XTEAWT-00-0000-000000FP0 - CREE

SY88982L

3.3V, 2.7Gbps High-Current, Low-Power

Laser Driver for FP/DFB Lasers

9-121009-A

cember 2009 M999

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General Description

The SY88982L is a single 3.3V supply, low power

consumption, small form factor driver for

telecom/datacom applications using FP/DFB lasers

at data rates up to 2.7Gbps. The driver can deliver

modulation current up to 90mA, and the high

compliance voltage if offers, makes the part suitable

for high-current operation (with the laser AC- or DC-

coupled to it). This device is intended to be used

with Micrel’s MIC3003 Optical Transceiver

Management IC, which allows for both modulation

and bias current control and monitoring, automatic

power control, and temperature compensation.

All support documentation can be found on Micrel’s

web site at: www.micrel.com.

Features

• 2.4V minimum laser compliance voltage for high-

current DC-coupled applications

• 48mA power supply current typical

• Operation up to 2.7Gbps

• Modulation current up to 90mA

• Designed for use with the MIC3003

• Laser may be DC- or AC-coupled

• Small form factor 16-pin (3mm x 3mm) MLF™

package

Applications

• Multi-rate LAN, MAN applications up to 2.7Gbps:

FC, GbE, SONET OC3/12/24/48 and SDH

STM1/4/8/16

• SFF, SFP modules

Markets

• Telecom, Datacom

________________________________________________________________

Typical Application

Laser DC-Coupled to the Driver

Laser AC-Coupled to the Driver

8) 955-1690

Micrel, Inc. SY88982L

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Functional Block Diagram

Ordering Information(1)

Part Number Package Type Operating Range Package Marking Lead Finish

SY88982LMG MLF-16 Industrial 982L with Pb-Free bar-line indicator NiPdAu Pb-Free

SY88982LMGTR(2) MLF-16 Industrial 982L with Pb-Free bar-line indicator NiPdAu Pb-Free

Notes:

1. Contact factory for die availability. Dice are guaranteed at TA = +25°C, DC Electricals only.

2. Tape and Reel.

Pin Configur ation

16-Pin MLFTM (MLF-16)

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Pin Description

Pin Number Pin Name Pin Function

1, 4, 7, 8, 13 GND Ground. Ground and exposed pad must be connected to the plane of the most negative

potential.

2 DIN+

Non-Inverting Input Data. Internally terminated with 50Ω to a reference voltage.

3 DIN-

Inverting Input Data. Internally terminated with 50Ω to a reference voltage.

5, 6 VCC Supply Voltage. Bypass with a 0.1µF//0.01µF low ESR capacitor as close to VCC pin as

possible.

9, 10 MOD- Inverted Modulation Current Output. Provides modulation current when input data is

negative.

11, 12 MOD+ Non-Inverted Modulation Current Output. Provides modulation current when input data is

positive.

14 VREF Reference Voltage. Install a 0.1µF capacitor between VREF and VCC.

15 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 25k.

16 /EN

A high level signal applied to this pin will disable the output stage of the driver. Internally

pulled down with 25kΩ resistor.

Truth Table

DIN+ DIN- /EN MOD+(1) MOD- Laser Output(2)

L H L H L L

H L L L H H

X X H H H L

Notes:

1. IMOD = 0 when MOD+ = H.

2. Assuming that the laser is tied to MOD+.

Micrel, Inc. SY88982L

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Absolute Maximum Ratings(1)

Supply Voltage (VIN) ...........................–0.5V to +4.0V

CML Input Voltage (VIN).......... VCC–1.2V to VCC+0.5V

TTL Control Input Voltage (VIN) ...................0V to VCC

Lead Temperature (soldering, 20sec.) ...........+260°C

Storage Temperature (Ts)............... –65°C to +150°C

Operating Ratings(2)

Supply Voltage (VCC)...........................+3.0V to +3.6V

Ambient Temperature (TA)................ –40°C to +85°C

Package Thermal Resistance(3)

MLF™

(θJA) Still-air ............................................. 60°C/W

(ψJB) ......................................................... 33°C/W

DC Electrical Characteristics

TA = -40°C to 85°C and VCC = +3.0V to +3.6V, unless otherwise noted. Typical values are VCC = +3.3V, TA = 25°C,

IMOD = 60mA.

