12 voice it? been five years since i first started designing laser driver ics, and by now i have a good idea of what is required in laser driver ics. i strongly recommend that you look into the CXA2680ER, which was developed based on this ac- cumulated know-how. five-channel dual cd/dvd laser driver for ultra combo drives CXA2680ER sony developed the CXA2680ER as a dedicated laser driver ic that increases the number of channels to five to support increased bit depth recording strategies. the CXA2680ER also adds a dvd modulator amplitude switching function to the cxa2640er for use in dual drive systems and fea- tures high linear velocity to follow the actuators used in conventional cd-r/rw drives. cd system total maximum drive current: 370 ma dvd system total maximum drive current: 320 ma rise/fall time: 1 ns support for strategy in all 5 channels read channel low noise: 1.5 na/ hz high-frequency modulator frequency accuracy: < 10% built-in dvd modulator amplitude switching func- tion support for a variety of timing signals achieving both higher output and higher speed while both an increased output transient waveform speed and an increased maxi- mum output drive current are required to achieve increased linear velocities, increasing the maximum output drive current required increasing the size of the output transistors. however, increasing the size of the output transistors leads to delays in the output transient waveform. despite this tradeoff relationship, the CXA2680ER achieves both of the follow- ing output current performance levels. cd system total maximum drive current: 370 ma (figure 1) (v cc = 5 v, v op = 2.5 v, t = 150 c) dvd system total maximum drive current: 320 ma (figure 2) (v cc = 5 v, v op = 3 v, t = 150 c) thus this device can supply the required maximum output drive current even under severe operating conditions for both cd and dvd. furthermore, in the CXA2680ER, sony optimized the output transient waveforms to have both higher speed and a minimal amount of overshoot by including a built-in waveform shaping circuit. this allows this device to support 8-speed dvd recording. read channel low noise sony? painstaking low-noise design efforts to achieve the signal-to-noise ratio required for higher linear speeds achieved a noise level of 1.5 na / hz (at 20 mhz, 35 ma, 20 ma p-p). high-frequency modulator frequency accuracy in high-frequency modulator, which is used to reduce noise during playback, interference between the return light from the disc and the laser beam due to varia- tions in frequency causes noise to be aggravated. the CXA2680ER cancels frequency variations depending on the internal resistance caused by vco that has the emitter junction multivibrator, thus allowing noise to reduce. dvd system modulator amplitude switching function this function allows applications to set a modulator amplitude value that is optimal for the dvd media used. support for a variety of timing signals the CXA2680ER provides both differen- tial inputs (lvds/lvpecl) for higher speeds and single-ended inputs (3.3 v cmos/ttl). small package with improved heat dissipation the CXA2680ER is provided in a 32-pin vqfn (4.8 4.8 mm) miniature package that can contribute to pickup miniaturiza- tion through reductions in the mounting area. not only is the package size noteworthy, but this package can also increase the efficiency with which heat is dissipated, since it allows the heat sink to be con- nected with silicon grease to the die pads, which are exposed at the package surface. since this prevents heat from escaping through the pwb to the laser diode, pwbs using this device are easy on the laser diode. this also allows the ic to be con- nected at the rear surface.
13 25 c 150 c 400 300 200 500 450 400 350 300 250 200 150 100 50 0 vcc = 5 v, vop = 2.5 v 100 0 input current to each write channel [ a] output current [ma] output drive current temperature characteristics when input signals are applied to both write channels at the same time 25 c 150 c 800 600 400 450 400 350 300 250 200 150 100 50 0 input current to each write channel [ a] vcc = 5 v, vop = 3 v output current [ma] 200 0 output drive current temperature characteristics when input signals are applied to both write channels at the same time 8 9 10 11 12 13 14 15 16 32 31 30 29 28 27 26 25 7 6 5 4 3 2 1 17 18 19 20 21 22 23 24 10k 10k 20k ldout1 gnd2 lden1 lden2 oscen oscmod gnd1 xouten2 outen3 outen2 100 100 ramp2 ramp1 ramp11 vcc_ld 1 22k r freq comp 11k r freq2 11k r freq1 (dvd) ld1 timing control logic lvds/lvpecl xouten3 outen4 100 xouten4 outen5 100 xouten5 outenref 1 vbg 1 vcc2 ld2 (cd) vcc1 ldout2 1 1 iin5 iin4 iin3 iin2 iin1 voltage dac iref osc lden osc cont iref iref iref iref vref mode control logic cmos 3.3/ttl write power 3 write power 2 write power 1 read power cool power 0 mw figure 4 application circuit example figure 3 sample 5-value recording waveform figure 1 cd output drive current temperature characteristics figure 2 dvd output drive current temperature characteristics
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