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3-channel laser diode driver with oscillator ad9662 rev. c information furnished by analog devices is believed to be accurate and reliable. however, no responsibility is assumed by analog devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. specifications subject to change without notice. no license is granted by implication or otherwise under any patent or patent rights of analog devices. trademarks and registered trademarks are the property of their respective owners. one technology way, p.o. box 9106, norwood, ma 02062-9106, u.s.a. tel: 781.329.4700 www.analog.com fax: 781.461.3113 ? 2005 analog devices, inc. all rights reserved. features current-controlled current source with 3 input channels output current for channel 3315 ma output current for other channels210 ma rise time/fall time of 0.8 ns on-chip oscillator single 5 v power supply (10%) low output overshoot low power consumption applications cd-rw drives dvd-rw, dvd+rw, mo drives laser diode current switching general description the ad9662 is a laser diode driver for high performance cd and dvd recordable drives. it includes three channels for three different optical power levels: the read channel generates a continuous output power level, whereas channel 2 and channel 3 are used as write channels having 0.8 ns rise/fall times. all channel currents are summed at the i out pin. each channels output current is established by multiplying the channels gain by the channels input current. the input current for each of the input channelsinr, in2, and in3can be set either by using an external resistor that converts an input voltage to a current or by directly using a current source. an on-chip oscillator is provided to allow output current modulation (to reduce laser mode hopping). two external resistors control the frequency and the amplitude swing of the oscillator. the push-pull oscillator can swing up to 100 ma p-p and has a frequency range of 200 mhz to 500 mhz. functional block diagram channel 3 channel 2 read channel oscillator output i out enable r s r f 04389-0-001 in3 outen3 in2 outen2 inr outenr oscen figure 1. ad9662 3-channel laser diode driver
ad9662 rev. c | page 2 of 16 table of contents features .............................................................................................. 1 applications ....................................................................................... 1 general description ......................................................................... 1 functional block diagram .............................................................. 1 revision history ............................................................................... 2 specifications ..................................................................................... 3 absolute maximum ratings ............................................................ 5 esd caution .................................................................................. 5 pin configuration and function descriptions ..............................6 typical performance characteristics ..............................................7 applications ..................................................................................... 10 temperature considerations .................................................... 10 evaluation board ............................................................................ 12 outline dimensions ....................................................................... 13 ordering guide .......................................................................... 13 revision history 11/05rev. spb to rev. c changes to format .............................................................universal 7/04rev. sp0 to rev. spb changes to note 2 in specifications............................................... 4 changes to absolute maximum ratings ....................................... 5 changes to figure 17...................................................................... 12 12/03rev. spa: initial 2-page web version 12/03rev. sp0: initial full version