Symbol Parameter Condition Min Typ Max Units

ICC Power Supply Current Modulation current excluded 48 65(4) mA

VMOD_MIN

Minimum Voltage Required at

the Driver Output (headroom) for

Proper Operation

0.6 V

RIN(DATA) Input Resistance (DIN+, DIN-) 45 50 55 

VID Differential Input Voltage Swing 200 2400 mVPP

/EN Low 0.8 V

/EN High 2 V

RIN (IMOD_SET) I

M_SET Input Resistance 25 k

VIM_SET Voltage Range on IM_SET Pin IMOD range 10mA – 90mA 1.2 V

AC Electrical Characteristics

TA = -40°C to 85°C and VCC = +3.0V to +3.6V, unless otherwise noted. Typical values are VCC = +3.3V, TA = 25°C,

IMOD = 60mA.

Symbol Parameter Condition Min Typ Max Units

Data Rate NRZ 0.155 2.7 Gbps

IMOD Modulation Current(5) AC-coupled 10 90 mA

DC-coupled 10 70(6) mA

IMOD_OFF Modulation OFF Current Current at MOD+ when the device is

disabled. 750 µA

tr Output Current Rise Time 20% to 80%, IMOD = 60mA, 15 load 55 80 ps

tf Output Current Fall Time 20% to 80%, IMOD = 60mA, 15 load 55 80 ps

Total Jitter @2.5Gbps data rate 20 psPP

Pulse-Width Distortion IMOD range 10mA – 90mA 20 ps

Notes:

1. Permanent device damage may occur if absolute maximum ratings are exceeded. This is a stress rating only and functional operation is

not implied at conditions other than those detailed in the operational sections of this data sheet. Exposure to absolute maximum ratings

conditions for extended periods may affect device reliability.

2. The data sheet limits are not guaranteed if the device is operated beyond the operating ratings.

3. Package Thermal Resistance assumes exposed pad is soldered (or equivalent) to the devices most negative potential on the PCB. ψJB

uses a 4-layer and θJA in still air unless otherwise stated.

4. ICC = 48mA for worst-case conditions with IMOD = 90mA, TA = +85°C, VCC = 3.6.

5. Load = 15.

6. Assuming VCC = 3.0V, Laser bandgap voltage = 1V, laser package inductance = 1nH, laser equivalent series resistor = 5, and damping

resistor = 10.

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Typical Operating Characteristics

Test Circuit

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Functional Characteristics

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Input and Output Stages

Figure 1a. Simplified Input Stage

Figure 1b. Simplified Output Stage

Interfacing the Input to Different Logic Drivers

Figure 2a. DC-Coupling to LVPECL Driver

Figure 2b. AC-Coupling to LVPECL Driver

Figure 2c. AC-Coupling to CML Driver

Figure 2d. AC-Coupling to LVDS Driver

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Micrel, Inc. SY88982AL

December 2009

M9999-121009-A

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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 3 and 4. Driving the laser

differentially will also minimize the crosstalk with the

rest of the circuitry on the board, especially the

receiver.

DC-Coupling

In addition to the low power consumption and high

modulation current, the SY88982L offers a high

compliance voltage. As can be seen in the “Typical

Operating Characteristics” section (IMOD vs. VMOD

curves), 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:

or (408) 955-1690

VCC = Driver Headroom + VRd + Vlaser

VRd = Rd x IMOD

Vlaser = Vband-gap + Rlaser x IMOD + Ldi/dt

Vband-gap + Rlaser x IMOD = 1.6V at maximum for

a Fabry Perrot or a DFB laser.

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 using and RC compensation network

between the cathode of the laser and ground or

across the laser driver outputs as shown in Figure 3.

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:

Rdmax = (VCC-0.6V-1.6V)/0.07A

The worst case will be with VCC = 3.0V,

leading to Rdmax = 11.4

On the other hand, the small is 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 =

10. The optical eye diagrams at data rates of

155Mbps/622Mbps/1.25Gbps/2.5Gbps, shown in

“Functional Characteristics” section, are all obtained

with the same circuit using Rd = 10, RComp = 100,

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.

Figure 3. Laser DC-Coupled

AC-Coupling

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 4, 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, only

two thirds (2/3) of the modulation current will be

used by the laser. So, 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 consists in using an inductor alone as

pull-up, presenting a high impedance path for the

modulation current and zero ohm (0) path for the

DC current offering a 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 that, a combination of

resistors and inductors can be used (as shown on

Figure 4). 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

Micrel, Inc. SY88982L

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network.

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 as large as

possible. If the value of the cap is too high, it will

slow down the fast signals edges, and, if its value is

too small, it won’t be able to hold a constant change

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 2.7Gbps.

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 4. Laser AC-Coupled

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Package Information

16-Pin (3mm x 3mm) MLF™ (MLF-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

The information furnished by Micrel in this data sheet is believed to be accurate and reliable. However, no responsibility is assumed by Micrel

for its use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer.

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 indemnify Micrel for any damages resulting from such use or sale.

Incor

orated.

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