SY84782UMGTR [MICREL]
Low Power 2.5V 1.25Gbps FP/DFB Laser Diode Driver; 低功耗2.5V的1.25Gbps FP / DFB激光二极管驱动器
| 型号： | SY84782UMGTR |
| 厂家： | 
MICREL SEMICONDUCTOR |
| 描述： | Low Power 2.5V 1.25Gbps FP/DFB Laser Diode Driver |
| 文件： | 总9页 (文件大小：295K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
SY84782U
Low Power 2.5V 1.25Gbps FP/DFB Laser
Diode Driver
General Description
Features
The SY84782U is a single 2.5V supply, ultra-low power,
small form factor laser diode driver for telecom/datacom
applications. Intended to drive FP/DFB lasers at data rates
up to 1.25Gbps, it is especially useful for Compact SFP,
SFP and SFF modules where power requirements are
quite stringent. The driver can deliver modulation current
up to 90mA and offers a high compliance voltage, all of
which make the SY84782U suitable for high current
operations in both AC and DC coupled applications.
• 2.5V power supply option
• Ultra low power consumption (63mW typ)
• Multirate up to 1.25Gbps
• Fast rise and fall time
• Modulation current up to 90mA
• Laser may be DC or AC coupled
• Guaranteed operation over –40°C to +85°C
The SY84782U is intended to be used with Micrel’s
MIC3003 Optical Transceiver Management IC, which
allows for both modulation and bias current control and
monitoring. Furthermore, the MIC3003 offers power control
and temperature compensation.
temperature range
• Small form factor 16-pin (3mm x 3mm) QFN package
• MIC3003G Compatible
Applications
This device operates across the industrial temperature
range (–40°C to +85°C) and is available in a small 3mm x
3mm QFN package.
• Multirate LAN, MAN applications: Fibre Channel, GbE,
SONET OC3/12/24 and SDH STM1/4/8
All datasheets and support documentation can be found
on Micrel’s web site at: www.micrel.com.
• CSFP/SFF/SFP Optical Modules
___________________________________________________________________________________________________________
Typical Application
AC-coupled Laser
DC-coupled Laser
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
M9999-012411-A
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SY84782U
Functional Block Diagram
Ordering Information
Part Number
Package
Type
Operating
Range
Package Marking
Lead
Finish
SY84782UMG
QFN-16
Industrial
782U
Pb-Free
Pb-Free
Pb-Free bar-line indicator
SY84782UMG TR(1)
QFN-16
Industrial
782U
Pb-Free bar-line indicator
Note:
1. Tape and Reel
Pin Configuration
16-Pin QFN
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Pin Description
Pin Number
Pin Name
GND,
Pin Function
1, 4, 7, 8, 13
Device Ground. Ground and exposed pad must be connected to the plane of the most
negative potential.
Exposed Pad
DIN+
2
3
Non-Inverting Input Data. Internally terminated with 50Ohm to a reference voltage
Inverting Input Data. Internally terminated with 50Ohm to a reference voltage
DIN-
5, 6
VCC
Supply Voltage. Bypass with a 0.1uF || 0.01uF low ESR capacitor as close to VCC pin as
possible.
9, 10
MOD-
MOD+
Inverted Modulation Current Output. Provides modulation current when input data is
negative
11, 12
Non-Inverted Modulation Current Output. Provides modulation current when input data is
positive.
14
15
VREF
Reference Voltage. Install a 0.1uF capacitor between VREF and VCC
IM_SET
Modulation current setting and control. The voltage applied to this pin will set the
modulation current. To be connected to the MIC3003 pin 24 (VMOD+). Input impedance
25KOhm.
16
/EN
Enable Pin. A high level signal applied to this pin will pull the MOD+ output HIGH and
MOD- output LOW. Internally pulled down with a 75KOhm resistor.