ad9662 rev. c | page 3 of 16 specifications at t amb , v cc = 5 v, enable = 1, oscen = 0, outenx = 1, unless otherwise stated. table 1. parameter conditions min typ max unit laser amplifier output current read channel output is sourcing, outenr = 0 210 235 ma output current channel 2 output is sourcing, outen2 = 0 210 235 ma output current channel 3 output is sourcing, outen3 = 0 315 340 ma total output current output is sourcing, outen3 = 0 and ( outenr = 0 and/or outen2 = 0) >550 ma output current linearity 1 read channel, outenr = 0 ?4 0.6 +4 % output current linearity 1 write2 channel, outen2 = 0 ?4 0.6 +4 % output current linearity 1 write3 channel, outen3 = 0 ?4 0.1 +4 % best-fit current gain 1 read channel, outenr = 0 125 135 145 ma/ma best-fit current gain 1 write2 channel, outen2 = 0 120 130 140 ma/ma best-fit current gain 1 write3 channel, outen3 = 0 240 260 280 ma/ma best-fit current offset 1 read channel, outenr = 0 ?7 0.6 +7 ma best-fit current offset 1 write2 channel, outen2 = 0 ?7 0.6 +7 ma best-fit current offset 1 write3 channel, outen3 = 0 ?30 ?2 +15 ma i out series resistance total r out to v cc rail 6.5 10 input impedance (r in ), channel r, channel 2 r in to gnd 160 200 240 input impedance (r in ), channel 3 r in to gnd 80 100 120 i out supply sensitivity (psrr) i out = 50 ma (read-only), v cc = 5 v 10% 10 15 %/v read mode outenr = 0 i out supply sensitivity (psrr) i out = 100 ma (50 ma read, 50 ma write) 10 15 %/v write mode v cc = 5 v 10%, outenr = 0 and ( outen2 = 0 or outen3 = 0) output current noise i out = 50 ma (read), outenr = 0, f = 300 mhz 150 pa/hz i out temperature sensitivity i out = 50 ma (read-only) 100 ppm/c read mode outenr = 0 i out temperature sensitivity i out = 100 ma (50 ma read, 50 ma write2) 100 ppm/c write mode channel 2 outenr = 0, outen2 = 0 i out temperature sensitivity i out = 100 ma (50 ma read, 50 ma write3) 100 ppm/c write mode channel 3 outenr = 0, outen3 = 0 laser amplifier ac specifications write rise time 2 i out = 50 ma dc (read), 50 ma pulse w2 or w3 0.8 1.8 ns outenr = 0 and ( outen2 = 0 or outen3 = 0) write fall time 2 i out = 50 ma dc (read), 50 ma pulse w2 or w3 0.6 1.8 ns outenr = 0 output current overshoot i out = 50 ma dc (read), 50 ma pulse w2 or w3 13 % outenr = 0 and ( outen2 = 0 or outen3 = 0) i out on propagation delay outenx 50% h-l to i out at 50% of final value 2.7 ns i out off propagation delay outenx 50% l-h to i out at 50% of initial value 2.7 ns disable time enable 50% h-l to i out at 50% of initial value 5.4 ns enable time enable 50% l-h to i out at 50% of final value 13.5 ns oscillator specifications outenr = 0 oscillator frequency r f = 9.53 k, r s = 23.7 k 265 300 325 mhz oscillator frequency temperature coefficient r f = 9.53 k, r s = 23.7 k 600 ppm/c disable time oscillator oscen 50% h-l to amplitude at 50% of initial value 4 ns enable time oscillator oscen 50% l-h to amplitude at 50% of final value 6 ns
ad9662 rev. c | page 4 of 16 parameter conditions min typ max unit logic specifications logic hi threshold 2.0 v logic lo threshold 0.8 v input impedance outenx , enable, oscen >10 m input leakage current outenx , enable, oscen <1 a supply current enable oscen outenr outen2 outen3 power-down 0 0 1 1 1 8.5 10 ma power-up inputs disabled 1 0 1 1 1 18 22 ma inputs disabled, osc enabled 1 1 1 1 1 52 62 ma read mode, osc enabled 3 1 1 0 1 1 55 65 ma i out = 50 ma write mode 3 1 0 1 0 0 29 35 ma i out = 100 ma (50 ma w2, 50 ma w3) operating conditions supply voltage range 4.5 5.5 v operating temperature range 0 85 c 1 output linearity, offset current, and gain are calculated using a best-fit method at 30 ma, 45 ma, 60 ma, 75 ma, and 90 ma for the read and write2 channels and 90 ma, 105 ma, 120 ma, 135 ma, and 150 ma for write channe l 3. each channels outp ut current is given by i out = (i in gain) + i os . 2 this parameter is guaranteed by design and characterization using six sigma. rise an d fall times are measured electrically fro m the 10% to 90% points using a sharp gh0781ja2c diode as a load. 3 the values specified do not include the output current.
ad9662 rev. c | page 5 of 16 absolute maximum ratings table 2. parameter range supply voltage +v s pin 9, pin 15, and pin 16 5.5 v input pins pin 1 and pin 2 2.2 ma pin 5 1.6 ma pin 6, pin 7, pin 8, pin 10, and pin 11 ?0.8 v to +5.5 v internal power dissipation 1 16-lead qsop 620 mw operating temperature range 0c to +85c storage temperature range ?65c to +150c lead temperature, soldering 60 sec 300c 1 power dissipation is specified on semi standard 4-layer board. stresses above those listed under absolute maximum ratings may cause permanent damage to the device. this is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. esd caution esd (electrostatic discharge) sensitive device. electrosta tic charges as high as 4000 v readily accumulate on the human body and test equipment and can discharge without detection. although this product features proprietary esd protection circuitry, permanent dama ge may occur on devices subjected to high energy electrostatic discharges. therefore, proper esd pr ecautions are recommended to avoid performance degradation or loss of functionality.
