MAXIM MAX3741ETE

19-2597; Rev 1; 5/04
3.2Gbps Compact SFP VCSEL Driver
The MAX3741 is a high-speed VCSEL driver for smallform-factor (SFF) and small-form-factor pluggable (SFP)
fiber-optic LAN transmitters. It contains a bias generator,
laser modulator, and peaking current option to improve
VCSEL edge speed. The driver accommodates common
cathode and differential configurations.
The MAX3741 operates up to 3.2Gbps. It can switch up
to 15mA of laser modulation current and source up to
15mA of bias current. The MAX3741 is designed to interface with a digital potentiometer and control circuitry.
The MAX3741 accommodates various VCSEL packages,
including low-cost TO-46 headers.
The MAX3741 is available in a compact 3mm x 3mm
16-pin thin QFN package and operates over a temperature range of -40°C to +85°C.
Features
♦ 2mA to 15mA Modulation Current
♦ 1mA to 15mA Bias Current
♦ Optional Peaking Current to Improve VCSEL Edge
Speed
♦ Supports Common Cathode and Differential
Configuration
♦ 3mm × 3mm 16-Pin Thin QFN Package
Applications
Ordering Information
Multirate (1Gbps to 3.2Gbps) SFP/SFF Modules
Gigabit Ethernet Optical Transmitters
Fibre Channel Optical Transmitters
PART
TEMP
RANGE
PINPACKAGE
PKG.
CODE
MAX3741ETE
-40°C to +85°C
16 Thin QFN
T1633F-3
Pin Configuration
Typical Application Circuit
+3.3V
0.1µF
L1*
IN+
TX_DISABLE
1
IN+
2
BIASSET
BIAS
BIAS
VCC
TOP VIEW
VCC
GND
0.01µF
16
15
14
13
12 BIASMON
0.01µF
11 OUT+
MAX3741
3mm x 3mm
0.01µF
OUT50Ω
BIASMON
BIASSET
RBIASSET
MODSET
RMODSET
GND PEAKSET
RPEAKSET
3
N.C.
4
5
RMON
10 OUT9
VCC
TX_DISABLE
IN-
6
7
8
GND
OUT+
PEAKSET
MAX3741
MODSET
IN0.1µF
VCC
THIN QFN
EXPOSED PAD IS CONNECTED TO GND.
THIS SYMBOL REPRESENTS A TRANSMISSION LINE OF
CHARACTERISTIC IMPEDANCE Zo = 50Ω.
* FERRITE BEAD, MURATA BLM18HD102SN1B
________________________________________________________________ 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
MAX3741
General Description
MAX3741
3.2Gbps Compact SFP VCSEL Driver
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (VCC) ............................................-0.5V to +5.0V
Voltage at TX_DISABLE, IN+, IN-, MODSET,
PEAKSET, BIASSET, BIAS, BIASMON .......-0.5V to (VCC + 0.5V)
Voltage at OUT+, OUT- .........................(VCC - 2V) to (VCC + 2V)
Current into OUT+, OUT- ....................................................60mA
Continuous Power Dissipation (TA = +85°C)
16-Lead Thin QFN (derate 25mW/°C above +85°C) ..........2W
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.
ELECTRICAL CHARACTERISTICS
(VCC = +2.97V to +3.63V, TA = -40°C to +85°C. Typical values are at VCC = +3.3V, TA = +25°C, unless otherwise noted.)
