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| 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 features high linear velocity to follow the actuators used in conventional CD-R/RW drives. I I I I I I I I 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 function 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 maximum 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 following output current performance levels. * CD system total maximum drive current: 370 mA (figure 1) (VCC = 5 V, VOP = 2.5 V, T = 150 C) * DVD system total maximum drive current: 320 mA (figure 2) (VCC = 5 V, VOP = 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 x8-speed DVD recording. Support for a Variety of Timing Signals The CXA2680ER provides both differential inputs (LVDS/LVPECL) for higher speeds and single-ended inputs (3.3 V CMOS/TTL). Read Channel Low Noise Sony's 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). Small Package with Improved Heat Dissipation The CXA2680ER is provided in a 32-pin VQFN (4.8 x 4.8 mm) miniature package that can contribute to pickup miniaturization 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 connected 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 connected at the rear surface. 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 variations 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 V O I C E This function allows applications to set a modulator amplitude value that is optimal for the DVD media used. It's 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 accumulated know-how. 12 Output drive current temperature characteristics when input signals are applied to both write channels at the same time Vcc = 5 V, Vop = 2.5 V Output drive current temperature characteristics when input signals are applied to both write channels at the same time Vcc = 5 V, Vop = 3 V 500 450 400 350 300 250 200 150 100 50 0 25C 150C 0 100 200 300 400 Input current to each write channel [A] 450 400 350 300 250 200 150 100 50 0 Output current [mA] Output current [mA] 25C 150C 0 200 400 600 800 Input current to each write channel [A] I Figure 1 CD Output Drive Current Temperature Characteristics Write power 3 Write power 2 Write power 1 I Figure 2 DVD Output Drive Current Temperature Characteristics Read power Cool power 0 mW I Figure 3 Sample 5-Value Recording Waveform Mode control logic CMOS 3.3/TTL OSCMOD OUTEN2 OSCEN 100 xOUTEN2 LDEN1 LDEN2 GND2 8 LD1 (DVD) 7 6 5 4 3 GND1 2 1 9 LDOUT1 10k Iref Iref Iref Iref Iref Vref LDEN OSC CONT 32 OUTEN3 Timing control logic LVDS/LVPECL 100 10 RAMP2 10k 31 xOUTEN3 11 RAMP1 20k OSC 30 OUTEN4 100 12 RAMP11 29 xOUTEN4 13 Vcc_LD 1 22k 28 OUTEN5 100 14 R FREQ COMP 11k 27 xOUTEN5 1 15 R FREQ2 11k 26 OUTENREF 1 16 R FREQ1 25 VBG 17 LDOUT2 18 Vcc2 19 Vcc1 20 IIN5 21 IIN4 22 IIN3 23 IIN2 24 IIN1 LD2 (CD) 1 1 Voltage DAC I Figure 4 Application Circuit Example 13 |
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