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. 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 ■ 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 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’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). 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 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 E 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 differential 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 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. Output drive current temperature characteristics when input signals are applied to both write channels at the same time Output drive current temperature characteristics when input signals are applied to both write channels at the same time Vcc = 5 V, Vop = 3 V 25°C 150°C 0 200 100 300 450 400 350 300 250 200 150 100 50 0 Output current [mA] Output current [mA] Vcc = 5 V, Vop = 2.5 V 500 450 400 350 300 250 200 150 100 50 0 400 25°C 150°C 0 200 400 600 800 Input current to each write channel [µA] Input current to each write channel [µA] ■ Figure 1 CD Output Drive Current Temperature Characteristics ■ Figure 2 DVD Output Drive Current Temperature Characteristics Write power 3 Write power 2 Write power 1 Read power Cool power 0 mW ■ Figure 3 Sample 5-Value Recording Waveform 8 7 6 5 4 xOUTEN2 OUTEN2 GND1 OSCMOD 100 OSCEN LDEN2 GND2 LDEN1 Mode control logic CMOS 3.3/TTL 3 2 1 LD1 (DVD) Iref 10k Iref Iref Iref Iref 32 OUTEN3 100 Vref 31 10 xOUTEN3 RAMP2 10k 30 11 Timing control logic LVDS/LVPECL LDEN OSC CONT 9 LDOUT1 OUTEN4 RAMP1 OSC 100 20k 29 12 RAMP11 xOUTEN4 28 13 OUTEN5 Vcc_LD 100 1µ 22k 27 14 xOUTEN5 R FREQ COMP 1µ 11k 26 15 OUTENREF R FREQ2 1µ 11k 25 16 VBG R FREQ1 1µ 24 IIN1 23 IIN2 22 IIN3 21 IIN4 20 IIN5 19 Vcc1 LDOUT2 LD2 (CD) 18 Vcc2 17 1µ Voltage DAC ■ Figure 4 Application Circuit Example 13