Truth Table
DIN+
DIN-
H
/EN
L
MOD+ (1)
MOD-
Laser Output (2)
L
H
X
H
L
L
H
L
L
H
L
L
L
X
H
H
Notes:
1. IMOD = 0 when MOD+ = H
2. Assuming that Laser is tied to MOD+
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SY84782U
Absolute Maximum Ratings(1)
Operating Ratings(2)
Supply Voltage (VCC) .................................. –0.5V to +3.0V
Input Voltage (VIN) .......................................... –0.5V to VCC
TTL Control Input Voltage (VIN) ........................... 0V to VCC
Supply Voltage (VCC) .............................. 2.375V to 2.625V
Ambient Temperature (TA) .........................–40°C to +85°C
Package Thermal Resistance(3)
Still-Air (θJA).......................................................60°C/W
Junction-to-Board (ΨJB).....................................33°C/W
Lead Temperature (soldering, 20 sec.)....................+260°C
Storage Temperature (TS) .......................–65°C to +150°C
DC Electrical Characteristics(4)
VCC = 2.5V ±5%, TA = –40°C to +85°C. Typical values are VCC = 2.5V, TA = 25°C, IMOD = 60mA
Symbol
Parameter
Condition
Min
Typ
Max
Units
ICC
Power Supply Current
Modulation current excluded
24
30(5)
mA
Minimum voltage required at
driver output for proper
operation
VMOD_MIN
0.6
45
V
RiIN(DATA)
RiIN(IMOD_SET)
VID
Input resistance (DIN+, DIN-)
Input resistance (IM_SET)
Differential Input Voltage Swing
/EN Input High
50
25
55
Ω
KΩ
mVpp
V
200
2
2400
VIH_EN
VIL_EN
/EN Input Low
0.8
1.2
V
VIM_SET
Voltage Range on IM_SET Pin
IMOD range 10mA – 90mA
V
AC Electrical Characteristics(4)
VCC = 2.5V ±5%, TA = –40°C to +85°C. Typical values are VCC = 2.5V, TA = 25°C, IMOD = 60mA
Symbol
Parameter
Condition
NRZ Data
Min
0.155
10
Typ
Max
1.25
90
Units
Gbps
mA
Data Rate
Modulation Current
(15Ω Load)
AC-Coupled
DC-Coupled
IMOD
10
70(6)
mA
Current at MOD+ when the device
is disabled
IMOD_OFF
Modulation OFF current
750
uA
Total Jitter
@ 1.25Gbps data rate
20
20
pspp
ps
Pulse-Width Distortion
IMOD range 10mA – 90mA
Output Rise/Fall Times
(20% to 80%)
tr, tf
15Ω Load
100
140
ps
Notes:
1. Exceeding the absolute maximum rating may damage the device.
2. The device is not guaranteed to function outside its operating rating.
3. Package Thermal Resistance assumes exposed pad is soldered (or equivalent) to the devices most negative potential on the PCB.
4. Specification for packaged product only.
5. Icc = 30mA (excluding IMOD) for worst case conditions with VCC = 2.625V, TA = 85°C, IMOD = 60mA
6. Assuming VCC = 2.375V, laser bandgap voltage = 1V, laser package inductance = 1nH, laser equivalent series resistor = 5Ω, and damping resistor =
10Ω.
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Micrel, Inc.
SY84782U
Typical Operating Characteristics
VCC = 2.5V ±5%, TA = –40°C to +85°C. Typical values are VCC = 2.5V, TA = 25°C, IMOD = 60mA
Supply Current vs IMOD
IM_SET vs Modulation Current
IMOD vs VMOD
(Compliance Voltage)
(IMOD Excluded)
100
90
80
70
60
50
40
30
20
10
0
30
25
20
15
10
100
90
80
70
60
50
40
30
20
10
0
0
200
400
600
800
1000
0
10 20 30 40 50 60 70 80 90 100
0
0.2
0.4
0.6
0.8
1
1.2
IM_SET Voltage (mV)
Modulation Current (mA)
VMOD (V)
Functional Characteristics
VCC = 2.5V ±5%, TA = –40°C to +85°C. Typical values are VCC = 2.5V, TA = 25°C, IMOD = 60mA
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Input and Output Stages
Figure 1a. Simplified Input Stage
Figure 1b. Simplified Output Stage
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SY84782U
the same circuit using Rd = 10ꢀ, RComp = 100ꢀ, and
CComp = 3pF. The compensation network may change
from one board to another and from one type of laser to
another. An additional compensation network (RC) can
be added at the laser cathode for further compensation
and eye smoothing.
Application Information
The typical applications diagram on the first page shows
how to connect the driver to the laser single-ended. To
improve transition time and laser response, the laser can
be driven differentially, as shown in Figures 2 and 3.
Driving the laser differentially will also minimize crosstalk
with the rest of the circuitry on the board, particularly the
receiver.