PARAMETER
Supply Current
SYMBOL
ICC
ICC-SHDW
CONDITIONS
TX_DISABLE set low,
peaking is not used
(Note 1)
MIN
TYP
MAX
IMOD = 2mAP-P
41
IMOD = 15mAP-P
51
65
Additional current when peaking is used
(Note 2)
14
20
Total current when TX_DISABLE is high
0.15
1
UNITS
mA
TX_DISABLE INPUT
Input Impedance
80
Input High Voltage
VIH
Input Low Voltage
VIL
t_off
TX_DISABLE Time
t_on
Input Leakage
105
kΩ
2
V
0.8
Time from rising edge of TX_DISABLE to
IBIAS = IBIAS_OFF and IMOD = IMOD_OFF
(Note 3)
0.2
Time from falling edge of TX_DISABLE to
IBIAS = 15mA and IMOD = 15mAP-P
111
VCC = 0V and VTX_DISABLE = 3.3V
25
V
3
µs
40
µA
BIAS GENERATOR (Note 4)
Bias Current
Accuracy of Programmed Bias
Current
Bias Current During Disable
IBIAS
Min
Max
∆IBIAS
IBIAS_OFF
1
15
-8
+8
TX_DISABLE high
BIASMON Gain
0.095
0.115
mA
%
10
µA
0.135
mA/mA
2200
mVP-P
80
Ω
LASER MODULATOR (Note 5)
Data Input Voltage Swing
Output Resistance
Modulation Current
2
VID
ROUT
IMOD
Total differential signal
250
Single-ended resistance at OUT+, OUT-
63
Min
Max
2
15
_______________________________________________________________________________________
mAP-P
3.2Gbps Compact SFP VCSEL Driver
MAX3741
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +2.97V to +3.63V, TA = -40°C to +85°C. Typical values are at VCC = +3.3V, TA = +25°C, unless otherwise noted.)
PARAMETER
SYMBOL
Programmable Peaking Current
IPEAK
CONDITIONS
MIN
TYP
Min
0.2
Max
2
Peaking Current Duration
MAX
mA
80
Tolerance of Programmed
Modulation Current
ps
-10
Modulation Transition Time
tR, tF
UNITS
+10
%
ps
5mAP-P ≤ IMOD ≤ 15mAP-P (Note 3)
65
95
Deterministic Jitter
DJ
5mAP-P ≤ IMOD ≤ 15mAP-P (Notes 3, 6)
13
25
psP-P
Random Jitter
RJ
(Note 3)
1
4
psRMS
15
50
µAP-P
100
115
Ω
Laser Modulation During Disable
IMOD_OFF
Differential input voltage at 2200mVP-P
Differential Input Resistance
85
Input Bias Voltage
Note 1:
Note 2:
Note 3:
Note 4:
Note 5:
Note 6:
VCC 0.3
VIN
V
Measured with RBIASSET = 1.87kΩ (IBIAS ≈ 15mA). Supply current excludes IBIAS.
Tested with RPEAK = 1.18kΩ.
Guaranteed by design and characterization.
VBIAS is less than VCC - 0.7V.
Measured electrically with a 50Ω load AC-coupled to OUT+.
Deterministic jitter is the peak-to-peak deviation from the ideal time crossings measured with a K28.5 bit pattern at 3.2Gbps
(00111110101100000101).
Typical Operating Characteristics
(VCC = +3.3V, TA = 25°C, measured electrically with a 50Ω load AC-coupled to OUT+, unless otherwise noted.)
ELECTRICAL EYE
ELECTRICAL EYE WITH PEAKING
MAX3741 toc01
3.2Gbps, K28.5, 10mA
MODULATION, NO PEAKING
87mV/div
MAX3741 toc03
3.2Gbps, K28.5, 10mA
MODULATION, RPEAKSET = 2.4kΩ
87mV/div
50ps/div
ELECTRICAL EYE WITH PEAKING
MAX3741 toc02
3.2Gbps, K28.5, 10mA
MODULATION, RPEAKSET = 500Ω
87mV/div
50ps/div
50ps/div
_______________________________________________________________________________________
3
Typical Operating Characteristics (continued)
(VCC = +3.3V, TA = 25°C, measured electrically with a 50Ω load AC-coupled to OUT+, unless otherwise noted.)