ad9662 rev. c | page 6 of 16 pin configuration and fu nction descriptions ad9662 inr 1 in2 2 gnd 3 r f 4 v cc v cc i out gnd 16 15 14 13 04389-0-002 in3 5 outenr 6 outen2 7 outen3 8 r s enable oscen v cc 12 11 10 9 figure 2. pin configuration table 3. pin function descriptions pin no. nemonic description 1 inr input current pin for the read channel. has a typical input impedance of 200 . 2 in2 input current pin for write channel 2. has a typical input impedance of 200 . 3, 13 gnd common external ground reference. 4 r f pin used to set oscillator frequency by connecting a resistor from this pin to ground. 5 in3 input current pin for write channel 3. has a typical input impedance of 100 . 6 outenr ttl-compatible enable for the read channel. logic low active. 7 outen2 ttl-compatible enable for write channel 2. logic low active. 8 outen3 ttl-compatible enable for write channel 3. logic low active. 9, 15, 16 v cc power supply pins for the ad9662. each pin needs to be decoupled with a 0.1 f capacitor to ground. 10 oscen ttl-compatible enable for the oscillator. logic high active. 11 enable ttl-compatible enable for the device. logic high active. 12 r s pin used to set oscillator amplitude by connecting a resistor from this pin to ground. 14 i out output current pin. this pin is connect ed to the anode of a laser diode.
ad9662 rev. c | page 7 of 16 typical performance characteristics r s = 23.7 k, r f = 9.53 k, and read channel output current is 50 ma, unless otherwise noted. 04389-0-003 r f resistance (k ) oscillator frequency (mhz) 0 0 200 400 15 20 100 300 500 10 5 figure 3. oscillat or frequency vs. r f 04389-0-004 frequency (mhz) oscillator amplitude (ma p-p) 200 0 30 50 70 400 500 20 40 60 300 10 figure 4. oscillator amplitude vs. frequency 04389-0-005 frequency (mhz) current noise (na/ hz) 0.1 0.00 0.60 1.00 1.40 1000 0.40 0.80 1.20 100 1 0.20 10 figure 5. i out current noise r s resistance (k ) oscillator amplitude (ma p-p) 0 0 140 160 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 100 120 60 80 20 40 04389-0-006 figure 6. oscillat or amplitude vs. r s 04389-0-007 oscillator amplitude (ma p-p) supply current (ma) 0 60 110 130 130 150 100 120 120 100 70 110 80 90 10 140 20 30 40 50 60 70 80 90 figure 7. supply current vs. oscillator amplitude ?80 ?70 ?60 ?50 ?40 ?30 ?20 04389-0-008 oscillator frequency (mhz) distortion (dbc) 200 250 300 350 400 450 500 third harmonic second harmonic fourth harmonic fifth harmonic figure 8. oscillator harmonic distortion vs. frequency
ad9662 rev. c | page 8 of 16 04389-0-009 temperature (c) oscillator amplitude (ma p-p) ?40 35 55 20 60 100 40 ?20 40 80 0 45 50 figure 9. oscillator amplitude vs. temperature 04389-0-010 w 10ns/div figure 10. optical response 50 ma read, 50 ma write2, sharp gh0781ja2c diode i out (ma) 0 25 50 75 100 125 150 175 200 225 04389-0-011 0.50 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 (v cc ? v (i out )) (volts) figure 11. output current vs. voltage compliance 04389-0-012 temperature (c) oscillator frequency (mhz) ?40 275 280 295 305 20 60 100 290 300 ?20 40 80 0 285 figure 12. oscillator fr equency vs. temperature 04389-0-013 w 10ns/div figure 13. optical response 50 ma read, 200 ma write3, sharp gh0781ja2c diode write pulse zero level outen3 outen2 outenr 04389-0-017 t bias level p b erase level p e p w output waveform figure 14. typical waveform
ad9662 rev. c | page 9 of 16 table 4. i out control enable outenr outen2 outen3 i out 0 x x x off 1 1 1 1 off 1 0 1 1 (i inr gain r ) + i osr 1 1 0 1 (i in2 gain 2 ) + i os2 1 1 1 0 (i in3 gain 3 ) + i os3 table 5. oscillator control enable oscen outenr outen2 outen3 oscillator 0 x x x x off 1 0 x x x off 1 1 1 1 1 on 1 1 0 x x on 1 1 x 0 x on 1 1 x x 0 on