DC-Coupling
In addition to the low power consumption and high
modulation current, the SY84782U offers a high
compliance voltage. The minimum voltage needed at the
output of the driver for proper operation is less than
600mV, leaving a large headroom, VCC-600mV, to the
laser with the damping resistor. To show the importance
of this high compliance voltage, consider the voltage
drops along the path from VCC to ground through the
laser, damping resistor, and driver:
V
CC = Driver Headroom + VRd + Vlaser
Rd = Rd x IMOD
V
Vlaser = Vband-gap + Rlaser x IMOD + Ldi/dt
Figure 2. Laser DC-Coupled
AC-Coupling
Vband-gap + Rlaser x IMOD = 1.6V at maximum for a
Fabry Perrot or a DFB laser.
When trying to AC-couple the laser to the driver, the
headroom of the driver is no longer a problem since it is
DC isolated from the laser with the coupling capacitor. At
the output, the headroom of the driver is determined by
the pull-up network. In Figure 3, the modulation current
out of the driver is split between the pull-up network and
the laser. If, for example, the total pull-up resistor is
twice the sum of the damping resistor and laser
equivalent series resistance, then only two thirds (2/3) of
the modulation current will be used by the laser.
Therefore, to keep most of the modulation current going
through the laser, the total pull-up resistor must be kept
as high as possible. One solution involves using an
inductor alone as pull-up, presenting a high impedance
path for the modulation current and zero ohm (0ꢀ) path
for the DC current offering headroom of the driver equal
to VCC and almost all the modulation current goes into
the laser. The inductor alone will cause signal distortion,
and, to improve this phenomenon, a combination of
resistors and inductors can be used (as shown on Figure
3). In this case, the headroom of the driver is VCC-R1 x
αIMOD, where αIMOD is the portion of the modulation
current that goes through the pull-up network.
Ldi/dt is the voltage drop due to the laser parasitic
inductance during IMOD transitions. Assuming L = 1nH, tf
= tf = 80ps (measured between 20% and 80% of IMOD),
and IMOD = 70mA (42mA from 20% to 80%), then Ldi/dt
will be equal to 525mV. This number can be minimized
by making the laser leads as short as possible and by
using the RC compensation network between the
cathode of the laser and ground or across the laser
driver outputs, as shown in Figure 2.
To be able to drive the laser DC-coupled with a high
current, it is necessary to keep the damping resistor as
small as possible. For example, if the drop due to
parasitic inductance of the laser is neglected
(compensated for) and the maximum drop across the
laser (1.6V) considered while keeping a minimum of
600mV headroom for the driver, then the maximum
damping resistor that allows a 70mA modulation current
into the laser is:
R
dmax = (VCC-0.6V-1.6V)/0.07A
The worst case will be with VCC = 3.0V, leading
to Rdmax = 11.4ꢀ
On the other hand, the smaller the value of Rd, the
higher is the overshoot/undershoot on the optical signal
from the laser. In the circuit shown in Figure 3, the RC
compensation network across the driver outputs (MOD+
and MOD-) allows the user Rd = 10ꢀ. The optical eye
diagrams at data rates of 1.25Gbps, shown in
“Functional Characteristics” section, are all obtained with
When the laser is AC-coupled to the driver, the coupling
capacitor creates a low-frequency cutoff in the circuit,
and its value must be chosen to be as large as possible.
If the value of the cap is too high, it will slow down the
fast signals edges, and conversely, if its value is too
small, it won’t be able to hold a constant change
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Micrel, Inc.
SY84782U
between the first bit and the last bit of a long string of
identical bits in a low data rate application. This leads to
higher pattern-dependent jitter in the transmitter signal.
0.1µF is found to be good for all applications from
155Mbps to 1.25Gbps.
AC-coupling the laser to the driver brings a solution to
the driver headroom problem at the expense of extra
components, loss of part of the modulation current
wasted in the pull-up network, and additional power
consumption.
Figure 3. Laser AC-Coupled
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January 2011
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Micrel, Inc.
SY84782U
Package Information
16-Pin (3mm x 3mm) QFN® (QFN-16)
MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http://www.micrel.com
Micrel makes no representations or warranties with respect to the accuracy or completeness of the information furnished in this data sheet. This
information is not intended as a warranty and Micrel does not assume responsibility for its use. Micrel reserves the right to change circuitry,
specifications and descriptions at any time without notice. No license, whether express, implied, arising by estoppel or otherwise, to any intellectual
property rights is granted by this document. Except as provided in Micrel’s terms and conditions of sale for such products, Micrel assumes no liability
whatsoever, and Micrel disclaims any express or implied warranty relating to the sale and/or use of Micrel products including liability or warranties
relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right.
Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product
can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant
into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A
Purchaser’s use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully
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© 2011 Micrel, Incorporated.
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