V
CC
V
CC
16kΩ
5kΩ
5kΩ
IN+/BEN+
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.
V
CC
IN-/BEN-
24kΩ
MAX3643
Figure 6. Simplified Input Circuit Schematic
12 ______________________________________________________________________________________
155Mbps to 2.5Gbps Burst-Mode Laser Driver
MAX643
Pin Configuration
Chip Information
TRANSISTOR COUNT: 2771
TOP VIEW
PROCESS: SiGe BiPOLAR
Package Information
18 17 16 15 14 13
For the latest package outline information and land patterns, go
19
12
GND
MDIN
to www.maxim-ic.com/packages.
MODSET 20
11 MDOUT
PACKAGE TYPE PACKAGE CODE DOCUMENT NO.
21
22
23
24
10
9
VMSET
VREF
IMAX
24 TQFN-EP
T2444-3
21-0139
MAX3643
BCMON
VBSET
EN
8
*EP
BIASSET
BENOUT
7
+
1
2
3
4
5
6
THIN QFN (4mm x 4mm)
*THE EXPOSED PAD MUST BE CONNECTED TO GROUND FOR PROPER
THERMAL AND ELECTRICAL PERFORMANCE.
______________________________________________________________________________________ 13
155Mbps to 2.5Gbps Burst-Mode Laser Driver
Revision History
REVISION REVISION
PAGES
CHANGED
DESCRIPTION
NUMBER
DATE
0
11/05
Initial release.
—
All
1
Added “155Mbps to 2.5Gbps” to the data sheet/part title.
Updated the Applications section.
MAX643
In the Operating Conditions table, changed the data rate from 1250Mbps to
2500Mbps.
1
10/08
2
6
In the Typical Operating Characteristics, added the ELECTRICAL EYE DIAGRAM
graph.
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.
14 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2008 Maxim Integrated Products
is a registered trademark of Maxim Integrated Products, Inc.
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