ad9662 rev. c | page 10 of 16 applications the ad9662 uses the current at one or more of its three inputsi inr , i in2 , and i in3 and generates an output current proportional to the input currents. channel r has a typical gain of 135 ma/ma, channel 2 has a typical gain of 130 ma/ma, and channel 3 has a typical gain of 260 ma/ma. the input impedance of channel r and channel 2 is typically 200 , and the input impedance of channel 3 is typically 100 . in most cases, a voltage output dac is used to set the dc current of these channels. a series resistor should be placed between each dacs output and its respective input channel. these resistors should be chosen to properly scale the input current while not excessively loading the output of the dac. channel r is used to provide bias current to the laser diode, and channel 2 and channel 3 are used to set the amplitudes of the current pulses that are required to write or erase the media. the output pulses are created by applying ttl level pulses to the channel enable pins while dc current is flowing into the input pins. channel 2 and channel 3 are turned on and off according to a predetermined write strategy (see figure 14 ). due to the fast rise and fall time (<1 ns) required for the operation of higher speed drives, trace lengths carrying high speed signals, such as enr, en2, en3, and the output current, should be kept as short as possible to minimize series inductance. a decoupling capacitor should be located near each v cc pin, and the ground return for the cathode of the laser diode should be kept as short as possible. rise time, t r , is defined as the time a pulse requires to transition from 10% of its final value to 90% of its final value. appropriately, fall time, t f , is defined as the time a pulse requires to go from 90% of its initial value to 10% of its initial value. propagation delay is defined as the time when a transitioning logic signal reaches 50% of its amplitude to when the output current, i out , reaches 50% of its amplitude. temperature considerations the ad9662 is in a 16-lead qsop. jedec methods were used to determine the ja of the qsop when mounted on a highly efficient thermally conductive test board (or 4-layer board). this board is made of fr4, is 1.60 mm thick, and consists of four copper layers. the two internal layers are solid copper (1 ounce/in 2 or 0.35 mm thick). the two surface layers (containing the component and back side traces) use 2 ounces/in 2 (0.70 mm thick) copper. this method of construction yields a ja for the ad9662 of approximately 105c/w. an integrated circuit dissipating 500 mw and packaged in a qsop, while operating in an ambient environment of 85c, has an internal junction temperature of approximately 138c. 85c + 0.500 w 105c/w = 138c this junction temperature is within the maximum recommended operating junction temperature of 150c. of course, this is not a realistic method for mounting a laser diode driver in an optical storage device. in an actual application, the laser diode driver would most likely be mounted to a flexible circuit board. the ja of a system is highly dependent on board layout and material. the user must consider these conditions carefully. some of the circuitry of the ad9662 can be used to monitor the internal junction temperature. the ad9662 uses diodes to protect it from electrostatic discharge (esd). every input pin has a diode between it and ground, with the anode connected to ground and the cathode connected to the particular input pin. the base-emitter junction of a pnp transistor is used for esd protection from each pin to v cc . the collector is electrically connected to the substrate of the die (see figure 15 ). the base- emitter junction of this transistor can be used to monitor the internal die temperature of the ic. using a 10 v source at the enable pin to forward-bias the base-emitter junction and a 1 m resistor to limit the current, a 2-point measurement can be used to calculate the junction temperature of the ic. because the enable pin (enable) needs to be a logic high for normal operation, the ad9662 can be operated with the 10 v applied through the 1 m resistor. the first point is obtained by measuring the voltage, v1, with i out = 0 immediately after the ad9662 is turned on. the case temperature, t1, can be measured using a thermocouple. the temperature of the case is measured immediately after the ic is turned on, and that temperature is the temperature of the transistor junction and of the die itself. through characterization of the ad9662, it was determined that the forward-bias voltage of the base-emitter junction of the transistor decreases by 1.9 mv for every 1c rise in junction temperature. the second point of the 2-point measurement is obtained when the ad9662 is operated