OPTICAL EYE
AT 2.125Gbps
OPTICAL EYE
DETERMINISTIC JITTER vs. IMOD
MAX3741 toc05
28
(ER = 8.8dB, 1.063Gbps, K28.5, 850nm VCSEL, WITH
2.3GHz O-TO-E CONVERTER)
DETERMINISTIC JITTER (psP-P)
(ER = 8.8dB, K28.5, 850nm VCSEL, WITH
2.3GHz O-TO-E CONVERTER)
MAX3741 toc06
MAX3741 toc04
24
20
16
12
8
4
0
68ps/div
135ps/div
5
0
10
15
MODULATION CURRENT (mAP-P)
BIAS CURRENT vs. RBIASSET
2.0
1.5
12
10
8
6
1.0
4
0.5
2
5
IBIASMON vs. BIAS CURRENT
1.4
5
10
15
20
25
6
4
0
0.8
8
-2
-4
10
12
-6
S22 (dB)
S11 (dB)
1.0
6
0
-10
1.2
4
OUTPUT RETURN LOSS
DIFFERENTIAL
MEASUREMENT
-5
2
RMODSET (kΩ)
INPUT RETURN LOSS
0.6
-15
-20
-8
-10
-12
-14
-25
0.4
-16
-30
0.2
0
0
4
8
BIAS CURRENT (mA)
4
8
30
0
MAX3741 toc10
1.6
10
RBIASSET (kΩ)
MODULATION CURRENT (mAP-P)
1.8
12
0
0
15
10
MAX3741 toc11
0
14
2
0
0
MAX3741 toc09
14
16
MAX3741 toc12
2.5
MAX3741 toc08
MAX3741 toc07
3.0
BIAS CURRENT (mA)
RANDOM JITTER (psRMS)
3.5
IMOD vs. RMODSET
16
MODULATION CURRENT (mAP-P)
RANDOM JITTER vs. IMOD
4.0
IBIASMON (mA)
MAX3741
3.2Gbps Compact SFP VCSEL Driver
12
16
-35
100M
-18
1G
FREQUENCY (Hz)
10G
-20
100M
1G
FREQUENCY (Hz)
_______________________________________________________________________________________
10G
3.2Gbps Compact SFP VCSEL Driver
RISE TIME
65
60
FALL TIME
55
50
-4
50
40
40
-10
10
2
4
6
8
10
12
14
16
-6
-8
30
20
45
PSR = 20log ∆VOUT
∆VCC
-2
60
MAX3741 toc15
POWER-SUPPLY REJECTION
0
PSR (dB)
70
IMOD = 2mAP-P
70
SUPPLY CURRENT (mA)
TRANSITION TIME (ps)
MAX3741 toc13
MEASURED FROM
20% TO 80%
75
SUPPLY CURRENT vs. TEMPERATURE
80
MAX3741 toc14
TRANSITION TIME vs. IMOD
80
-12
-40
IMOD (mA)
-15
10
35
60
85
TEMPERATURE (°C)
100
1k
10k
100k
1M
10M
100M
FREQUENCY (Hz)
Pin Description
PIN
NAME
FUNCTION
1
TX_DISABLE
2
IN+
Noninverted Data Input
3
IN-
Inverted Data Input
4
N.C.
No Connection
5, 9, 15
VCC
+3.3V Supply Voltage
6
MODSET
Modulation Set. A resistor connected from MODSET to ground (RMODSET) programs the desired
modulation current amplitude.
7
PEAKSET
Peaking Current Set. A resistor connected between PEAKSET and ground (RPEAKSET) programs the
peaking current amplitude. To disable peaking, leave PEAKSET open.
Transmit Disable. Driver output is disabled when TX_DISABLE is high or left unconnected. The driver
output is enabled when the pin is asserted low.
8, 16
GND
Ground
10
OUT-
Inverted Modulation-Current Output
11
OUT+
Noninverted Modulation-Current Output
12
BIASMON
13
BIAS
14
BIASSET
Bias Current Set. A resistor connected between BIASSET and ground (RBIASSET) programs the
VCSEL bias current.
EP
Exposed
Pad
Ground. This must be soldered to the circuit board ground for proper thermal and electrical
performance. See the Layout Considerations section.
