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, • 2.5V power supply option small form factor laser diode driver for telecom/datacom applications. Intended to drive FP/DFB lasers at data rates • Ultra low power consumption (63mW typ) up to 1.25Gbps, it is especially useful for Compact SFP, • Multirate up to 1.25Gbps SFP and SFF modules where power requirements are • Fast rise and fall time quite stringent. The driver can deliver modulation current • Modulation current up to 90mA up to 90mA and offers a high compliance voltage, all of which make the SY84782U suitable for high current • Laser may be DC or AC coupled operations in both AC and DC coupled applications. • Guaranteed operation over –40°C to +85°C The SY84782U is intended to be used with Micrel’s temperature range MIC3003 Optical Transceiver Management IC, which • Small form factor 16-pin (3mm x 3mm) QFN package allows for both modulation and bias current control and • MIC3003G Compatible monitoring. Furthermore, the MIC3003 offers power control and temperature compensation. Applications This device operates across the industrial temperature range (–40°C to +85°C) and is available in a small 3mm x • Multirate LAN, MAN applications: Fibre Channel, GbE, 3mm QFN package. SONET OC3/12/24 and SDH STM1/4/8 All datasheets and support documentation can be found • CSFP/SFF/SFP Optical Modules on Micrel’s web site at: www.micrel.com. ___________________________________________________________________________________________________________ Typical Application DC-coupled Laser AC-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 January 2011 M9999-012411-A [email protected] or (408) 955-1690 Micrel, Inc. SY84782U Functional Block Diagram Ordering Information Part Number Package Type Operating Range Package Marking Lead Finish SY84782UMG QFN-16 Industrial 782U Pb-Free bar-line indicator Pb-Free SY84782UMG TR(1) QFN-16 Industrial 782U Pb-Free bar-line indicator Pb-Free Note: 1. Tape and Reel Pin Configuration 16-Pin QFN January 2011 2 M9999-012411-A [email protected] or (408) 955-1690 Micrel, Inc. SY84782U Pin Description Pin Number Pin Name 1, 4, 7, 8, 13 GND, Exposed Pad Pin Function Device 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 50Ohm to a reference voltage 3 DIN- Inverting Input Data. Internally terminated with 50Ohm to a reference voltage 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- 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 0.1uF capacitor between VREF and VCC 15 IM_SET 16 /EN 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. 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- /EN MOD+ (1) MOD- Laser Output (2) L H L H L L H L L L H H X X H H L L Notes: 1. IMOD = 0 when MOD+ = H 2. Assuming that Laser is tied to MOD+ January 2011 3 M9999-012411-A [email protected] or (408) 955-1690 Micrel, Inc. 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 Lead Temperature (soldering, 20 sec.).................... +260°C Storage Temperature (TS) .......................–65°C to +150°C 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 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 ICC Power Supply Current VMOD_MIN Minimum voltage required at driver output for proper operation 0.6 RiIN(DATA) Input resistance (DIN+, DIN-) 45 RiIN(IMOD_SET) Input resistance (IM_SET) VID Differential Input Voltage Swing VIH_EN /EN Input High VIL_EN /EN Input Low VIM_SET Voltage Range on IM_SET Pin Typ Modulation current excluded 24 Max 30 (5) Units mA V 50 55 25 200 Ω KΩ 2400 2 mVpp V IMOD range 10mA – 90mA 0.8 V 1.2 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 IMOD IMOD_OFF tr, tf Parameter Condition Min Max Units Data Rate NRZ Data 0.155 Typ 1.25 Gbps Modulation Current AC-Coupled 10 90 mA (6) mA (15Ω Load) DC-Coupled Modulation OFF current Current at MOD+ when the device is disabled 750 uA Total Jitter @ 1.25Gbps data rate 20 pspp Pulse-Width Distortion IMOD range 10mA – 90mA 20 ps Output Rise/Fall Times (20% to 80%) 15Ω Load 140 ps 10 70 100 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. January 2011 4 M9999-012411-A [email protected] or (408) 955-1690 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 (IMOD Excluded) IM_SET vs Modulation Current 100 30 100 90 90 70 60 50 40 30 20 80 25 70 IMOD (mA) Supply Current (mA) 80 IMOD (mA) IMOD vs VMOD (Compliance Voltage) 20 60 50 40 30 15 20 10 10 0 10 0 200 400 600 800 1000 IM_SET Voltage (mV) 0 0 10 20 30 40 50 60 70 80 90 100 0 Modulation Current (mA) 0.2 0.4 0.6 0.8 1 1.2 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 January 2011 5 M9999-012411-A [email protected] or (408) 955-1690 Micrel, Inc. SY84782U Input and Output Stages Figure 1a. Simplified Input Stage January 2011 Figure 1b. Simplified Output Stage 6 M9999-012411-A [email protected] or (408) 955-1690 Micrel, Inc. SY84782U the same circuit using Rd = 10Ω, RComp = 100Ω, 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: 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 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: Rdmax = (VCC-0.6V-1.6V)/0.07A The worst case will be with VCC = 3.0V, leading to Rdmax = 11.4Ω 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 = 10Ω. The optical eye diagrams at data rates of 1.25Gbps, shown in “Functional Characteristics” section, are all obtained with January 2011 Figure 2. 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 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 (0Ω) 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. 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 7 M9999-012411-A [email protected] or (408) 955-1690 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 January 2011 8 M9999-012411-A [email protected] or (408) 955-1690 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 indemnify Micrel for any damages resulting from such use or sale. © 2011 Micrel, Incorporated. January 2011 9 M9999-012411-A [email protected] or (408) 955-1690