under load. i out is adjusted until the increase in supply current is 200 ma. the ad9662 is allowed to reach thermal equilibrium, and then the voltage, v2, is measured. the voltage measurements taken with the ic running are lower than the actual base-emitter drop across the transistor due to the voltage drops across the internal resistance that is in series with the supply current (see figure 15 ). this finite resistance was calculated to be approximately 120 m. therefore, for a supply current change of 200 ma, the v be calculation is 24 mv too low. therefore, 24 mv must be added to the difference in measured voltages. the change in the base- emitter voltage is then calculated. v be = ( v2 + 24 mv C v1 )
ad9662 rev. c | page 11 of 16 using the preceding method, actual data was taken to determine the ja of the ad9662 in the evaluation board. immediately after power-up, v1 was measured to be 593 mv. the supply current was 27 ma. the ad9662 was adjusted to deliver 200 ma into a 10 load. this resulted in a total supply current of 244 ma. after allowing the part to reach thermal equilibrium, v2 measured 412 mv. the voltage drop across the 120 m internal resistor due to the change in supply current was then calculated. the change in junction temperature can then be determined. t j = t1 + v be /(1.9 mv/c) 5v ? + 10v enr v cc v1, v2 i be i cc ad9662 1m 04389-0-015 gnd r s (244 ma C 27 ma) 120 m = 26 mv this 26 mv internal voltage drop was then added to the measured voltage reduction to determine the actual v be. v be = (593 mv C 412 mv + 26 mv) = 207 mv the die temperature change measured 82.4c. the output of the ad9662 was at a voltage of 2 v. the part dissipated an additional 600 mw of power (3 v 200 ma). the ja for the ad9962 mounted on its 2-layer board was calculated to be: 600 mw/82.4c = 137c/w. figure 15. junction temperature measurement circuit this 2-point measurement allows the rise in die temperature to be calculated for any given power dissipation. the ja of the system can be calculated using the power dissipation of the ldd. v enr ? v cc (v) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 04389-0-014 40 20 60 80 100 120 140 160 temperature ( c) p d = v cc i cc C v diode i diode ja = ( t j C t1 )/ p d figure 16 shows a graph of the measured voltage between enr and v cc (v enr ? v cc ) vs. the die temperature. this graph was constructed using a 2-layer evaluation board for the ad9662 (see figure 17 ). figure 16. v enr ? v cc vs. internal temperature
ad9662 rev. c | page 12 of 16 evaluation board v s 5v enr v_out chip_en en2 oscen en3 ad9662 inr 1 in2 2 gnd 3 r f 4 v cc v cc i out gnd 16 15 14 13 in3 5 outenr 6 outen2 7 outen3 8 r s enable oscen v cc 12 11 10 9 dut1 r4 9.53k r9 23.7k c5 0.1 f r6 50 w3 dni r7 50 w2 dni r8 50 w1 dni r11 50 w4 dni r10 dni w5 r1 3.1 r12 46.4 vin2 vinw2 c2 0.1 f r3 4.32k vinr vinr c3 0.1 f r2 4.32k vin3 vinw3 c4 0.1 f r5 4.32k c1 0.1 f c8 dni r17 dni c9 0.1 f r13 5k c7 10 f v s v d gnd dni d1 04389-0-016 5v 5v 5v 5v 5v figure 17. ad9662 qsop-16 evaluation board schematic note: if dc logic levels are desired on the enable pins, then jump er w1 through jumper w5 should be used, and resistor r6 throu gh resistor r11 should not be installed. if the enable pins are driv en from external signal sources, then these resistors should b e installed, and the jumpers are not necessary.
ad9662 rev. c | page 13 of 16 outline dimensions compliant to jedec standards mo-137-ab 16 9 8 1 pin 1 seating plane 0.010 0.004 0.012 0.008 0.025 bsc 0.010 0.006 0.050 0.016 8 0 coplanarity 0.004 0.065 0.049 0.069 0.053 0.197 0.193 0.189 0.158 0.154 0.150 0.244 0.236 0.228 figure 18.16-lead shrink small outline package [qsop] (rq-16) dimensions shown in inches ordering guide model temperature range package description package option ad9662arqz 1 0c to 85c 16-lead qsop rq-16 ad9662arqz-reel 1 0c to 85c 16-lead qsop rq-16 ad9662arqz-reel7 1 0c to 85c 16-lead qsop rq-16 1 z = pb-free part.
ad9662 rev. c | page 14 of 16 notes
ad9662 rev. c | page 15 of 16 notes
ad9662 rev. c | page 16 of 16 notes ? 2005 analog devices, inc. all rights reserved. trademarks and registered trademarks are the property of their respective owners. c04389-0-11/05(c)

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