Bias Current Monitor. The output of BIASMON is a sourced current proportional to the bias current. A
resistor connected between BIASMON and ground (RBIASMON) can be used to form a ground
referenced bias monitor.
Bias Current Output
_______________________________________________________________________________________
5
MAX3741
Typical Operating Characteristics (continued)
(VCC = +3.3V, TA = 25°C, measured electrically with a 50Ω load AC-coupled to OUT+, unless otherwise noted.)
MAX3741
3.2Gbps Compact SFP VCSEL Driver
Functional Diagram
BIASSET
ENABLE
TX_DISABLE
BIASMON
BIAS
GENERATOR
VCC
BIAS
ROUT
OUTOUT+
IN+
PEAKING
CONTROL
100Ω
INENABLE
MODULATION-CURRENT
GENERATOR
MODSET
Applications Information
VCSEL Selection
LASER
MODULATOR
MAX3741
ROUT
Input Termination
The MAX3741 data inputs are SFP MSA compatible.
On-chip 100Ω differential input impedance is provided
for optimal termination (Figure 4). The MAX3741 inputs
self-bias to the proper operating point to accommodate
AC-coupling.
PEAKSET
Select a communications-grade VCSEL with a rise time
of 260ps or better for 1.25Gbps or 130ps or better for
2.5Gbps applications.
Use a high-efficiency VCSEL that requires low modulation current and generates a low voltage swing. Trim the
leads to reduce VCSEL package inductance. The typical
package leads have inductance of 25nH per inch
(1nH/mm). This inductance causes a large voltage swing
across the VCSEL. A compensation filter network can be
used to reduce ringing, edge speed, and voltage swing.
See the Designing the Laser-Compensation Filter
Network section for more information.
Layout Considerations
Detailed Description
The MAX3741 contains a bias generator and a laser
modulator with optional peaking compensation.
To minimize inductance, keep the connections between
the MAX3741 output pins and VCSEL as close as possible. Use good high-frequency layout techniques and
multiple-layer boards with uninterrupted ground planes
to minimize EMI and crosstalk.
Bias Generator
Figure 1 shows the bias generator circuitry that contains a bandgap voltage reference, current mirror, and
bias monitor. The bias current output to the laser is
controlled with the RBIASSET resistor. For appropriate
RBIASSET values, see the Bias Current vs. RBIASSET
graph in the Typical Operating Characteristics.
The BIASMON output provides a current proportional to
the laser bias current given by:
IBIASMON = IBIAS / 9
Modulation Circuit
The modulation circuitry consists of an input buffer, a current mirror, and a high-speed current switch (Figure 2).
The modulators drive up to 15mA of modulation into a
50Ω VCSEL load.
CURRENT
AMPLIFIER
MAX3741
ENABLE
IBIAS
40
BIAS
BIASMON
IBIAS
9
0.8V
200Ω
RBIASMON
BIAS GENERATOR
BIASSET
The amplitude of the modulation current is set with resistor at MODSET (RMODSET). For appropriate RMODSET
values, see the IMOD vs. RMODSET graph in the Typical
Operating Characteristics. Figure 3 shows a simplified
diagram of the MAX3741 output stage.
RBIASSET
Figure 1. Bias Generator
6
_______________________________________________________________________________________
FERRITE
BEAD
3.2Gbps Compact SFP VCSEL Driver
MAX3741
ROUT
INPUT
BUFFER
IN+
ROUT
OUT+
OUT-
CURRENT
SWITCH
PEAKING
CONTROL
100Ω
PEAKSET
INMODULATION
CURRENT
GENERATION
CURRENT AMPLIFIER
34x
RPEAKSET
VCSEL package inductance causes the VCSEL impedance to increase at high frequencies, leading to ringing, overshoot, and degradation of the VCSEL output. A
VCSEL compensation filter network can be used to
reduce the VCSEL impedance at high frequencies,
thereby reducing output ringing and overshoot.
The compensation components (RF and CF) are most
easily determined by experimentation. Begin with RF =
50Ω and CF = 1pF. Increase CF until the desired transmitter response is obtained (Figure 5). Refer to
Application Note HFAN-2.0: Interfacing Maxim Laser
Drivers with Laser Diodes for more information.
ENABLE
Exposed-Pad (EP) Package
The exposed pad on the 16-pin thin QFN provides a
very low thermal resistance path for heat removal from
the IC. The pad is electrical ground on the MAX3741
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 Pad
Packages, for additional information.
1.0V
MODSET
RMODSET
Figure 2. Modulation Circuit
VCC
MAX3741
ROUT
VCC
PACKAGE
ROUT
1nH
16kΩ
OUTPACKAGE
VCC
0.5pF
IN+
1nH
OUT+
1nH
0.5pF
50Ω
0.5pF
VCC
50Ω
IN-
1nH
0.5pF
MAX3741
Figure 3. Simplified Output Structure
24kΩ
Figure 4. Simplified Input Structure
_______________________________________________________________________________________
7
MAX3741
Designing the Compensation
Filter Network
VCC
Laser Safety and IEC 825
The International Electrotechnical Commission (IEC)
determines standards for hazardous light emissions
from fiber-optic transmitters. IEC 825 defines the maximum light output for various hazard levels. Using this
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.
Customers must determine the level of fault tolerance
required by their applications, recognizing that Maxim
products are not designed or 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 where the failure of a Maxim product could create a situation where
personal injury or death may occur.
UNCOMPENSATED
CORRECTLY COMPENSATED
POWER
MAX3741
3.2Gbps Compact SFP VCSEL Driver
OVERCOMPENSATED
TIME
Figure 5. Laser Compensation
Chip Information
TRANSISTOR COUNT: 1597
PROCESS: SiGe bipolar
8
_______________________________________________________________________________________
3.2Gbps Compact SFP VCSEL Driver
12x16L QFN THIN.EPS
D2
0.10 M C A B
b
D
D2/2
D/2
E/2
E2/2
CL
(NE - 1) X e
E
E2
L
e
CL
k
(ND - 1) X e
CL
0.10 C
CL
0.08 C
A
A2
A1
L
L
e
e
PACKAGE OUTLINE
12, 16L, THIN QFN, 3x3x0.8mm
21-0136
E
1
2
_______________________________________________________________________________________
9
MAX3741
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.)
MAX3741
3.2Gbps Compact SFP VCSEL Driver
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.)
EXPOSED PAD VARIATIONS
DOWN
BONDS
ALLOWED
NOTES:
1. DIMENSIONING & TOLERANCING CONFORM TO ASME Y14.5M-1994.
2. ALL DIMENSIONS ARE IN MILLIMETERS. ANGLES ARE IN DEGREES.
3. N IS THE TOTAL NUMBER OF TERMINALS.
4. THE TERMINAL #1 IDENTIFIER AND TERMINAL NUMBERING CONVENTION SHALL CONFORM TO
JESD 95-1 SPP-012. DETAILS OF TERMINAL #1 IDENTIFIER ARE OPTIONAL, BUT MUST BE LOCATED
WITHIN THE ZONE INDICATED. THE TERMINAL #1 IDENTIFIER MAY BE EITHER A MOLD OR
MARKED FEATURE.
5. DIMENSION b APPLIES TO METALLIZED TERMINAL AND IS MEASURED BETWEEN 0.20 mm AND 0.25 mm
FROM TERMINAL TIP.
6. ND AND NE REFER TO THE NUMBER OF TERMINALS ON EACH D AND E SIDE RESPECTIVELY.
7. DEPOPULATION IS POSSIBLE IN A SYMMETRICAL FASHION.
8. COPLANARITY APPLIES TO THE EXPOSED HEAT SINK SLUG AS WELL AS THE TERMINALS.
9. DRAWING CONFORMS TO JEDEC MO220 REVISION C.
PACKAGE OUTLINE
12, 16L, THIN QFN, 3x3x0.8mm
21-0136
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.
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Printed USA
is a registered trademark of Maxim Integrated Products.